EP1769065A1

EP1769065A1 - Vaccine composition against rhodococcus equi

Info

Publication number: EP1769065A1
Application number: EP05788683A
Authority: EP
Inventors: Saïd TAOUJI; Julien Cauchard; Jean-Jacques Ballet
Original assignee: Agence Francaise de Securite Sanitaire des Aliments (AFSSA)
Current assignee: Agence Nationale De Securite De L'alimentation De
Priority date: 2004-07-22
Filing date: 2005-07-12
Publication date: 2007-04-04
Also published as: WO2006021643A1; US8052978B2; FR2873386B1; FR2873386A1; US20080008726A1; CA2574516A1

Abstract

The invention concerns a method for preparing a soluble antigenic extract from Rhodococcus equi, comprising a step of solubilizing membranes of said bacteria by contacting said bacteria with an extraction solution containing a nonionic detergent of sorbitan polyethylene fatty acid ester type. The invention also concerns a soluble antigenic extract obtainable by said preparation method, said extract comprising membrane antigens of Rhodococcus equi dissolved in the extraction solution. Finally the invention concerns a composition comprising the soluble antigenic extract as medicine, comprising preferably a nanoparticulate or oil-in-water emulsion type adjuvant, and the use of the soluble antigenic extract for preparing a pharmaceutical composition for preventing or treating a Rhodococcus equi -induced infection in an animal.

Description

VACCINE COMPOSITION AGAINST RHODOCOCCUS EQUI

The invention relates to a method for preparing a soluble antigenic extract obtained from Rhodococcus egui, comprising a step of solubilizing the membranes of said bacteria by contacting these bacteria with an extraction solution containing a nonionic detergent of polyoxyethylene sorbitan fatty acid ester type. The subject of the invention is also a soluble antigenic extract obtainable from the preparation process, said extract comprising membrane antigens of Rhodococcus equi in solution in the extraction solution. The invention finally relates to a composition comprising the drug-soluble antigenic extract, preferably comprising a nanoparticulate adjuvant or oil-in-water emulsion, and the use of the soluble antigenic extract for the preparation of a pharmaceutical composition for preventing or treating Rhodococcus equi-induced rhodococcosis in a mammal.

Rhodococcus equi (or R. equi) causes pyo- granulomatous bronchopneumonia or other rarer clinical forms (digestive, osteo-articular) in foals. The morbidity rate varies from 5 to 17% in the different breeding regions of the world, and the case-fatality rate from 40 to 80%. In

In Normandy, Rhodococcus equi infections account for approximately 10% of mortality causes in foals aged 24 hours to 6 months, with annual variations related to climatic conditions (15% in 1988) and 70% of cases of bronchopneumonia in animals aged 1 to 6 months.

Currently, there are no effective means of medical prophylaxis. The bacterium is present in the soil of paddocks and pastures and the transmission is mainly by inhalation of contaminated dust from the environment. The disease develops insidiously and is clinically manifested only when the lung lesions are already very advanced so that the treatments Suitable antibiotics (Erythromycin-rifampicin combination) are often used too late to save foals. In addition, these antibiotic treatments are expensive.

The Rhodococcus equi bacterium is a real economic plague because of the mortality it causes, but also because of the consequences for the horse's career and the high cost of treatment. The insidious nature of the disease and the appearance of resistant strains make prevention through the development of an effective vaccine a priority in the fight against pathology.

Carrying is particularly important in the gut of horses, especially in the intestine of foals, where the insufficient development of the anaerobic flora encourages multiplication. Some authors even consider that

Rhodococcus equi is a normal host of the digestive tract of equines. The germ survives in the soil and can multiply in feces. This contamination of the external environment seems proportional to the density of the equidae and it is very important in farms maintaining horses for many years.

Rhodococcus equi infections have been reported in other animal species: in cattle and pigs, Rhodococcus equi is mainly isolated from normal lymph nodes or lymph nodes with lesions suggestive of tuberculosis. At the slaughterhouse, the existence of these adenitis leads to confusion with tuberculosis. In cattle, Rhodococcus equi is also responsible for pyometers and pneumonia. In piglets, the germ can cause the formation of abscesses in the oral cavity causing anorexia. In the goat, we note the formation of pulmonary, splenic or hepatic abscesses that can evoke Corynebacterium pseudotuberculosis infections. The formation of abscesses can be accompanied by the development of vertebral osteomyelitis. In sheep, some cases of pneumonia as well as abortions and neonatal mortalities have been described. In the cat, Rhodococcus equi causes adenitis of the lymphatic nodes of the anterior mediastinum and mesenteric lymph nodes, subcutaneous abscesses and the

wound infections. Cases of human infection with Rhodococcus equi have even been described. Most often, this bacterium is isolated in immunocompromised patients (infections with the HIV virus, immunosuppressive treatments, etc.).

The bacteria Rhodococcus equi belong to the genus Rhodococcus, in the class Actinobacteria, subclass of Actinobacteridae, order Actinomycetales, suborder Corynebacterineae, family Nocardiaceae. The term Coiynebacterium equi is sometimes also used to refer to Rhodococcus equi bacteria.

Rhodococcus equi is an optional Gram-positive intracellular bacterium that inhibits phagosome-lysosome fusion and is able to survive and multiply in phagocytic cells. The virulence factors are not fully known but they appear to be related to the capsule, equi factor synthesis, mycolic acids, 15-17 kDa molecular weight proteins and a 20 kDa protein.

More particularly, surface proteins of 15 to 17 kDa (or Vap proteins for "virulence-associated protein") are encoded by vap genes carried by plasmids of 85 to 90 kb. The analysis of the restriction fragments makes it possible to recognize at least 10 distinct plasmids whose distribution is linked to the geographical origin of the strains. In France, the virulent strains have an 85-kb type I plasmid or an 87-kb type I plasmid or an 85-kb type II plasmid that has only been found in French strains. These plasmids are only present in virulent strains and the strains of their plasmids survive less in phagocytes and are less pathogenic for the mouse or for the horse. The 7 identified vap genes (yapA, vapC, vapD, vapE, vapF, vapG and vapH), are located on a pathogenicity island and they code for surface proteins, essential for survival in macrophages, expressed at acid pH and at 37 ° C. but not at 30 ^° C. The sequence of the vapA gene appears very well preserved, so that a PCR test amplifying this gene makes it possible to diagnose virulent strains. In humans, strains isolated from the

Not all immunocompromised patients have such a plasmid, which contrasts with the isolated strains of diseased foals, all of which contain a plasmid carrying the vap genes. It is therefore likely that a state of immunodepression may allow the persistence of even slightly virulent strains.

