I´m doing some analyses to fruit juices and soft drinks. I was enumerating the lacobacillus by spread plate in MRS agar at 37 ºC in anaerobiosis. Now, we don´t have an anaerobic incubator, so I have to use aerobic conditions. In MRS at 37 ºC at aerobioses conditions i was using the catalase test to descriminate between the lactic acid bacteria and yeast colonies.
Do you think, If i put the plates in anaerobiosis the yeast growth can be inhibited?
Or maybe if I add cycloheximide to MRS agar, i can suppress yeast growth and do not have to do additional tests...
Hello Barbara,
Anaerobic growth of yeast is limited without ergosterol addition, however MRS contain some yeast extract (5g/L I think...) so you may have some yeast growth.
You can try to put the plate under anaerobic condition (using anaerobic jar with anaerocult for example) and compare with aerobic condition.
You wan also try the addition of an antifungal compound (such as Nystatin - 5 to 10 μg/ml) in the MRS agar.
Regards
Hi Barbara,
Beside what Cyril has mentioned, i usually smell the agar plate and the yeast smell is very much distinguished. However, you can also do simple Gram-staining where the differences between both microorganisms are remarkably clear.
I was thinking in add cycloheximide to MRS agar, I think that the function is similar to Nystatin. However because of it toxicity I am with doubts in using this compound. Is nystatin toxic too?
I thought that using anaerobic conditions I could suppress yeast growth, however i think that i have to choose between using an antifungal compound or doing more tests.
Sarika,
In what concentration can I use sorbic acid to control the yeast growth?
The nynastin is not toxic for human (it is preconised for candida infection) and is produced from bacteria (a pseudomonas if i remeber well...)
So it would be toxic... but only for your yeasts.
Regards.
I work with silage samples that contain many types of microorganismes. I use vancomycine to count only LAB.
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