MANNITOL LYSINE AGAR

Description

Human Salmonella infections are most commonly caused by ingestion of food, water or milk contaminated by human or animal excreta. One of the most important criteria in the identification of Salmonella species is the production of hydrogen sulphide. Salmonella Typhi and Salmonella Paratyphi A can be differentiated from the rest of the Salmonella due to their inability to form hydrogen sulphide. Mannitol Lysine Agar, formulated as described by Inoue et al is used for the selective isolation of Salmonella species other than Salmonella Typhi and Salmonella Paratyphi A form different foods and faeces. Mannitol Lysine Agar may be used directly with the specimen or from an enrichment culture. Enrichment can be carried out in Modified Semisolid RV Medium. Mannitol Lysine Agar does not depend upon lactose fermentation and is therefore recommended for investigating lactose fermenting Salmonellae like Salmonella Arizonae. Further tests should be carried out for confirming Salmonella species. Mannitol Lysine Medium should be used in conjunction with Brilliant Green Agar, Modified or Bismuth Sulphite Agar. Mannitol Lysine Medium can be directly inoculated with the specimen or the specimen can be first enriched in Modified Semisolid RV Medium Base. Atypical Salmonella will form a characteristic bulls eye due to less H2S production, which gets concentrated in the centre of the colony. Salmonella colonies will form purple black colonies. Presumptive Salmonella should be confirmed by biochemical tests.