P1-11 Differentiation of Colony Morphology of Shiga Toxin-producing Escherichia coli on Commercial Agar Media

Monday, August 4, 2014
Exhibit Hall D (Indiana Convention Center)
Jisu Kang, University of Missouri-Columbia, Columbia, MO
Ami Yoo, University of Missouri-Columbia, Columbia, MO
Prashant Singh, University of Missouri-Columbia, Columbia, MO
Azlin Mustapha, University of Missouri-Columbia, Columbia, MO
Introduction: Shiga toxin-producing Escherichia coli (STECs) which include O157, O26, O45, O103, O111, O121, and O145 can cause serious illness in humans.  Hence, the USDA-FSIS has announced a zero-tolerance policy for these seven serotypes in raw beef productsBecause of the close relatedness among these serotypes, the ability to specifically differentiate their colonies on an agar culture medium is extremely difficult.  

Purpose: The purpose of this study was to compare among three commercial agar media, chromID® EHEC agar, EZ-CHROM STEC agar and Rainbow® agar, in their ability to effectively differentiate among colonies of these seven STEC strains.  

Methods: Pure overnight culture of each STEC serotype was streaked onto chromID® EHEC agar, EZ-CHROM STEC agar and Rainbow® agarCombinations of each strain, up to a multiple of six strains, were also streaked and colony differentiation was noted on each agar medium.  Final confirmation of each well isolated colony of each serotype was performed using serotype-specific primers and real-time PCR.

Results: EZ-CHROM STEC generated similarly colored colonies for most serotypes which were hard to differentiate and, hence, was discontinued from the study.  chromID® EHEC agar was able to clearly differentiate a cocktail of up to five serotypes, while the color differentiation obtained for the five serotype mixture was not distinguishable on Rainbow® agar.  PCR results for the colonies picked from mixed culture chromID® EHEC agar plates were in accordance with the morphological characteristics of each serotype, except for E. coli O145 and E. coli O45. 

Significance: Out of the three chromogenic media tested, chromID® EHEC agar produced the most distinctive and easily distinguishable colored STEC colonies and was the most effective for the screening and identification of the STEC serotypes in this study.