Currently, no commercial vaccine to prevent the development of the disease is available in the world. Hyper-immune plasmas are marketed abroad (Great Britain, United States) but do not have marketing authorization in France. Moreover, their effectiveness is controversial. French breeders sometimes use autovaccines produced from local bacterial strains. This situation largely justifies the interest of the commercial development of a vaccine, which can for example be administered to pregnant mares.

Prescott et al. (Am J Vet Res, 1997 Apr; 58 (4): 356-9) used a VapA protein-rich fraction as the antigen. Vaccination elicits the production of immunoglobulin G (IgG) with opsonizing properties, so that the plasma of vaccinated animals can protect foals against experimental infection. However, vaccination of mothers followed by vaccination of foals does not provide any protection and could even increase the severity of infections.

The results obtained by Becύ et al. (Vet Microbiol 1997 Jun 16; 56 (3-4): 193-

204), using a culture supernatant containing the VapA proteins and "equi factor", show that the vaccination of the mares protects the foals by means of the colostral antibodies but that the vaccination of the foals is ineffective.

The use of inactivated strains leads to variable results according to the studies. However, for Varga et al. (Vet Microbiol, 1997 Jun 16, 56 (3-4): 205-12), vaccination of foals (2 or 3 injections between the ages of 3 and 7 weeks) provides protection. The amino acid sequence of the VapA protein was published in 1995 (Tan et al., Can J Vet Res., 1995 Jan; 59 (1): 51-9). Two epitopes of this protein, namely the Nl 5Y epitope corresponding to residues 65 to 78 of the mature VapA protein (Vanniasinkam et al., J Clin Microbiol, 2001 A rr 39 (4): 1633-7) and V 20 S corresponding to the residues 146 to 160 of the VapA protein (Taouji et al., FEMS

Immunol Med Microbiol. 2002 Dec 13; 34 (4): 299-306) have been designated as having potential as vaccines against R. equi. In addition, the article published on February 26, 2003 by the National Studs ("Immunization of pregnant mares against R. equi antigens: evaluation of the immune response and passive transfer in different Norman farms", Cauchard et al.) Describes a vaccine consisting of antigenic extracts of a virulent strain of R. equi (85Fp ⁺ ) combined with a nanoparticle-based adjuvant (MONTANIDE IMS3012 ^® ). However, this vaccine induces inflammatory reactions at the site of the injection.

It is therefore necessary to obtain both a qualitative and quantitative improvement of the passive protection conferred on the foal by colostrum. The inventors have thus been able to develop a new vaccine that induces a lasting immunity against R. equi, which is better tolerated by the subjects to whom the vaccine has been administered with fewer secondary inflammatory reactions, and which is simple to prepare.

This is precisely the object of the present invention.

Thus, according to a first aspect, the subject of the invention is a process for the preparation of a soluble antigenic extract obtained from Rhodococcus equi bacteria, characterized in that the said process comprises the following steps: a) the solubilization of the membranes of said bacteria by contacting these bacteria with an extraction solution containing a polyoxyethylene sorbitan fatty acid ester nonionic detergent, and b) recovering the solubilized antigenic extract in step a).

Information about Rhodococcus equi, namely systematics, bacteriological characteristics, habitat and pathogenicity, power pathogenicity, bacteriological and serological diagnosis, antibiotic susceptibility, and prophylaxis are widely described in the veterinary bacteriology dictionary available on the World Wide Web. address http://www.bacterio.cict.fi:/bacdico/garde.html.

The R. equi bacteria used in the process according to the invention are obtained by culturing in a medium and under conditions suitable for carrying out the invention; preferably, said bacteria are suspended in the culture medium ("wet bacteria"). Without limitation, an example of a suitable culture medium is the brain-heart medium (BHI for "Brain Heart").

Infusion ") at a pH of between 5 and 7, preferably between 6 and 7, and particularly preferably of 6.5. The appropriate culture conditions are generally room temperature, preferably 37 ° C, with stirring, for example 150 rpm (revolutions per minute), for one to several days, preferably for 48 to 72 hours, so that said bacteria are in the exponential phase of growth.

In the appropriate culture medium, said bacteria may be from the same strain or different strains, the bacteria of different strains being, in the latter case, mixed in the medium. All R. equi strains can be used for carrying out the present invention. As an example of R. equi strains, mention may be made of, but not limited to, strains ATCC33701, ATCC6939, ATCC2572, and strain 85F deposited at the CNCM (National Collection of Culture of Microorganisms, Institut Pasteur, France). July 2, 2004 under the number 1-3250. All R. equi strains possessing a virulence plasmid can be used in the context of the present invention. Nevertheless, any R. equi strain, cured of its plasmid or naturally deprived, to which an expression vector containing one or more genes of the pathogenicity island of the natural plasmid is added, can also be used in the of the present invention.

In order to recover a soluble antigenic extract from R. equi, the membranes of these bacteria are solubilized by contacting said bacteria, which can to be suspended in an extraction solution containing a polyoxyethylene sorbitan fatty acid ester, which is a nonionic detergent (however, it should be noted that the antigenic extract of R. equi obtained is likely to contain R. equi antigens other than membrane antigens). This type of non-ionic detergent is in particular described in the book "Handbook of pharmaceutical excipients", ^2nd edition, "A seal publication of the American Pharmaceutical Association and the Royal Pharmaceutical Society of Great Britain," The Pharmaceutical Press, Published by A WADE and PJ. WELLER, 1994. Examples of polyoxyethylene sorbitan fatty acid esters which can be used in step a) of solubilization of R. equi bacteria membranes of the process according to the invention include, but are not limited to limited to, the following compounds, commercially available: monolaurate polyoxyethylene 20 sorbitan, also called polysorbate 20 or Tween 20 ^® (AMRESCO, Solon, OH), polyoxyethylene monolaurate (4) sorbitan, also known as polysorbate 21, or Tween ^21® , the polyoxyethylene sorbitan monopalmitate, also called polysorbate 40, or Tween ^40® ,

- monostearate polyoxyethylene 20 sorbitan, also called polysorbate 60 or Tween 60 ^®, polyoxyethylene monostearate (4) sorbitan, also called polysorbate 61 or Tween 61 ^®, sorbitan tristearate, polyoxyethylene 20 sorbitan, also known as polysorbate 65, or Tween 65 ^®, - sorbitan monooleate polyoxyethylene 20 sorbitan, also called polysorbate 80 or Tween 80 ^®, polyoxyethylene monooleate (5) sorbitan, also called polysorbate 81 or Tween ^® 81,

- trioleate polyoxyethylene 20 sorbitan, also called polysorbate 85 or Tween ^® 85, and monoisostearate polyoxyethylene 20 sorbitan also called polysorbate 120. The suppliers of these polyoxyethylene sorbitan fatty acid esters are known to those skilled in the art (SIGMA, AMRESCO, etc.) •

In a particular embodiment, the polyoxyethylene sorbitan fatty acid ester is selected from polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, and polyoxyethylene sorbitan monooleate.

