Chemistry: molecular biology and microbiology – Measuring or testing process involving enzymes or... – Involving viable micro-organism
Patent
1996-11-22
1998-07-28
Leary, Louise N.
Chemistry: molecular biology and microbiology
Measuring or testing process involving enzymes or...
Involving viable micro-organism
435 14, 435 18, 435 29, 435 30, 435879, 435822, 435968, 426 48, 426 52, 426 55, 426 42, 426 43, 546152, 436 111, C12Q 104, C12Q 154, C12Q 134, C12Q 102
Patent
active
057861676
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and a culture medium for the identification and distinguishing of Salmonella sp. among other gram-negative bacteria, especially those belonging to the family Enterobacteriaceae, in an analytical sample. The invention is characterized by the features defined in the claims.
2. Description of Related Art
Rapid species identification of infective organisms is important, whether for epidemiology studies, for diagnosis of both human and veterinary diseases, for selecting appropriate medical treatment or for deciding on control measures in the food industry and other segments of environmental hygiene. To prevent outbreaks of food poisoning, food and environmental (water, soil and alike) samples are continuously being monitored especially for the presence of salmonellae.
At least eight different agar-based media for culturing and identification of salmonellae are commercially available today (Difco Manual, 1984, Difco Laboratories, Detroit, Mich., USA). Most of these are based on determination of lactose utilization and/or measurement of hydrogen sulfide production. Since most salmonellae are lactose-negative and thus do not contain .beta.-galactosidase enzyme as most of the other bacteria in the family Enterobacteriaceae do, they can easily be distinguished from many other bacteria on the basis of their .beta.-galactosidase negativity.
The currently used culture media contain various amounts of additives that inhibit the growth of other bacteria; in other words, the media have been made selective so that only salmonellae would grow on them. These media have many limitations, however. Use of inhibitors that prevent the growth of gram-negative bacteria is undesirable, since some inhibitors will, to some extent, prevent even the growth of salmonellae. In other words, such media are too selective and therefore two different media have to be used, one of which is less selective. The more selective culture medium is used for measuring the production of hydrogen sulfide, which alone is not a reliable method because it is sensitive to many external factors, such as oxygen concentration and pH. Furthermore, several strains produce different amounts of hydrogen sulfide. Combining measurement of hydrogen sulfide production with lactose fermentation on a less selective medium is also insufficient to distinguish salmonellae from other bacteria occurring in nature. Since for example Proteus spp. resemble salmonellae in being lactose-negative and in producing hydrogen sulfide, they cannot be distinguished from salmonellae by means of commercial culture media (Difco Manual).
The aforementioned commercial culture media do not allow differentiation among colonies on the basis of appearance, since bacteria form colonies of uniform color on these media. Nevertheless, the recently introduced Rambach agar has been developed with a view to enhancing the distinction of different bacteria directly on the basis of colony color (E. Merck, Darmstadt, Germany). On this agar, Salmonella spp. grow as pink colonies while other bacteria of the family Enterobacteriaceae, e.g., many coliforms, form blue, green, violet, or colorless colonies. This advantage of Rambach agar is based on the ability of .beta.-galactosidase-negative salmonellae to utilize propylene glycol. In the presence of an indicator substance, decomposition of propylene glycol yields a red color, and not blue, for instance. Rambach agar is very specific for all salmonella strains except S. typhi and S. paratyphi. Few false positives are obtained with Rambach agar (Garrick R. G. and A. D. Smith, Letters Appl. Microbiol. 18:187-189, 1994). Still, the method has the disadvantage of not revealing typhi strains.
U.S. Pat. No. 5,434,056 discloses a method for selective detection of salmonella, and a medium for that purpose which contains glucuronic acid or its salts, a pH indicator, a chromogenic compound to distinguish .beta.-galactosidase-positive bacteria from .beta.-galactosidase-negativ
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Abstract of WO 93/23527 A1, Nov. 25, 1993.
Jussila Marita
Laine Irmeli
Scheinin Leena
Tuompo Helena
Leary Louise N.
Orion-Yhtymae Oy
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