Im working on a thesis with my partner about testing the amount of E.coli and Vibrio sp. present in areas in a street food vendor stall. We are collecting or samples by swabbing surfaces in the stall
Dear Antonio,
For the culturable part :
In food industry they count E.coli colonies on CHROM tbx agar (iso16649) but you also can use Mac Conkey agar or Lactose TTC.
For total Vibrio TCBS, or for pathogenic species Chrom agar or ChromID.
For the total part you can find well described qPCR method for both E.coli and Vibrio spp in the literature.
Best regards
Léa
Dear Antonio
First off, swabs are not the best way to get a bacterial count. But then again, there aren't too many options when you're sampling surfaces. I guess the best way would be be to first moisten the swabs (sterile saline would be enough), swab the surfaces using sterile swabs and wearing sterile gloves, and cutting off the swabs and putting them in test tubes containing a liquid media such as trypticase soy broth. Ensure that the swabs are in the TSB for the same duration of time (since each vendor would be at a different distance from your lab).
You could then pipette out equal volumes of the TSB using a micropipette onto the surface of MacConkey agar plates. You could count the lactose-fermenting and non-lactose-fermenting colonies before proceeding to identification.
Also, how likely is it that you would find vibrios from street food stalls? It's extremely unlikely that a food stall would have Vibrio cholerae without causing cholera outbreaks already, and other vibrios are generally found from marine sources, sewage, etc.
Best of luck for your work
Regards
Stephen
Dear Stephen,
Vibrio spp are a big component of the crustacean, bivalves, molluscs and fishes flora and these Vibrio are not necessarily pathogenic for Humans. Furthermore, pathogenic Vibrio are no longer harmful once food is cooked. It is likely to find Vibrio if they are cooking seafood.
Best Regards
Léa
Dear Léa
I do agree with you. I guess, as a clinical microbiologist, my view is often limited to only isolating pathogenic microorganisms. Vibrios could indeed be found in any setting connected to the marine environment. And what is non-pathogenic today might be observed to be pathogenic tomorrow.
Regards
Stephen
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