[Microbiology] Re: observing and counting bacteria within soft agar

John Gentile via microbio%40net.bio.net (by yjgent from nospamcox.net)
Mon Dec 7 20:08:36 EST 2009

On 2009-12-07 14:05:19 -0500, Pavitra <pavitra.padmanabhan from gmail.com> said:

> Hi,
> Is there a simple way to count bacteria that are growing as a lawn in  
> soft (top) agar? I'm working with E.coli. Would gram staining work?
> Thanks.

Your question shows that you don't quite understand the basics of 
microbiology cultures. There are many methods of counting bacteria, 
some of which are counting colonies on agar, others require developing 
a growth curve with a spectrophotometer.

You need to go back to your basic micro book and look up the topic of 
colony counts. Learn how to make serial dilutions in a broth that will 
support your bacteria and then how to plate a small enough aliquot to 
give you countable colonies. Then you can calculate your bacterial 
count per ml or what ever you are trying to count.

By the way, a "lawn" of growth refers to a confluent growth across the 
whole plate, and not countable discrete colonies.
John Gentile MS, M(ASCP)
Laboratory Information Mgr.
VA Medical Center
Providence, RI 
yjgent from cox.net

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