IE900154A1 - Anti-microbial agent - Google Patents

Abstract

Glutaraldehyde is a useful anti-microbial agent, but is dangerous and unpleasant to handle and is thermally unstable. Despite these disadvantages, it is specified for use against bacteria in cooling towers of air conditioning plants of buildings and to control anaerobic sulphate-reducing bacteria in oil wells. The invention provides the bisulphite addition complex of an aldehyde or di-aldehyde, for use as an anti-microbial agent. The complex is less toxic than free glutaraldehyde. In cooling towers it slowly oxidises to the free di-aldehyde. In oil wells, its digestion by the sulphate-reducing bacteria releases the free di-aldehyde which controls the bacteria. In these ways, a more economic and environmentally safer use of anti-microbial additives is likely

Description

ANTI-MICROBIAL AGENT Technical Field This invention relates to anti-microbial agents and, more particularly, to such agents and their use to control bacteria in such locations as the cooling towers of the air conditioning systems of large buildings, anaerobic fluids in oil wells, and water-based slurries in industrial process plant.

Background Art 1,5-Pentanedial (commonly known as glutaraldehyde) is 10 known for use as a disinfectant. Proprietary compositions include BASF's PROTECTOL (Trade Mark) and Union Carbide's AQUCAR (trade Mark). Essentially, these products are aqueous solutions of glutaraldehyde. They are used in particular to control growth of bacteria in cooling towers, and the anaerobic bacterium Desulfovibrio desulfuricans in oil well environments.

Glutaraldehyde is, however, relatively reactive and so is liable to lose effectiveness unless stored and used in particular ways, As temperature rises above about 30°C or pH above about 7 it is liable to polymerise. In the hot environment of an oil well this loss of effectiveness is a serious problem and expense.

Uncontrolled release of glutaraldehyde at high concentration is undesirable because it is biologically so harmful. In situations where release of pollutants is strictly controlled, therefore, glutaraldehyde can only be used with extreme care.

It is an object of the present invention to provide the anti-microbial effectiveness of glutaraldehyde more IE 90154 - 2 economically and with reduced risk of environmental damage .

Summary of the Invention According to a first aspect of the invention there is provided a bisulphite addition complex of an aldehyde or di-aldehyde, for use as an anti-microbial agent.

According to a second aspect of the invention there is provided a method of controlling the growth of bacteria at a particular site by introducing to the site a bisulphite addition complex of an aldehyde or di-aldehyde.

The site may be, for example, a body of water in the cooling tower of an air conditioning system of a building. In such a case it may be convenient to add the addition complex as an aqueous solution, so the aldehyde or di-aldehyde complex should be water-soluble. Including a surfactant may assist contact between the complex and the organisms to be combated. The action of the cooling tower brings the water into intimate contact with atmospheric oxygen, which oxidises the complex to release the aldehyde or di-aldehyde which is thereby available in the body of water to disinfect it. As shown below, the addition complex has proved effective in controlling Legionella pneumophila .

The site may instead be within an oil well, where the presence of Desulfovibrio desulfuricans is a problem. Tests conducted by the Applicants have established the effectiveness of the bisulphite complex in combating this bacterium. It may be that 'Desulfovibrio desulfuricans utilises the sulphite content of the complex as a terminal electron acceptor and, in so doing, liberates the aldehyde or di-aldehyde which is effective then to kill the bacterium. Conventionally, glutaraldehyde is used to control this bacterium. As a di-aldehyde its addition complex has two bisulphite groups, both of which have to IE 90154 - 3 be utilised by the bacterium before the uncomplexed aldehyde is released. Effectiveness may depend on the availability to the bacterium of the sulphite in the addition complex relative to that of the sulphite in the oil, which it would utilise in the absence of the addition complex.

In a similar way, the bisulphite addition complex can be used in slurries of ground calcium carbonate as are used in the paper trade as a filler. These products are frequently contaminated with Desulfovibrio desulfuricans, to become objectionable slurries smelling highly of hydrogen sulphide and similar noxious products. Addition of the complex provides protection from this effect at very low concentrations. It is therefore relatively economic and yet effective over a long period of time, with very little adverse effect on the slurry and its uses compared to the addition of other conventional bactericides .

