GB2106539A - Bacteriological MPN strip - Google Patents

Abstract

This invention is a convenient device for the enumeration of micro- organisms in liquids or suspensions. It consists of a plastic screw capped container having septa, for the division of the sample into appropriate volumes, and Durham tubes moulded in. It contains a sterile growth medium in lyophilised, powder or tablet form. The container is aseptically filled with sample to a line marked on its side, agitated to dissolve the medium and layed flat on a plane surface. It is then rotated through 90 DEG about its long axis so that the desired volumes of sample are separated into their respective compartments. The Durham tubes are designed so that air escapes from them during this operation. Incubation may begin immediately using a portable incubator if necessary. The device was conceived with potable water bacteriology in mind but many other possible applications exist.

Description

**WARNING** start of DESC field may overlap end of CLMS **.

SPECIFICATION Bacteriological M.P.N. strip Technical field Bacteriology State of art HMSO report 71, 'The Bacteriological Examination of Water Supplies'.

Freshwater Biological Association, 'A guide to methods for estimating Microbial Numbers and Biomass in fresh water.

Medical Microbiology: Cruikshank

Description The invention is a device for the quantitative estimation of microorganisms in liquids. The number of organisms present in solid substances may also be estimated by suspension or dissolution of the substance in an appropriate diluent or solvent. As described the device may only be used for low concentrations of microorganisms, however, by dilution of the substance under test in a suitable diluent the range may be extended.

The device combines the function of sample container and most probable number of (M.P.N.) estimation apparatus. It is constructed in transparent plastic or glass and contains an appropriate sterile lyophilised, powdered, liquid or tablet form growth medium. Durham tubes for the detection of gas and septa, for the division of the sample under test into the required volumes, are moulded into the implement which has a screw cap for the addition of the sample.

The novel method of performing an MPN test, involves first filling the strip in a vertical position to a mark then agitating to dissolve and mix the growth medium. The strip is then layed flat on a horizontal surface and lifted to an upright position by a rotational movement pivoting on the appropriate long lower edge of the device. This movement separates the sample mixed with growth medium into one 50 ml, five 10 ml and five 1 ml volumes (or other appropriate volumes) due to the position of dividing septa.

The medium employed in the device depends on the organism or group of organisms to be enumerated. Selective or non selective growth media with or without indicator substances in a form previously mentioned may be employed as in conventional MPN tests.

In field tests incubation may begin immediately in a mobile incubator or alternatively upon return to the laboratory. During transport from the field the height of the dividing septa obviates any cross contamination between the compartments.

After incubation for an appropriate time, colour changes and gas production may be observed within the compartments. The wedge shape of the Durham tubes serves two function: firstly to allow the escape of gas in the horizontal position before rotation to the vertical and secondly so that the prism effect of the wedge full of gas causes the optical distortion of a line marked on the implement facilitating visual observation of gas production. Detection of colour changes and gas production may also be achieved by one or more photoelectric devices operating inside a specialised incubator.

The concentration of organisms present in the original sample is deduced, from the combination of positive and negative compartments, by reference to the standard MPN tables published in many relevant books, or obtained automatically by an appropriately programmed microprocessor and display device connected to the automated photoelectric sensor(s). Allowance must be made for dilution and for the ratio of solid material to diluent in the case of solids estimations.

Samples of investigative or confirmatory tests can be obtained by means of a sterile disposable hypodermic syrings or other sharp device which will penetrate the plastic material employed.

The device avoids the need for sample bottles, incubation bottles, test tubes, Durham tubes, test tube caps, pipettes, pipette cases, autoclaves, sterilising ovens and highly trained technicians in the laboratory and hence has great potential for application in developing countries. In developed countries where technicians and scientists are available the implement will allow savings in time and equipment.

Applications for the device exist in the field of water microbiology, food microbiology, medical and veterinary microbiology and industrial microboilogy. Organisms which can be enumerated are predominantly bacteria but include fungi, algae, protozoa and viruses.