According to a particularly preferred embodiment, the polyoxyethylene sorbitan fatty acid ester is polyoxyethylene sorbitan monolaurate.

Preferably, the preparation method according to the present invention is characterized in that said nonionic detergent is at a concentration of between 0.01% and 5% in said extraction solution.

Particularly preferably, the concentration of the nonionic detergent is 0.1% in said extraction solution.

Preferably, in step a) of solubilization of the preparation method according to the present invention, the contacting of the bacteria with the extraction buffer is carried out at a proportion of 1 ml to 20 ml of said buffer per gram of wet bacteria. . Most preferably, this proportion is 5 ml of said buffer per gram of wet bacteria.

By wet bacteria is meant bacteria suspended in a liquid medium.

According to another particular embodiment, the preparation process according to the present invention is characterized in that the Rhodococcus equi bacteria are of the strain selected from strains ATCC33701, ATCC6939, ATCC2572, and strain 85F deposited at the CNCM on July 2, 2004. under the number 1-3250. In a particularly preferred manner, the Rhodococcus equi bacteria are of 85F strain deposited at the CNCM July 2, 2004 under the number 1-3250. According to yet another embodiment, the preparation method according to the present invention is characterized in that said bacteria are in the form of a bacterial pellet obtained after centrifugation, before step a). This centrifugation step has the advantage of removing the impurities so as to recover only the bacterial cells. Methods other than centrifugation, well known to those skilled in the art, may also be used for this purpose. Bacteria in the form of a bacterial pellet are obtained by centrifugation under appropriate conditions known to those skilled in the art. Preferably, the centrifugation making it possible to obtain the bacterial pellet before step a) is carried out at a speed of between 1000 g and 50000 g, preferably 10,000 g, for a period of 1 min to 45 min, preferably 20 min. preferably at a temperature of between 10 ^° C. and 6 ° C., preferably 4 ° C.

Preferably, the bacterial pellet is washed at least once in a suitable washing buffer before step a).

Those skilled in the art are aware of the washing buffers suitable for washing the bacterial pellet. Preferably, Tris acetate buffers are used at a suitable concentration and pH, for example at a concentration of 10 mM or

25 mM, for example at a pH of between 7 and 8, preferably at a pH of 7.5. Preferably, said wash buffers are filtered (for example using a 0.2 μm filter, ....).

More preferably, two successive washes of the bacterial pellet obtained after centrifugation in a 10 mM Tris acetate buffer pH 7 to 8, followed by a third washing in a 25 mM Tris acetate pH 7.5 buffer. Preferably, step a) of solubilization is carried out with stirring, at a temperature in the range of 20 to 40 ° C, particularly preferably 37 ⁰ C, for a period of 30 to 150 min, particularly preferably preferred for 90 minutes, preferably in the presence of microbeads.

Step b) of recovery of the antigenic extract solubilized in step a) can be carried out according to various appropriate techniques, such as in particular centrifugation, filtration, chromatography. According to a particular embodiment, the preparation process according to the present invention is characterized in that in step b) the product is centrifuged. obtained in step a), and the centrifugation supernatant containing said solubilized antigenic extract is recovered.

The centrifugation in step b) of the product obtained in step a) is carried out under appropriate conditions, known to those skilled in the art. Preferably, this centrifugation is carried out at a speed of between 10,000 g and 150,000 g, preferably 100,000 g, for a period of 10 minutes to 120 minutes, preferably for 60 minutes, at a temperature of between 1 and 60 ^° C. preferably at ^{40 °} C. Even more preferably, the centrifugation supernatant containing said solubilized antigenic extract is stored at a temperature of between 1 and 60 ^° C., preferably at 4 ° C.

In a particularly preferred manner, the preparation process according to the invention is characterized in that the Rhodococcus equi bacteria are of strain 85F deposited at the CNCM on July 2, 2004 under the number 1-3250, and in that the ester of The polyoxyethylene sorbitan fatty acid is polyoxyethylene sorbitan monolaurate.

According to a second aspect, the subject of the present invention is a process for preparing a soluble antigenic extract obtained from bacteria

Rhodococcus equi strain 85F deposited at the CNCM July 2, 2004 under the number 1-3250, characterized in that said method comprises the following steps:

Obtaining a bacterial pellet by centrifugation of said bacteria

Rhodococcus equi suspended at a rate of 10000 g for 20 minutes, preferably at a temperature of 4 ° C.

- Two successive washes of the bacterial pellet obtained in a 10 mM Tris acetate buffer of pH 7 to 8, followed by a third wash in a Tris acetate buffer

25 mM pH 7.5,

Solubilization of the bacterial membranes of the washed bacterial pellet by contacting said pellet with an extraction solution containing polyoxyethylene sorbitan monolaurate at a concentration of 0.1% v / v in said extraction solution, the proportion of bacteria; extraction buffer being 5 ml / g of wet bacteria, said solubilization being carried out under stirring for 90 minutes at a temperature between 35 and 40 ⁰ C, preferably in the presence of microbeads, and

The product obtained in the preceding step is centrifuged at 100000 g for 1 hour, preferably at 4 ° C., and the centrifugation supernatant containing said solubilized antigenic extract is recovered.

The R. equi bacteria used in the process according to the invention are obtained by culturing in a medium and under conditions suitable for carrying out the invention; preferably, said bacteria are suspended in the culture medium. Without being limited thereto, an example of a suitable culture medium is the Brain Heart Infusion (BHI) medium at a pH between 5 and 7, preferably between 6 and 7, and particularly preferably of 6.5. The appropriate culture conditions are generally room temperature, preferably 37 ° C, with stirring, for example 150 rpm, for one to several days, preferably for 12 to 72 hours, so that said bacteria are in the exponential phase growth.

During the solubilization step, the microbeads can be used to "break" the bacteria. It is possible to use, for example, glass beads with a diameter of 150 to 212 μm (SIGMA, Lyon, France).

According to a third aspect, the subject of the invention is a soluble antigenic extract of Rhodococcus equi bacteria, obtainable from the process according to the present invention, characterized in that the said extract comprises R. equi membrane antigens in solution. in an extraction solution containing a polyoxyethylene sorbitan fatty acid ester nonionic detergent.

According to a particular embodiment, the soluble antigenic extract of Rhodococcus equi bacteria according to the invention is obtained from the preparation method according to the present invention. According to another particular embodiment, the soluble antigenic extract of Rhodococcus equi bacteria according to the invention is characterized in that it comprises R. equi membrane antigens in solution in a solution containing a nonionic detergent of polyoxyethylene sorbitan fatty acid ester type.

