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Beef processors have a need for quick, easily administered, accurate and cost-effective tests for
detection of E. coli O157:H7. Historically, enumeration of various bacterial populations (total
aerobic bacteria, Enterobacteriaceae, generic E. coli, etc.) has been used to give an indication of
trends in pathogen population. These methods show the presence of the pathogen but do not
estimate total numbers. Conversely, tests evaluating pathogen populations directly, especially E.
coli O157:H7, are more costly, labor intensive and take multiple days to generate results. <P>
There are a variety of methods to identify members of diverse bacterial populations.
Biochemical assay-based methods have traditionally been used to classify individual strains.
These methods are slow and the results are biased towards those strains that are amenable to
cultivation in the lab. <P>
Molecular-based methods are now being used more frequently and they don't require culturing
of the organism prior to identification. One such method is denaturing gradient gel
electrophoresis (DGGE). DGGE classifies organisms based on the melting profile from
amplified segments of target genes. For the purposes of this study, the 16S ribosomal RNA gene
served as the target gene. The genus and species of several bacteria can be derived based on the
unique sequence of the 16S rRNA gene. The constituents of the microbial populations will be
determined without enrichment, thus reducing bias towards those strains amenable to in vitro
culture. <P>
The objective of this study was to determine if a bacterial strain from the bovine-associated
bacterial population cans serve as an indicator organism E. coli O157:H7.
Findings: Bovine fecal and pre-evisceration carcass samples were collected and analyzed for the presence of E. coli O157:H7. Concurrently, the microbial DNA from each sample was extracted and portions of the 16S rRNA genes were amplified and separated using denaturing gradient gel electrophoresis (DGGE). The banding patterns were analyzed. No bacterial species could be identified that either positively or negatively correlated with the presence of E. coli O157:H7.