One of my colleague trying to isolate Streptococcus thermophillus which is obtained from curd. She faces difficult to isolate the strain. Please anyone could give the suitable procedure or process to isolate the strains. What may be the suitable media to grow and isolate it?
Your colleague might find this introduction useful- https://www.dairyscience.info/index.php/cheese-starters/250-isolating-lab.html. Perhaps the results from a recent student project might also help, please see https://www.dairyscience.info/index.php/student-projects.html .
I have found ST agar ( F.M. Driessen, J. Ubbels, J. Stadhouders, Biotechnol. Bioeng., 19, 821 (1977)) incubated at 44C for 24-48 hours useful. Note the use of sucrose.
Traditional microbiology has lots of limitations when used to isolate wild strains of LAB.
M17 medium indeed is suitable for S. thermophilus isolation from dairy products. As lactose is the preferred sugar of S. thermophilus, use M17 lac (10g/L) plates and incubate at 37-42°C in anaerobic jars (Anaerocults), if possible. When making liquid cultures, don't shake them, and carefully homogenize the culture tubes when sampling. It "should" work!
Regards
It can be challenging is to isolate Str thermophilus from an environment containing lactococci and other bacteria. So some selective pressure is needed. The replacement of lactose by sucrose can help in conjunction with elevated incubation temperatures. While M17 is an excellent medium it is not selective. If you decide to use M17 consider making up your medium from the base ingredients and consider reducing the glycerophosphate concentration by 50%.
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