The R. equi membrane antigens included in the soluble antigenic extract according to the invention may be derived from the same strain R. equi or different R. equi strains, the R. equi bacteria of different strains being, in the latter case, mixed in the middle. All R. equi strains can be used for carrying out the present invention. Examples of R. equi strains include, but are not limited to, strains

ATCC33701, ATCC6939, ATCC2572, and strain 85F deposited at the CNCM July 2, 2004 under the number 1-3250, the latter being particularly preferred.

As already mentioned above, all R. equi strains possessing a virulence plasmid can be used in the context of the present invention.

Nevertheless, any R. equi strain, cured of its plasmid or naturally deprived, to which an expression vector containing one or more genes of the pathogenicity island of the natural plasmid is added, can also be used in the of the present invention.

Preferably, the soluble antigenic extract of Rhodococcus equi bacteria according to the invention is characterized in that the polyoxyethylene sorbitan fatty acid ester is chosen from polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate and monostearate. polyoxyethylene sorbitan, and the polyoxyethylene sorbitan monooleate.

Particularly preferably, the soluble antigenic extract of Rhodococcus equi bacteria according to the invention is characterized in that the polyoxyethylene sorbitan fatty acid ester is polyoxyethylene sorbitan monolaurate.

Preferably, the soluble antigenic extract of Rhodococcus equi bacteria according to the invention is characterized in that said nonionic detergent is at a concentration of between 0.01% and 5% in said extraction solution. In a particularly preferred manner, the soluble antigenic extract of bacteria

Rhodococcus equi according to the invention is characterized in that the concentration of the nonionic detergent is 0.1% in said extraction solution. Most preferably, the soluble antigenic extract according to the invention is characterized in that the Rhodococcus equi bacteria are of strain 85F deposited at the CNCM on July 2, 2004 under the number 1-3250, and in that the ester The polyoxyethylene sorbitan fatty acid is polyoxyethylene sorbitan monolaurate.

According to a fourth aspect, the subject of the invention is a composition comprising the soluble antigenic extract according to the present invention, as a medicament. Preferably, the composition according to the invention as a medicament additionally comprises adjuvants of the immunity; these adjuvants may be of any type known to those skilled in the art, insofar as, when they are mixed with an effective amount of the soluble antigenic extract according to the present invention, they make it possible to increase the antigenicity of the composition and to promote a superior immune response. Preferably, the composition according to the invention is characterized in that it additionally contains an immunity adjunct of the nanoparticulate type or of the oil-in-water emulsion type.

Examples of adjuvants for oil-in-water emulsion immunity include vaccine adjuvants providing an oil-in-water emulsion and containing a non-mineral oil. Such adjuvants, very well tolerated, are adapted to induce short-term immunity, with a humoral meditation response. Preferably, the adjuvant an oil-in-water emulsion containing a non-mineral oil adjuvant Montanide ISA 35 ^® (SEPPIC, Paris, France). Generally, the adjuvant Montanide ISA 35 ^® contains glycerol ester, squalane and Panhydromannitol octodecenoate ether, preferably in the following proportions: Glycerol ester: 50%, squalane: 10% ether and anhydromannitol octodecenoate: 40 %.

Mention may also be made of, but not limited to, the following adjuvants of the oil-in-water emulsion type: the adjuvant composition described in the international patent application published November 11, 1999 under the number WO 99/56776 (RIBI ImmunoChem Research Inc.), which is a stable oil-in-water emulsion comprising a metabolizable oil, one or more surfactants, an antioxidant and a compound for rendering the isotonic emulsion; the submicron oil-in-water emulsions described in the international patent application published on June 24, 1999 under the number WO 99/30737 (CHIRON Corp.), relating to vaccine compositions comprising, on the one hand, biodegradable microparticles with antigens included or adsorbed, on the other hand, such submicron oil-in-water emulsions;

the adjuvant composition for vaccines comprising a metabolizable oil and an emulsifying agent, in which the oil and the emulsifying agent are present in the form of an oil-in-water emulsion (oil droplets with a diameter of approximately 1 micron), as described in the international patent application published December 13, 1990 under the number WO 90/14837 (CHIRON Corp.); and

the adjuvant for polysaccharide vaccines comprising an oil-in-water emulsion system containing a light non-biodegradable hydrocarbon oil or a biodegradable oil and a detergent, as well as a detoxified endotoxin, as described in the US patent published on February 7, 1989 under US 4,803,070 (RIBI ImmunoChem Research Inc.).

Examples of adjuvants of the immunity of nanoparticulate type include adjuvants for vaccines based on liquid nanoparticles associated with an immunostimulant having GRAS status. Such adjuvants, well tolerated, are based on a new concept combining the adjuvant properties of nanoparticles and a new immunostimulant. Preferably, the adjuvant of liquid nanoparticles associated with an immunostimulating having the GRAS status is the adjuvant MONTANIDE ^® IMS 301x (SEPPIC, Paris, France ^1), particularly preferably the IMS 3012 MONTANIDE ^®. In general, this adjuvant

MONTANIDE IMS 3012 ^® contains modified corn oil, saline buffer solution and preservative, preferably in the following proportions: modified corn oil: 10%, saline buffer solution: 89.99% and preservative: 0 , 01%.

Mention may also be made of, but not limited to, the following nanoparticulate adjuvants: the small particles (average diameter: 200 nm) used in particular for the administration of biologically active agents, described in the international patent application published October 23, 2003 under the number WO 03/087021 (GENESEGUES company). Such particles comprise a biologically active agent such as in particular an adjuvant, a surfactant, and a soluble polymer in aqueous solution;

the solid adjuvant composition of vaccine in the form of a powder or granules comprising an injectable solid support on which a liquid is capable of being absorbed, adsorbed, impregnated or anchored, described in the international patent application published on December 5, 2002 under the number WO 02/096386

(SEPPIC company); the adjuvants for solid lipid nanoparticle type vaccines described in international patent applications WO 00/71077 (published November 30, 2000 - PHARMASOL company), WO 00/71154 - (published November 30, 2000 - PHARMASOL company), and in the Mϋller et al. (Eur J

Pharm Biopharm 2000 JuI; 50 (1): 161-77 - cf. paragraph 12, page 13); solid phase admixtures of the metal salt type, in particular aluminum hydroxide gel (ALHYDROGEL), described in the international patent application published on May 11, 2000 under the number WO 00/25812 (LEES Andrew). Such adjuvants are described as being used in a method for preparing conjugate vaccines;

the liquid formulation comprising a discontinuous phase of microparticles in a nonaqueous liquid continuous phase, described in the international patent application published on 24 September 1998 under the number WO 98/41188 (EASTBRIDGE Limited). The microparticles described contain pulverized sugars carrying at least one biomolecular product such as a drug or other biologically active ingredients such as a protein, an antibody or an enzyme. Such a formulation can be used as a vaccine; surface-modified diamond nanoparticles as antigen delivery vehicles (adjuvants) described in Kossovsky et al., Bioconjug Chem 1995 Sep-Oct; 6 (5): 507-11; and the microspherical particles consisting of a continuous matrix of a biodegradable polymer, which matrix contains in particular an immunogen adsorbed on an aluminum salt adjuvant (aluminum hydroxide, aluminum phosphate, etc.), described in the application International patent published on July 21, 1994 under the number WO 94/15636 (CSL company

Limited).