Claims (filed on 8-9-82) 1. The invention is a device for estimating the Most Probable Number (MPN) of microorganisms in a liquid or suspension by means of a single receptacle containing a sterile growth medium. The construction of the receptacle enables the division of a sample, by moulded septa, into the volumes required for an MPN estimation by a series of simple manipulations requiring no other apparatus.

2. The shape of the optional incorporated Durham tubes allows for the escape of air during the sample proportioning manipulations.

Claims (2)

SPECIFICATION Bacteriological M.P.N. strip Technical field Bacteriology State of art HMSO report 71, 'The Bacteriological Examination of Water Supplies'. Freshwater Biological Association, 'A guide to methods for estimating Microbial Numbers and Biomass in fresh water. Medical Microbiology: Cruikshank Description The invention is a device for the quantitative estimation of microorganisms in liquids. The number of organisms present in solid substances may also be estimated by suspension or dissolution of the substance in an appropriate diluent or solvent. As described the device may only be used for low concentrations of microorganisms, however, by dilution of the substance under test in a suitable diluent the range may be extended. The device combines the function of sample container and most probable number of (M.P.N.) estimation apparatus. It is constructed in transparent plastic or glass and contains an appropriate sterile lyophilised, powdered, liquid or tablet form growth medium. Durham tubes for the detection of gas and septa, for the division of the sample under test into the required volumes, are moulded into the implement which has a screw cap for the addition of the sample. The novel method of performing an MPN test, involves first filling the strip in a vertical position to a mark then agitating to dissolve and mix the growth medium. The strip is then layed flat on a horizontal surface and lifted to an upright position by a rotational movement pivoting on the appropriate long lower edge of the device. This movement separates the sample mixed with growth medium into one 50 ml, five 10 ml and five 1 ml volumes (or other appropriate volumes) due to the position of dividing septa. The medium employed in the device depends on the organism or group of organisms to be enumerated. Selective or non selective growth media with or without indicator substances in a form previously mentioned may be employed as in conventional MPN tests. In field tests incubation may begin immediately in a mobile incubator or alternatively upon return to the laboratory. During transport from the field the height of the dividing septa obviates any cross contamination between the compartments. After incubation for an appropriate time, colour changes and gas production may be observed within the compartments. The wedge shape of the Durham tubes serves two function: firstly to allow the escape of gas in the horizontal position before rotation to the vertical and secondly so that the prism effect of the wedge full of gas causes the optical distortion of a line marked on the implement facilitating visual observation of gas production. Detection of colour changes and gas production may also be achieved by one or more photoelectric devices operating inside a specialised incubator. The concentration of organisms present in the original sample is deduced, from the combination of positive and negative compartments, by reference to the standard MPN tables published in many relevant books, or obtained automatically by an appropriately programmed microprocessor and display device connected to the automated photoelectric sensor(s). Allowance must be made for dilution and for the ratio of solid material to diluent in the case of solids estimations. Samples of investigative or confirmatory tests can be obtained by means of a sterile disposable hypodermic syrings or other sharp device which will penetrate the plastic material employed. The device avoids the need for sample bottles, incubation bottles, test tubes, Durham tubes, test tube caps, pipettes, pipette cases, autoclaves, sterilising ovens and highly trained technicians in the laboratory and hence has great potential for application in developing countries. In developed countries where technicians and scientists are available the implement will allow savings in time and equipment. Applications for the device exist in the field of water microbiology, food microbiology, medical and veterinary microbiology and industrial microboilogy. Organisms which can be enumerated are predominantly bacteria but include fungi, algae, protozoa and viruses. Claims (filed on 8-9-82)

1. The invention is a device for estimating the Most Probable Number (MPN) of microorganisms in a liquid or suspension by means of a single receptacle containing a sterile growth medium. The construction of the receptacle enables the division of a sample, by moulded septa, into the volumes required for an MPN estimation by a series of simple manipulations requiring no other apparatus.

2. The shape of the optional incorporated Durham tubes allows for the escape of air during the sample proportioning manipulations.

**WARNING** end of CLMS field may overlap start of DESC **.