In all these applications, it is valuable that the addition complex is thermally more stable than the uncomplexed aldehyde or di-aldehyde, and less likely to polymerise. The cooling tower oxidation acts as a slow release machanism, of uncomplexed biocide from dissolved complex in the water body. In the oil well situation, the complex may remain indefinitely, to police bacterial growth, being consumed only when sulphate reducing bacteria are present and utilising it. Thus, it is likely that less of the anti-microbial agent will be consumed, and that its replenishment need take place less frequently. Initial concentrations will tend to be less, and there is much less prospect of pollution damage if there is a release of the fluid containing the anti-microbial agent.

Description of Preferred Embodiments Aldehyde bisulphite complexes were made by the following IE 90154 - 4 method.

Sodium metabisulphite in the required quantity was dissolved in water and its temperature brought to 40 °C. Aldehyde as required was added and the mixture stirred for one hour. Each mixture became homogeneous over the course of the hour and was assumed to have reacted completely. Individual experiments are shown in Table 1 below. Because benzaldehyde is of limited solubility it was reacted at 50°C. After one reacted. hour most of the benzaldehyde had The invention is illustrated by the following Examples. EXAMPLE 1 The anti-microbial activity of the bisulphite complex of the aldehydes in Table 1 at 35 °C was examined by incubating test tubes, inoculated at zero time with sulphate reducing bacteria, and monitoring the extent of bacterial cell growth with time.

The bacterial inoculant was a culture of Desulfovibrio desulfuricans (NCIB 8307) grown and inoculated at 35°C in anaerobic conditions in Postgates medium. The composition of this medium is given below in Table 2.

Test tubes were prepared in groups of three. Each control tube contained 20mls of a mixture of Postgates medium and a saline reductant ( 9g NaCl and 0.lg sodium thioglycollate per litre of distilled water).

Each tube exemplifying the invention also contained, in the 20ml charge, one or other of the bisulphite complexes of Table 1, at a concentration of 100, 1000 or 5000mg/litre.

The inoculated tubes were examined daily for bacterial growth as evidenced by blackening of the growth medium.

IE 90154 - 5 The Most Probable Numbers (MPN) method provides a basis for a quantitative assessment of the numbers of sulphate reducing bacteria present at any particular time. In Table 3, the results are shown for each test tube monitored, growth being signified by (+) and the absence of growth by (-). The individual anti-microbial agent is identified by the abbreviation used in Table 1, suffixed B when the bisulphite complex was used.

EXAMPLE 2 The anti-microbial action of the bisulphite complexes of Table 1 against a yeast (Saccharomyces cerevisiae), a gram positive bacterium (Streptococcus faecalis) and a gram negative bacterium (Escherichia coli) and at a concentration of 5000mg/l was examined by inoculation into cell cultures in test tubes at time 0, followed by incubation with continuous shaking of estimation of cell numbers after 5hrs results are shown in Table 4, expressed as a percentage reduction in the initial concentration of bacteria cells. and The the tubes, and 24hrs.

EXAMPLE 3 A glutaraldehyde complex was compared with straight glutaraldehyde with an without air oxidation using the minimum inhibitory concentration test (MIC) following the German guidelines and recommendations as applied by Kelsey and Sykes. Tests were carried out against Legionella bacteria and Pseudomonas specie using the following media cultures . 1. Pseudomonas fluorescens - Muellor Hinton Broth 2. Legionella pneumophila - Muellor Hinton Broth with Legionella C7E base and supplement.

The dilution tubes were incubated at room temperature for Pseudomonas and 35°C for Legionella pneumophila. All tubes were unshaken.

IE 90154 - 6 The results of the tests are set out in Table 5 below. Bacterial growth is signified by (+) and absence of growth by (-).

The effect of glutaraldehyde complex on the viability of Pseudomonas fluorescens in water and enrichment broth under conditions of air oxidation was next examined. For the results obtained see Table 6 below, in which the upper half of the table relates to water amd the lower half to enrichment broth. Strong growth is indicated by (+++), weak growth by (+) and absence of growth by (-).