According to one particular embodiment, the composition according to the invention is obtained by mixing the soluble antigenic extract according to the invention with the adjuvant of the immunity, preferably the adjuvant of the nanoparticle type immunity, under gentle stirring for a period of 1 minute to 5 hours, preferably 10 minutes, at a temperature between 1 and 6 ° C, preferably 4 ° C.

Preferably, before mixing the soluble antigenic extract with the immunity adjuvant, said soluble antigenic extract is previously diluted to a concentration of between 0.5 and 10 mg / ml in the extraction buffer or any other buffer known to those skilled in the art to retain the structural properties and solubility of proteins. There are many buffers of different compositions for diluting the proteins that can be used in this case. More preferably, the soluble antigenic extract is diluted to a concentration of 1 mg / ml. Optionally, the dilution of the soluble antigenic extract is followed by a filtration step or any other method to maintain sterile conditions.

Particularly preferably, the composition according to the invention is characterized in that the immunity adjuvant of nanoparticulate type is the adjuvant MONTANIDE IMS 3012 ^®. Most preferably all, the composition of the invention contains 50% of the soluble antigenic extract and 50% of the nanoparticulate adjuvant MONTANIDE IMS 3012 ^®.

According to another embodiment of the invention, the composition of the present invention is characterized in that the immunity adjuvant of oil-in-water emulsion adjuvant is Montanide ISA 35 ^®. Preferably, the composition of the invention contains 75% soluble and 25% antigenic extract of the oil-in-water emulsion adjuvant Montanide ISA 35 ^®.

According to a fifth aspect, the invention relates to the use of a soluble antigenic extract according to the present invention, for the preparation of a pharmaceutical composition for preventing or treating an infection with R. equi in a mammal. Preferably, the mammal is an equine. R. equi infections in mammals are the cause of various diseases, including diseases of the respiratory system. Examples of R. equi-induced diseases include, but are not limited to, foal, pyo-granulomatous bronchopneumonia, multifocal ulcerative enterocolitis and typhlitis often associated with suppurative adenitis of the mesenteric and colonic lymph nodes, septic arthritis, osteomyelitis, and more rarely, lymphangitis, suppurated myositis and cellulitis, and subcutaneous abscesses.

In adult horses, the disease is sporadic and results in pulmonary or colonic adenopathies, infected wounds; the bacterium was also isolated on equine fetuses during abortions. Rhodococcus equi infections have been described in other mammalian species (cattle, pigs, sheep, goats, llamas, dogs, cats ...) for which, in general, the clinical expression of the disease remains rare. In most cases, the lesions observed are adenopathies, suppurated or not; pneumonia is exceptional but has been reported, among others, in sheep, goats and llamas.

On the other hand, in humans, as in foals, pneumonia is the predominant clinical manifestation of Rhodococcus equi infections. Thus, preferably, the use according to the present invention is characterized in that infection with R. equi induces a disease of the respiratory system, including pneumonia. More preferably, the use according to the present invention is characterized in that the pharmaceutical composition further comprises an adjuvant of the immunity.

More preferably, the immunity adjuvant is of the nanoparticulate type or of the oil-in-water emulsion type.

Particularly preferably, the use according to the present invention is characterized in that the pharmaceutical composition further comprises an adjuvant of immunity nanoparticulate type which is the adjuvant MONTANIDE IMS 3012 ^®. Most preferably all, the use according to the present invention is characterized in that the pharmaceutical composition contains 50% of the soluble antigenic extract and 50% of the nanoparticulate adjuvant MONTANIDE IMS 3012 ^®.

According to another embodiment, the use according to the present invention is characterized in that the pharmaceutical composition further comprises an adjuvant of immunity of oil-in-water emulsion which is the adjuvant Montanide ISA 35 ^®.

Preferably, the pharmaceutical composition contains 75% of soluble antigenic extract and 25% of adjuvant oil-in-water emulsion MONTANIDE ^® ISA 35.

The pharmaceutical composition for preventing or treating R. equi infection may be administered in any suitable manner in a mammal, preferably an equine.

Preferably, the use according to the present invention is characterized in that the pharmaceutical composition is administered to said mammal intramuscularly or subcutaneously.

According to a particular embodiment, the use according to the present invention is characterized in that the mammal is selected from man and non-human mammals, such as cattle, pigs, sheep, goat, cat. Preferably, the mammal is an equine, such as in particular the horse. Preferably, said pharmaceutical composition is administered to the foal after birth, preferably in 1 to 4 doses depending on the degree of contamination of the environment.

Particularly preferably, the use according to the invention is characterized in that the pharmaceutical composition is intended for the prevention or pre-natal treatment of a pregnant foal, said pharmaceutical composition being administered to the pregnant horse. Preferably, said pharmaceutical composition is administered in 1 to 4 doses depending on the degree of contamination of the environment.

The legends of the figures and examples which follow are intended to illustrate the invention without in any way limiting its scope.

LEGEND OF FIGURES

Figure 1: Anti-i? IgG levels. equi in mares immunized with antigens containing VapA protein (Group 1), mares immunized with killed R. equi whole bacteria (Group 2) and control mares. IgG levels were determined by ELISA. The results are expressed in arbitrary units (AU) + 1 standard error. Statistical significance of the differences between Groups 1 (A), 2 (•) and control (B): * p <0.05, ** p <0.01, *** p0.001.

Figure 2: Western-blot detection of anti-VapA serum antibodies. The technique illustrates the binding of the antibodies contained in the sera tested to the 15 KDa band corresponding to VapA.

VapA = rabbit anti-VapA polyclonal antibody (arrow)

A = mare - foal pair (control group)

B = mare - foal pair (group 1) C = mare - foal pair, significant antibody transfer (group 2)

D = mare - foal pair, no antibody transfer (group 2)

1 = sera of mares before immunization 2 = sera of mares 45 days after immunization

3 = foals of the foals 30 days after birth

FIG. 3: Kinetics of arG-R.equi IgGs in foals from mares immunized with antigens containing the VapA protein (Group 1, "Gl"), mares immunized with killed R. equi whole bacteria (Group 2,

"G2") and control mares (control group "GT", healthy foals "G _sa i _nS ", foals with rhodococcosis "G _rhodoc ") • The results are expressed in arbitrary units (AU) + 1 standard error according to the number of days after birth. Statistical significance of differences: * p <5%, ** p <1%, *** p <1% o.

