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Principle
- Tergitol 7 agar base is composed of proteose peptone, yeast extract, lactose, tergitol 7, bromothymol blue, and agar. Protease peptone provides nitrogen and amino acids.
- Yeast extracts serve nitrogen, carbon, and vitamin. Lactose is a fermentable carbohydrate. Tergitol 7 is a selective agent that eases the recovery of injured coliforms. Brom thymol bule is a pH indicator.
- Lactose fermenting microorganisms like Escherichia coli form yellow color colonies with yellow zone, while Enterobacter and Klebsiella colonies are greenish-yellow, and lactose non-fermenting organisms, such as Salmonella and Shigella, produce colonies surrounded by blue zones.
- For more differentiation triphenyltetrazolium chloride is added to the medium, which serves as an indicator of lactose fermenting and non-fermenting bacterial growth. Triphenyltetrazolium chloride is rapidly reduced to insoluble red formazan by most lactose-fermenting organisms except Escherichia coli, Enterobacter, and Klebsiella species.
- While other lactose fermenters, like coliforms, produce greenish-yellow colonies with yellow zones.
- The lactose non-fermenters produce red colonies surrounded by blue zones. Agar is a solidifying agent. The media can be fortified with Penicillin G (1.0 μg/ml), aseptically added to the medium after autoclaving, to prevent the growth of gram-positive cocci.
- The fecal coliform bacteria are identified as yellow colonies with deep yellow halo after incubation at 44°C.
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