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M-RTLV agar, a novel selective medium to distinguish Lactobacillus casei and Lactobacillus paracasei from Lactobacillus rhamnosus

2010; Elsevier BV; Volume: 139; Issue: 3 Linguagem: Inglês

10.1016/j.ijfoodmicro.2010.03.019

1879-3460

Takafumi Sakai, Kenji Oishi, Takashi Asahara, Toshihiko Takada, Norikatsu Yuki, Kazumasa Matsumoto, Koji Nomoto, Akira Kushiro,

Gut microbiota and health

We developed a novel selective medium, modified-rhamnose-2,3,5-triphenyltetrazolium chloride-LBS-vancomycin agar (M-RTLV agar), that utilizes the fermentability of l-rhamnose to distinguish Lactobacillus casei and Lactobacillus paracasei from Lactobacillus rhamnosus. Whereas L. casei and L. paracasei formed red colonies on the M-RTLV agar, L. rhamnosus formed either pink-toned colonies or white colonies with a red spot. An intervention study was conducted to confirm the capability of M-RTLV agar to detect ingested L. casei when recovered from human feces. Subjects consumed one bottle daily of a fermented milk product (Yakult® or Yakult® Light, which contains L. casei strain Shirota; LcS) for 7 days. Diluents of the fecal samples were cultivated on M-RTLV agar. We were able to enumerate circular medium-sized red colonies, which were morphologically similar to L. casei/L. paracasei but clearly distinguishable from the remaining colonies owing to the color difference. These colonies were then subjected to enzyme-linked immunosorbent assay in order to identify the LcS. The viable counts of LcS were 6.6 ± 0.7 log10 CFU/g feces after intake of Yakult® and 6.5 ± 0.6 log10 CFU/g feces after intake of Yakult® Light (mean ± SD).