Figure 4: Opsonisation of R. equi by neutrophils of mares and foals, controls ([]) group 2 (() and group 1 (|) The results are expressed in number of adherent bacteria per 200 neutrophils.

The sera were tested before the first immunization (Day 0) and after the second immunization (day 45) for the mares, 30 days after birth for the foals. Statistical significance of the differences: * p <5%, ** p <1%, *** ρ <1%.

EXAMPLES

EXAMPLE 1 PROTOCOL FOR PREPARING VACCINE ANTI-R. EQUI FOR GRAVID MARS (EXTRACTION OF ANTIGENS TO TRITON)

The objective of this example is to evaluate the effect of immunization of a pregnant mare with a potential vaccine containing VapA associated with a nanoparticulate adjuvant, on specific IgG levels and serum opsonizing activity, transmitted to the foal via colostrum, and the occurrence of R. equi pneumonia. 1. Materials and methods

1.1 Preparation of Rhodococcus equi antigens

The purified solution of R. equi proteins containing Vap A was prepared from strain 85F and characterized by western-blot. An injection was composed of 1 mg of protein diluted in 0.5 ml of tris acetate buffer, pH 8.5, 2% Triton X-100 (Sigma, St Quentin Fallavier, France), combined with 0.5 ml of adjuvant aqueous nanoparticles (IMS 3012, SEPPIC Laboratories, Castres, France). The control animals received the same solution without the proteins. Group 2 mares were immunized with a saline solution containing 1.10 ⁹ fixed bacteria, derived from a culture from a foal colt that died of rhodococcosis in one of the stud farms.

1.2 Animals

Forty-eight pregnant mares (26 French-Trotter, 16 Thoroughbred and 6 ponies, 11-year-old with an interval of 5 to 17 years) whose term dates were from January to July 2002 were been included in the study. They were stationed in 3 stud farms that were enzootically infected by the disease and located in 2 lower Normandy departments (Calvados and Orne). Each mare remained in the same farm at least 6 months before the end of the term and 6 months after foaling.

Seventeen of the 48 broodmares had been immunized 3 times during the previous gestation with whole R. equi bacteria killed and the other horses had never been immunized against R. equi. The mares to be immunized in the study were divided into 2 groups: group 1 (24 mares) consisted of mares receiving antigens containing the VapA protein and group 2 (8 mares) of mares receiving the bacterium total killed (autovaccine). Immunization was performed by intramuscular injection into the neck.

The animals that received the autovaccine during the previous gestation were distributed 9/24 in group 1 and 8/8 in group 2. The animals in the control group (15 mares) were paired with those in group 1 according to the term dates. The numbers of foals included in the study were respectively 23, 7 and 13 in groups 1, 2 and control, because of a case of stillbirth related to dystocia in group 1 and an interruption of follow-up in the other 3 cases.

1.3 Immunization protocol

Injections were given at 9, 6 and 3 weeks before the presumed term in groups 1 and 6 and 3, and 1 month before the assumed term in group 2.

After immunization, the sera were collected weekly until the end, except in 22 broodmares for which the last blood test could not be carried out because of premature foaling. The foals were taken at birth, after colostrum (ie 24 hours of life) and at 30 and 45 days of age. Colostrum was collected at birth. These samples were stored at -2O ⁰ C until analysis.

1.4 Detection of anti-Rhodococcus equi IgG

IgGs were assayed by ELISA method. 96-well plates (Nalge Nunc,

Rochester, NY, USA) were coated (1 μg / well) with the protein solution containing VapA (Cf 1.1) diluted in PBS overnight at 4 ° C, then washed three times with PBS, 0.05% v / v. Tween 20, (PBST), and saturated with PBS buffer, 1% BSA overnight at ^{40 °} C., then washed three times. The sera were added in triplicate at three dilutions (1/100, 1/1000, 1/50000) and incubated at 37 ° C for one hour.

After three PBST washes, the secondary peroxidase-coupled goat anti-horse IgG antibody (1/1600, Bethyl Laboratories, Montgomery, TX, USA) was incubated for one hour at 37 ° C. After three washes, 100 μl of TMB (3,3 ', 5,5'-tetramethylbenzidine) ready for use (Uptima, Interchim, Montlucon, France) were deposited and incubated for 20 min at room temperature. The reaction was stopped by the addition of H ₃ Pθ ₄ IM. The optical density was read at 415 nm on an automatic spectrometer. The retained OD value was determined by subtracting the average OD of the control wells from the OD of the experimental sera. The results are expressed in arbitrary units (mean OD for 1/1000 dilution, and 1/10000 and 1/50000 OD extrapolated to 1/1000). The limit of detection was experimentally determined by Western blot with a serum free of antibodies against Rhodococcus equi.

1.5 Western blot

The VapA-containing protein solution migrated on a 12% SDS-PAGE gel. The proteins were transferred to a nitrocellulose membrane for 90 min at 90 volts. The membranes were blocked overnight at ^{40 °} C. in a solution of TBS-T containing 5% BSA and then washed three times with TBS-T ("Tris buffer saline" or salt buffer, known to man art, associated with Tween). The presence of 15 Kda VapA bands was monitored with a polyclonal anti-VapA rabbit antibody (1/2000) prepared by immunization with VapA peptides and revealed (1/30000) by secondary goat anti-IgG antibodies. rabbit coupled with alkaline phosphatase (Sigma, St Quentin Fallavier, France). Horse IgG attached to R. equi antigens after incubation for 1 hour at 37 ° C and three washes were revealed by a secondary antibody (1/5000) of goat anti-lamb IgG coupled to alkaline phosphatase (Bethyl, Montlucon, France). After three washes with the TBS-T solution, the revelation was marked by the addition of 5-bromo-4-chloro-3-indolyl phosphate / p-nitro blue tetrazolium (Uptima, Interchim, Montlucon, France). The reaction was stopped by the addition of water.

1.6. Evaluation of the opsonizing capacities of the sera

It was a question of counting the number of R. equi phagocytés by the neutrophils of a clinically healthy adult horse. Freshly collected blood samples from which the erythrocytes were lysed (Hybrimax, Sigma) were centrifuged (200g, 10 min, room temperature). The cell pellet was suspended in a Hanks solution. The cells were incubated for 20 min with bacteria from an 85F exponential culture in the presence of the undecomplemented sera to be tested, then fixed for 5 min in a 0.5% glutaraldehyde solution and stained with Giemsa. The number of bacteria fixed on 200 polymorphonuclear neutrophils was counted independently by two people (immersion microscope, 1000 X). The controls were devoid of horse serum.

