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weird bacteria

JEDilworth bactitech at nospamhortonsbay.com
Mon Mar 3 21:02:57 EST 2003

However, one colony of Proteus mirabilis (or P. vulgaris) can eventually 
swarm over an entire plate. Getting bacteria subcultured and away from 
Proteus sp. is a constant problem with mixed cultures of pathogens that 
include it. This is why most clinical specimens are also plated on 
MacConkey agar, which inhibits Proteus's swarming proclivities for the 
most part. MacConkey, however, only grows gram negative rods. To split a 
gram positive away from a Proteus one must subculture onto a CNA or 
other plate that includes antibiotics. CNA stands for Colistin/Naladixic 
Acid, so anything that is sensitive to this will not grow on CNA. It 
inhibits most gram negatives with the exception of very resistant ones.

I looked at the picture of the colony and it looks like you've picked up 
a swarmer that's growing all over everything. Without using some sort of 
selective medium, you're kind of stuck as to splitting the organisms.

Judy Dilworth, M.T. (ASCP)
Microbiology (Clinical, 29 years)

> No, Proteus mirabilis, for example, grows as a discrete colony onstead of
> swarming.
> Annie ;o)

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