EXAMPLE 4 Mueller-Hinton broth medium absorbs biocidal chemical medium. Any reduction in growth in a bacteriostatic test would indicate an active biocide. Thus, where only small colonies are noted, in a case of a large initial concentration of cells, inhibition of growth is indicated, and thus as active biocide.

Starter broth cultures grown overnight at 35° were diluted in distilled water. Gram negative (Escherichia coli) and Gram positive (Streptococcus faecalis) test organism cultures were diluted 1:100 and 1:10,000 and plated on to Mueller Hinton medium containing various stated concentrations (mg/1) of specified biocides. The spread plates were incubated at 35°C. The Escherichia coli plates were read after 1 day and the Streptococcus faecalis plates after 3 days. The results are set out below in Table 7. In the Table, the indicia used in earlier Tables have the same meaning. NN means too numerous to count. W means weak growth and WW extremely weak growth.

The Table shows strong inhibition of growth of Streptococcus faecalis by the glutaraldehyde and benzaldehyde bisulphite complex and good, but less strong, inhibition of growth of Escherichia coli. The other anti-microbial agents has an inhibitory effect, but not so IE 90154 - 7 pronounced.

INDUSTRIAL APPLICATION The bisulphite complex of a low molecular weight aldehyde or di-aldehyde is easier to handle, and less toxic, than the corresponding free aldehyde or di-aldehyde. Its accidental release causes less environmental damage, and it is more thermally stable and resistant to polymerisation. Yet it can be at least as effective as the free aldehyde or di-aldehyde as an anti-microbial agent, in that it will readily release the free aldehyde for biocidal action, for example by oxidation or by the action of the microbe itself on the aldehyde complex. It may therefore be possible to achieve anti-microbial effects comparable with existing glutaraldehyde treatment regimes, but at lower consumption of the anti-microbial agent.

The rate of release of the biocide into, for example, a body of water in a cooling tower will generally be over a period of time determined by the rate of oxidation of the bisulphite complex. The rate of oxidation can be controlled by, for example, the vigour and intimacy with which the water is mixed with ambient air. Thus, in aiming for an optimum use of the present bisulphite agents, a more precise specification of cooling tower construction and operation may result.

Normally, the sodium or potassium addition complex is employed, and normally the aldehyde or di-aldehyde is chosen so as to yield a water-soluble bisulphite addition complex of wide utility, which is cheap to manufacture and easy to use.

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Claims (6)

1. For use as an anti-microbial agent a bisulphite addition compound of an aldehyde or di-aldehyde.

2. An anti-microbial composition, characterised in that it contains, as an active ingredient, a bisulphite 5 addition compound of an aldehyde or di-aldehyde.

3. A composition as claimed in claim 2 wherein the aldehyde or di-aldehyde comprises glutaraldehyde.

4. A composition as claimed in claim 2, wherein the aldehyde or di-aldehyde comprises benzaldehyde. 10 5. A composition as claimed in claim 2, 3, or 4 characterised by the presence of a surfactant. 6. A method of controlling the growth of bacteria in a body of fluid comprising the step of adding to the fluid a quantity of a bisulphite addition compound of an aldehyde 15 or di-aldehyde. 7. A method according to claim 6, wherein the fluid is water contained within a conditioning plant. cooling tower of an air 8. A method according to claim 6, wherein the fluid is a water-based slurry within process . an industrial manufacturing 9. A method according to claim 6, fluid is in an anaerobic environment. wherein the body of 10. A method according to claim 9, wherein the body of fluid is at the bottom of a well. IE 90154 - 15 11. A method according to claim 10, wherein the body of fluid is at the bottom of a well from which a petroleum product is being won. 12. An anti-microbial composition substantially as

5. Described in the Examples. 13. A method of controlling the growth of bacteria in a body of fluid according to Claim 6 substantially as herein described. 14. The features described in the foregoing

6. 10 specification, or any obvious equivalent thereof, in any novel selection.