1.7 Clinical follow-up

In mares, local inflammatory reactions at the injection site have been noted. Cases of R. equi infection in foals during the first 6 months of life were also recorded following confirmation by bacterial isolation from tracheal lavage fluid, blood and feces.

1.8 Statistical analyzes Whenever appropriate, the results were expressed as an average ± a standard error.

The influence of mares immunization on colostral IgG levels, the proportion of mares with anti-VapA antibodies in the different groups and the comparison of the prevalence of the disease in the foals of the 3 groups were analyzed by ANOVA, χ ² test and Fisher's exact test, respectively (Statview 5.0 software).

The effects of mares immunization on the kinetics of specific IgG in foals were studied using a linear model (GLM procedure, SAS 8.2 software).

2. Results

2.1 Serum IgG levels against R. equi in pregnant mares before and after immunization IgG levels determined by ELISA before immunization were significantly higher in group 2 than in the other 2 groups

(Figure 1).

In 3 mares of group 1, significant inflammation was observed at the injection site and disappeared in 24-48 hours. After injection of the antigenic preparation containing VapA, the specific IgG levels increased between OJ and J7 and then reached a plateau which remained until J56. From the ^7th day, the levels of group 1 antibodies were significantly higher than in the other 2 groups.

The presence of anti-VapA IgG was detected by immunoblots as shown in Figure 2. As expected, the ratio of animals with specific antibodies prior to immunization was higher in group 2 than in group 1 because of history of immunization (Table 1). All but one control group lacked detectable anti-VapA antibodies. Immunization with VapA-containing antigens resulted in the presence of anti-R equi IgG in 23 out of 24 women in group 1, regardless of their pre-immunization status, a higher ratio than in group 2 (p <0, 01). Most foals in group 1 showed serum-specific antibodies at 30 days postnatal, and this at a higher frequency than in group 2 (p <0.0001) which differed only slightly from that of foals in the control group ( p = 0.04).

Table 1: Number of animals with antibodies to Vap A detected by western-blot in mares before / after immunization and foals.

Mares Mares Foals

OJ J45 * J30 **

Group 1 8/24 23/24 22/23

Group 2 6/8 7/8 4/7

Witnesses 1/15 2/15 4/13

The results are expressed as a ratio of the number of animals possessing anti-i? equi detected by western-blot on the number of animals in the corresponding group. * After immunization ** After birth 2.2 Measurement of colostral antibodies

IgG dosed with ELISA were significantly more abundant in colostrum of mares in group 1 (mean 2.124 AU ± 0.035) and group 2 (mean 1.928 ± 0.160) than in control mares (mean 1 ± 0.147)

(p <0.0001 and p = 0.0005, respectively) although no significant difference was observed between the 2 immunized lots (p> 0.05).

2.3 Kinetics of serum IgG anti-R equi post-immunization in foals

The results are detailed in Figure 3. At birth, serum IgG anti-R. equi detectable by ELISA were not found in any foals (newborns). After colostrals, the 24-hour foals showed anti-i? Antibody levels. equi of those of their mother (p> 0.05, data not shown). Group 1 foals had higher antibody levels than in group 2 (p <0.05) that were not different from those in the control group (p> 0.05). Mean levels of group 1 antibodies declined gradually between day 1 and day 45, but remained higher than those of the control group at birth, whereas the values remained stable in group 2. The average level of antibodies increased at day 45 in the control group because 4 foals developed confirmed R. equi pneumonia. However, no significant difference with baseline values was observed in this group excluding foals with pneumonia (p> 0.05).

2.4 The antigenic preparation containing the VapA protein and not that consisting of R. equi total bacteria significantly increases serum opsonizing activity in mares and foals

The 45 ^th day after immunization, serum opsonizing activity was higher in mares Group 1 (average number of adhering bacteria per 200 neutrophils: 238.6 ± 30.6 Figure 4) than those of Group 2 and control group (p <0.001 and p <0.01 respectively); these last 2 groups did not differ for this criterion (p> 0.05). This activity has been transmitted foals; in fact, group 1 foals showed an average number of adherent bacteria per 200 neutrophils (91.48 ± 11) higher than group 2 and control foals (respectively p <0.01 and ρ <0.001). (Figure 4).

2.5 Occurrence of R. equi pneumonia in control foals and from immunized mares

Four of 15 foals in the control group had confirmed R. equi pneumonia and no foal in the other 2 groups, strongly suggesting a protective effect of immunization (p = 0.02).

EXAMPLE 2 PROTOCOL FOR THE PREPARATION OF VACCINE ANTI-R. EQUI INTENDED FOR GRAVID MARGINS (EXTRACTION OF

ANTIGENS AT THE TWEEN)

Bacterial strain: Rhodococcus equi 85F deposited at the CNCM on July 2, 2004 under the number 1-3250.

Culture media: Brain-heart infusion (BHI) pH 6.5

Culture conditions: 37 ° C with stirring (150 rpm), 48-72 hours. End of exponential phase of growth (OD = 0.7, reading at 600 nm).

Antigen extraction: Extraction buffer: 25 mM Tris acetate pH 8.5 0.1% Tween 20

Wash Buffers: 1) Tris acetate 10 mM pH 7-8

2) 25 mM Tris acetate pH 7.5 All buffers are filtered (0.2μm) and stored at 4 ° C

Protocol:

1. After centrifugation (10 000 g, 20 minutes at ^{40 °} C.), the bacterial pellet is washed twice in buffer 1 (5 ml / g of wet bacteria) then once in buffer 2. 2. The bacterial pellet is suspended in the extraction buffer at 37 ^° C. for 90 minutes while stirring in the presence of glass microbeads (150 to 212 μm) and then centrifuged at 100,000 × g for 1 hour at 4 ° C. 3.The supernatant Sl is preserved (antigens) at 4 ^° C. Quality control by protein assay and electrophoresis

A. Preparation of vaccine doses (intramuscular injection, 1 ml)

Adjuvant: IMS 3012 (France SEPPIC ₅₎ Antigen: Sl antigen solution diluted to 1 mg / ml and filtered (0.22 .mu.m)

The adjuvant and the antigen are mixed (vol: vol) and then the mixture is stirred gently for 10 min at ^{40 °} C.

All manipulations are performed under sterile conditions.

Quality control: bacteriological

COMPARATIVE EXAMPLE 3: SURPRISING EFFECT OF TWEEN-20

IN RELATION TO TRITON IN THE PREPARATION OF EXTRACTS

Antigenic

- 24 mares immunized with the adjuvant IMS3012 associated with the antigenic preparation

- 16 test mares who received the adjuvant IMS3012 without the antigenic preparation

The mares of both lots received 3 injections (2 during early foaling).

