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

J Food Prot. 2002 May;65(5):752-9. doi: 10.4315/0362-028x-65.5.752.

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 degrees 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-beta-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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cattle
  • Cattle Diseases / epidemiology*
  • DNA, Bacterial / analysis*
  • Dairying
  • Electrophoresis, Gel, Pulsed-Field
  • Escherichia coli Infections / epidemiology
  • Escherichia coli Infections / veterinary*
  • Escherichia coli O157 / genetics
  • Escherichia coli O157 / isolation & purification*
  • Escherichia coli O157 / pathogenicity
  • Feces / microbiology*
  • Female
  • Milk / microbiology*
  • Phylogeny
  • Polymerase Chain Reaction / veterinary
  • Prevalence
  • Tennessee / epidemiology
  • Virulence

Substances

  • DNA, Bacterial