Novel method based on chromogenic media for discrimination and selective enumeration of XXXX bacteria in fermented milk products.

@entity10264 @entity2176 @entity10547 @entity10263 @entity6330 @entity880 @entity6983 @entity5858
Microbial analyses of fermented milk products require selective methods to discriminate between close species simultaneously present in high amounts. A culture-based method combining novel chromogenic agar media and appropriate incubation conditions was developed to enumerate @entity880 bacteria (LAB) strains in fermented milk. M1 agar, containing two chromogenic substrates, allowed selective enumeration of @entity10263 , two strains of @entity10264 and @entity5858 based on differential b-galactosidase and b-glucosidase activities. Depending on the presence of some or all of the above strains, M1 agar was supplemented with @entity10547 or @entity2176 and incubations were carried out at 37    C or 44    C to increase selectivity. A second agar medium, M2, containing one chromogenic substrates was used to selectively enumerate b-galactosidase producing @entity6330 at 47    C. By contrast with the usual culture media, the chromogenic method allowed unambiguous enumeration of each species, including discrimination between the two @entity6983 , up to 10(9)  CFU/g of fermented milk. In addition, the relevance of the method was approved by enumerating reference ATCC strains in pure cultures and fermented milk product. The method could also be used for enumerations on non-Danone commercial fermented milk products containing strains different from those used in this study, showing versatility of the method. To our knowledge, this is the first description of a chromogenic culture method applied to selective enumeration of LAB.