After the appearance of inflammatory reactions, both in the chest and the neck, it was hypothesized that the antigenic preparation could be at the origin of the reactions. It was decided to modify the preparation of the antigenic extracts by replacing as detergent the newt by Tween-20. The observed results are reported in the table below.

Claims

claims

1. Composition comprising a soluble antigenic extract of bacteria

Rhodococcus equi as a medicament, characterized in that said extract comprises R. equi membrane antigens in solution in an extraction solution containing a polyoxyethylene sorbitan fatty acid ester nonionic detergent.

2. Composition according to claim 1, characterized in that it further contains an immunity adjunct of the nanoparticulate type or oil-in-water emulsion type.

3. Composition according to claim 2, characterized in that the adjuvant of the nanoparticulate immunity is MONTANIDE IMS 3012 ^® .

4. Composition according to claim 3, characterized in that it contains 50% of the soluble antigenic extract and 50% of the nanoparticulate adjuvant MONTANIDE IMS 3012 ^® .

5. Composition according to claim 2, characterized in that the adjuvant of the oil-in-water emulsion type immunity is MONTANIDE ISA 35 ^® .

6. Composition according to claim 5, characterized in that it contains 75% of the soluble antigenic extract and 25% of the adjuvant oil-in-water emulsion MONTANIDE ISA35 ^® .

7. Composition according to one of Claims 1 to 6, characterized in that the polyoxyethylene sorbitan fatty acid ester is chosen from polyoxyethylene sorbitan monolaurate, polyoxyethylene 20 sorbitan, polyoxyethylene sorbitan monostearate, and polyoxyethylene sorbitan monooleate.

8. Composition according to Claim 7, characterized in that the polyoxyethylene sorbitan fatty acid ester is polyoxyethylene monolaurate.

Sorbitan.

9. Composition according to one of claims 1 to 8, characterized in that said nonionic detergent is at a concentration of between 0.01% and 5% volume by volume (v / v) in said extraction solution.

10. Composition according to claim 9, characterized in that the concentration of nonionic detergent is 0.1% v / v in said extraction solution.

11. Composition according to one of claims 1 to 10, characterized in that the Rhodococcus equi bacteria are of strain selected from strains ATCC33701, ATCC6939, ATCC2572, and strain 85F filed at the CNCM July 2, 2004 under the number 1 -3250.

12. The composition as claimed in claim 11, characterized in that the Rhodococcus equi bacteria are of strain 85F deposited at the CNCM on July 2, 2004 under the number 1-3250.

Use of a soluble antigenic extract as defined in any one of claims 1 and 7 to 12 for the preparation of a pharmaceutical composition for preventing or treating R. equi infection in a mammal.

14. Use according to claim 13, characterized in that the mammal is an equine.

15. Use according to claim 13 or 14, characterized in that infection with R. equi induces a disease of the respiratory system, including pneumonia.

16. Use according to one of claims 13 to 15, characterized in that the pharmaceutical composition further comprises an adjuvant as defined in claims 2 to 6.

17. Use according to one of claims 13 to 16, characterized in that the pharmaceutical composition is administered to said mammal by intramuscular or subcutaneous route.

18. Use according to one of claims 13 to 17 for the prevention or pre-natal treatment of a foal in preparation, said pharmaceutical composition being administered to the pregnant mare.

A process for preparing a soluble antigenic extract obtained from Rhodococcus equi bacteria, said method comprising the following steps: a) solubilizing the membranes of said bacteria by contacting these bacteria with an extraction solution containing a nonionic detergent of the polyoxyethylene sorbitan fatty acid ester type, and b) the recovery of the antigenic extract solubilized in step a), characterized in that the Rhodococcus equi bacteria are of 85F strain deposited at the CNCM on 2 July 2004 under the number 1-3250.

20. Preparation process according to claim 19, characterized in that the polyoxyethylene sorbitan fatty acid ester is chosen from polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, and Polyoxyethylene sorbitan monooleate.

21. Preparation process according to claim 20, characterized in that the polyoxyethylene sorbitan fatty acid ester is polyoxyethylene sorbitan monolaurate.

22. Preparation process according to one of claims 19 to 21, characterized in that said nonionic detergent is at a concentration of between 0.01% and 5% volume to volume (v / v) in said extraction solution .

23. Preparation process according to claim 22, characterized in that the concentration of nonionic detergent is 0.1% v / v in said extraction solution.

24. Preparation process according to one of claims 19 to 23, characterized in that in step a) of solubilization, bringing the bacteria into contact with the extraction buffer is carried out at a proportion of 5 ml of said buffer per gram of wet bacteria.

25. Preparation process according to one of claims 19 to 24, characterized in that said bacteria are in the form of a bacterial pellet obtained after centrifugation, before step a).

26. Preparation process according to claim 25, characterized in that one carries out at least one wash of the bacterial pellet in a suitable washing buffer, before step a).

27. Preparation process according to one of claims 19 to 26, characterized in that in step b) the product obtained in step a) is centrifuged, and the centrifugation supernatant containing said solubilized antigenic extract is recovered. .

28. A process for preparing a soluble antigenic extract obtained from Rhodococcus equi bacteria of strain 85F deposited at the CNCM on July 2, 2004 under the number 1-3250, characterized in that said process comprises the following steps: Obtaining a bacterial pellet by centrifugation of said bacteria

Rhodococcus equi suspended at a speed of 10000 g for 20 minutes, preferably at a temperature of ^{40 °} C.

Two successive washes of the bacterial pellet obtained in a 10 mM Tris acetate buffer of pH 7 to 8, followed by a third washing in a buffer

25mM Tris Acetate pH 7.5, Solubilization of the bacterial membranes of the washed bacterial pellet by contacting said pellet with an extraction solution containing polyoxyethylene sorbitan monolaurate at a concentration of 0.1% (v / v). v) in said extraction solution, the bacteria / extraction buffer proportion being 5 ml of said buffer per gram of wet bacteria, said solubilization being carried out with stirring for 90 minutes at a temperature of between 35 and 40 ^° C., and

29. soluble antigenic extract of Rhodococcus equi bacteria obtainable from the method according to one of claims 19 to 28, characterized in that said extract comprises membrane antigens of R. equi strain 85F deposited at the CNCM on 2 July 2004 under the number 1-3250, said antigens being in solution in an extraction solution containing a nonionic detergent of polyoxyethylene sorbitan fatty acid ester type.

Soluble antigenic extract according to claim 29, characterized in that the polyoxyethylene sorbitan fatty acid ester is polyoxyethylene sorbitan monolaurate.