15. Evaluation of modified MRS media for the selective enumeration of Lactobacillus casei
Abstract
Lactobacillus is an extensive group of Gram-positive, catalase negative and non-spore forming organism belongs to Lactobacillaceae family. L. casei is an obligate fermentative bacterium with complex nutritional requirements. It has its novel importance as a bio-preservative agent and enhancing food quality. Lactobacillus casei is Generally Recognized as Safe (GRAS). For the isolation and identification, cultural media is one of the most important tools and the methods to distinguish between Lactobacillus casei and Lactobacillus lactis are based upon various biochemical tests. In general, MRS media is used for the isolation of Lactobacillus species but we have developed the modified selective medium that utilizes the calcium gluconate. Modified media involves a pH indicator, differences in pH can be observed by means of detectable color change. An intervention study was conducted to confirm the capability of modified MRS medium to detect L. casei and L. lactis recovered from dairy samples. We were able to enumerate circular medium sized predominant yellowish colored colonies morphologically similar to Lactobacillus casei while the growth of Lactobacillus lactis was inhibited. These colonies were then subjected to PCR to identify L. casei.
Keywords: GRAS; L. casei; L. lactis; MRS; PCR
