Yersinia Selective Agar Base, w/ 1.2% Agar

Principle And Interpretation

Yersinia Selective Agar Base, w/ 1.2% Agar is formulated, for the isolation of Yersinia from food specimens in accordance with FDA BAM, 1998 (1). Yersinia species have been reported to be responsible for yersiniosis, a range of diseases/ syndromes from gastroenteritis to plague. The organism is transmitted by ingestion of contaminated food (often milk and pork) and water, probably by the fecal-oral route or through contact with infected animals (2,3). The mechanisms of pathogenicity in the enteropathogenic Yersinia are complex and have served as research models for understanding the infectious process in many enteropathogenic bacteria. Food samples with suspected Yersinial contamination are processed for the bacterial isolation using respective selective agars. According to the BAM protocol, aseptically weigh 25g sample into 225 ml Peptone sorbitol Bile Broth (M1231). Homogenized samples are incubated for 10 days at 10°C. If high levels of Yersinia are suspected, spread plate of 0.1ml each are done on MacConkey Agar (M081D) and Yersinia Selective Agar Base, w/ 1.2% (M843F) before incubation of the broth. Also transfer 1 ml homogenate to 9 ml 0.5% KOH in 0.5% saline (4), mix for 2-3 seconds, and spread-plate 0.1 ml on MacConkey and CIN agars. Incubate agar plates at 30°C for 1-2 days. Repeat this on day 10 as well. Yersinia colonies on Yersinia Selective Agar Base, w/ 1.2% appear as deep red center with sharp border surrounded by clear colorless zone with entire edge and on MacConkey, they appear as flat, colorless, or pale pink colonies. Colonies isolated have to be confirmed through biochemical and serological assays.

Peptone and yeast extract provide nitrogenous and carbonaceous compounds, long chain amino acids and other essential compounds. Mannitol is the energy source. Sodium deoxycholate inhibits the growth of most of the non-enteric organisms. Magnesium sulphate provides essential ions and sodium chloride maintains the osmotic equilibrium of the medium. Neutral red and crystal violet acts as the indicators and agar as the solidifying agent.