title: Novel method based on chromogenic media for discrimination and selective enumeration of lactic acid bacteria in fermented milk products.
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) 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.
authors.affiliation: Danone Research Centre Daniel Carasso, RD 128 Avenue de la Vauve, 91700 Palaiseau Cedex, France. Electronic address: anna.galat@danone.com.
authors.forename: Anna
authors.initials: A
authors.lastname: Galat
authors.affiliation: bioMérieux: route de Dol, 35270 Combourg, France. Electronic address: jerome.dufresne@biomerieux.com.
authors.forename: Jérôme
authors.initials: J
authors.lastname: Dufresne
authors.affiliation: Danone Research Centre Daniel Carasso, RD 128 Avenue de la Vauve, 91700 Palaiseau Cedex, France. Electronic address: jerome.combrisson@biomerieux.com.
authors.forename: Jérôme
authors.initials: J
authors.lastname: Combrisson
authors.affiliation: bioMérieux: route de Dol, 35270 Combourg, France. Electronic address: jerome.thepaut@biomerieux.com.
authors.forename: Jérôme
authors.initials: J
authors.lastname: Thépaut
authors.affiliation: Danone Research Centre Daniel Carasso, RD 128 Avenue de la Vauve, 91700 Palaiseau Cedex, France. Electronic address: leyla.boumghar-bourtchai1@danone.com.
authors.forename: Leyla
authors.initials: L
authors.lastname: Boumghar-Bourtchai
authors.affiliation: Danone Research Centre Daniel Carasso, RD 128 Avenue de la Vauve, 91700 Palaiseau Cedex, France. Electronic address: mickael.boyer@danone.com.
authors.forename: Mickaël
authors.initials: M
authors.lastname: Boyer
authors.affiliation: Danone Research Centre Daniel Carasso, RD 128 Avenue de la Vauve, 91700 Palaiseau Cedex, France. Electronic address: candice.fourmestraux@danone.com.
authors.forename: Candice
authors.initials: C
authors.lastname: Fourmestraux
mesh_terms: D000818:Animals; D002417:Cattle; D015169:Colony Count, Microbial; D003470:Culture Media / Q000737:chemistry / Q000378:metabolism*; D043302:Cultured Milk Products / Q000382:microbiology; D005285:Fermentation; D005516:Food Microbiology / Q000295:instrumentation / Q000379:methods*; D007777:Lactobacillaceae / Q000254:growth & development / Q000378:metabolism*; D008892:Milk / Q000382:microbiology*
chemical_list: D003470:Culture Media
keywords: Chromogenic agar; Fermented milk; Food analytical microbiology; Lactic acid bacteria; Strain discrimination; Strain enumeration