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Principle
- Kenner-Faecal (KF) Medium was developed by Kenner et al (1960 & 1961) for detecting Streptococci in water and food materials. KF Streptococcus Agar Base is recommended by APHA for enumerating faecal Streptococci in food materials (2015).
- Media is composed of special peptone, yeast extract, sodium chloride, sodium glycerophosphate, maltose, lactose, sodium azide, and agar. Special peptone and yeast extract provide nitrogen, carbon, amino acids, vitamins and trace ingredients essential for the growth of faecal Streptococci.
- Sodium chloride maintains osmatic balance. Lactose and maltose are fermentable carbohydrates and therefore serve as energy sources. Sodium azide is a selective agent, which hampers the growth of gram-negative bacteria. Sodium glycerophosphate is a buffering agent.
- The media can be fortified with 2,3,5-Triphenyl Tetrazolium Chloride, which is reduced to insoluble formazan by actively metabolizing cells, resulting in the formation of pink or red colonies.
- The acidity caused due to metabolic reaction, changes the color of the indicator dye (Bromo cresol purple) to yellow. Bacterial cells reduce TTC to insoluble formazan, resulting in the formation of pink to red colonies.
- After this presumptive identification, further confirmatory tests should be carried out on selective media.
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