Prevalence and Molecular Characterization of Escherichia coli O157:H7 in Bulk Tank Milk and Fecal Samples from Cull Cows: A 12-Month Survey of Dairy Farms in East Tennessee
Abstract:A study on the prevalence of Escherichia coli O157:H7 was conducted on 30 dairy farms in east Tennessee between May 2000 and April 2001. This pathogen was isolated from 8 of 30 (26.7%) dairy farms at various sampling times. A total of 415 fecal samples from cull dairy cows and 268 bulk tank milk samples were analyzed. Overall, 10 of 683 (1.46%) samples (2 of 268 [0.75%] milk samples and 8 of 415 [1.93%] fecal samples) tested positive for E. coli O157:H7. Food and Drug Administration Bacteriological Analytical Manual protocols were used for the conventional isolation and confirmation of E. coli O157:H7. Samples were shake cultured (150 rpm) at 42°C for 24 h in tryptic soy broth containing 2 mg of novobiocin per liter. White colonies isolated on cefixime-tellurite sorbitol MacConkey agar plates were evaluated for fluorescence on sorbitol MacConkey agar supplemented with 0.025 g of methylumbelliferyl-β-D-glucuronide per liter. Nonfluorescing white colonies were biochemically typed and serologically confirmed. Multiplex polymerase chain reaction profiles of E. coli O157: H7 isolates indicated the presence of common virulence factors (Shiga toxin, enterohemolysin, and intimin) of Shiga toxin–producing E. coli, suggesting the potential human pathogenicity of bacterial isolates. Pulsed-field gel electrophoresis profiles of SpeI and XbaI restriction enzyme–digested genomic DNA were used to establish relatedness among bacterial isolates. Data from this study indicate that both cull dairy cows and bulk tank milk pose a potential hazard with regard to human foodborne illness. It is therefore imperative to develop on-farm and preharvest pathogen reduction programs to control the carriage of E. coli O157:H7 pathogens.
Document Type: Research Article
Affiliations: University of Tennessee Food Safety Center of Excellence, Knoxville, Tennessee 37996, USA
Publication date: May 1, 2002
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