[Microbiology] Re: issues with suspected E. coli

John Gentile via microbio%40net.bio.net (by yjgent from nospamcox.net)
Thu Apr 10 21:23:23 EST 2008

On 2008-04-09 16:10:17 -0400, "Nathan Tisdell" <amurion from gmail.com> said:

> I am currently taking an introduction to microbiology class and am having
> issues with a strain of bacteria.  We have run SIM tests, Citrate, MR-VP,
> TSI and EMB tests.  Every test points to it being E. Coli except for the EMB
> plate, instead of turning purple with a green sheen, it stayed colorless.  I
> did not streak for isolation, just a straight streak across the medium.  If
> someone could let me know about something that I might be missing, I would
> greatly appreciate it.

The first thing I teach to anyone in micro is that the bacteria don't 
read the book. You were probably told that E. coli is lactose postive, 
indole positive, H2S negative, etc. It all fits in with your nice 
charts and it looks easy.

I have seen too many variations of E. coli including one that was H2S 
positive - it almost looked like a Salmonella. Look for other tests 
that ONLY E. coli will be positive for. An obsolete test I liked ( and 
was a bit dangerous) was growth in NaCn broth, which I had to make 
fresh, and I mouth pipetted the Na cyanide!

Look at the charts some more, you are bound to find something.
John Gentile MS, M(ASCP)
Laboratory Information Mgr.
VA Medical Center
Providence, RI 
yjgent from cox.net

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