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

Novel method based on chromogenic media for discrimination and selective enumeration of lactic acid bacteria in fermented milk products. Food Microbiol. 2016 May;55:86-94 Authors: Galat A, Dufresne J, Combrisson J, Thépaut J, Boumghar-Bourtchai L, Boyer M, Fourmestraux C Abstract 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 lactic acid bacteria (LAB) strains in fermented milk. M1 agar, containing two chromogenic substrates, allowed selective enumeration of Lactobacillus rhamnosus, two strains of Lactobacillus paracasei subsp. paracasei and Streptococcus salivarius subsp. thermophilus based on differential β-galactosidase and β-glucosidase activities. Depending on the presence of some or all of the above strains, M1 agar was supplemented with l-rhamnose or vancomycin 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 β-galactosidase producing Lactobacillus delbrueckii subsp. bulgaricus at 47 °C. By contrast with the usual culture media, the chromogenic method allowed unambiguous enumeration of each species, including discrimination between the two L. paracasei, up to 10(9) C...
Source: Food Microbiology - Category: Food Science Authors: Tags: Food Microbiol Source Type: research