Suppose I am using MacConkey broth for E. coli testing (MPN method) and after completion of test, observed results are negative for the presence of E. coli.
Now the colour of medium will remain unchanged even after few days, so can we use this media for testing of E. coli of another sample .
Can we do this with any other media?
If you use for a very specific application like gene expression after you grow bacteria or preparation stock for -70C etc. it is not suggested to use already used media broth. But if you just grow several strain to see antimicrobial effect or test antibiotic concentration etc. for selection, you may use it.
Instead of re-using the same media; I suggest that just try to use 96 well plate to reduce amount of usage of broth.
Good luck
Ali
good suggestion by Ali
Instead of re-using the same media; I suggest that just try to use 96 well plate to reduce amount of usage of broth.
Microbial culture media can not be generally used for microbiological tests more than once.
In this case, because:
The positive result in MacConkey broth for E. coli testing (MPN method) is acid+gas from lactose sugar fermentation.
The negative tubes from the first use do not contain positive lactose fermenting microbial types, but may be, they contain other microbial types cells (negative lactose fermentation), which when be used again, get contain two microbial types, both of them are negative lactose fermentation, but they have synergistic effect:
Which means, one of microbial type make metabolism of the culture medium ingredients and give new compounds (its metabolic products, not acid+gas), then another microbial type uses the metabolic products of the first microbial type and give acid+gas (but really it is false positive result).
So, for microbiological tests of samples, positive tubes have to be followed by recommendation tests (minimum Gram stained slide) to be sure that. positive result gets from the intended microbial type.
Not recommended reuse of microbiological media. Instead, use ready prepared kits to minimize use of agar/broth.
Also, one sterilized media plate can be used for testing 4-5 bacteria, only if their colonies does not spread.
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