[Microbiology] Re: USP Microbial Limits Prep Test (Christina Benson)

Kate Hawley via microbio%40net.bio.net (by labcat76 from yahoo.com)
Wed Sep 9 18:42:53 EST 2009

Christina:In testing antimicrobials, neutralization should always be carried out to define the testing period.  For example, you are looking at bleach and wonder how many bacteria are killed in a 15 second contact period.  You expose the bacteria to the bleach for 15 seconds, then recover them in neutralizer.  This stops the action of the bleach, the test period is defined as 15 seconds.  Then plate the solution and wait for the 24 to 48 hours to see how many organisms survived and calculated your reduction from the inoculum (or zero time) organism count.  If you had recovered the organisms in phosphate buffer or water, the bleach would still be acting on the organisms over the period required to enumerate the bacteria and your test period now is undefined or at best the whole 24 to 48 hours it takes to look at the plates.  Regardless of the antimicrobial, whether fast acting like bleach/disinfectants or slower like silver or triclosan,
 neutralization is required for understanding kill times.  Common neutralizers include letheen broth, D/E broth, and SCDLP, but you need to determine the appropriate neutralizer for your antimicrobial.

Katherine Harrell Hawley 

Message: 1
Date: Tue, 8 Sep 2009 16:52:12 -0600
From: "Christina Benson" <cbenson from nutritionallabs.com>
Subject: [Microbiology] USP Microbial Limits Prep Test
To: <microbio from magpie.bio.indiana.edu>
Message-ID: <24031E4AE32244F98F946FA60DED23FC from NLNT>
Content-Type: text/plain;    charset="us-ascii"

Hi there,

I was wondering if you would be willing to share the SOP you wrote on how to
perform the prep test?  I am having a hard time figuring it out.  I also
think it is kind of an oxymoron to be testing antimicrobial stuff.
Antimicrobial is good, right?  Why ruin it by neutralizing?

Thanks for your time,

Christina Benson


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