Dear researchers,
Recently, I have been facing mysterious test results. I was collecting samples of probiotic cultures from a large fermenter tank into 100mL lab bottle under sterile conditions, the sample was subjected for E.coli testing and showed positive results in MacConkey broth. However, when the same culture collected from the same tank next day into another lab bottle showed negative results in MacConkey broth. The same problem happened for almost 2 months.
Did anyone experience it before or does anyone have an idea why it is happening?
Thanks.
Hi,
What is the level of the contamination ? How many CFU of E. coli did you have ? How many plates of Mc Conckey for each testing ? Which volume of culture did you spot on ?
Contamination can be discontinuous, esp. per Damien's questions, when present at lower levels. I'll ask another question - have you confirmed apparent growth in MacConkey broth is indeed E. coli? And assuming presence of E. coli is out of spec. to what purpose are you retesting?
Hi
The probiotic bacteria can inhibition of coliform bacteria,after day , The probiotic were produce more inhibitor eg. Acid , bacteriocins, H2o2
It may be that when you take this sample from the fermenter is not homogeneous, plus if the CFU is low (like Damien Bouchard had mentioned). This could explain the weird results.
Best regards.
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