Detection of Escherichia coli O157:H7 and Listeria monocytogenes in beef products by real-time polymerase chain reaction

Foodborne Pathog Dis. 2004 Winter;1(4):231-40. doi: 10.1089/fpd.2004.1.231.

Abstract

Rapid methods for the detection of Escherichia coli O157:H7 and Listeria monocytogenes in food products are important to the food industry and for public health. Conventional microbiological methods and newly developed molecular-based techniques such as polymerase chain reaction (PCR)-based methods are time consuming. In this study, a faster method based on utilization of a hybridization probe with real-time PCR, was developed and applied for detection of E. coli O157:H7 and L. monocytogenes from artificially contaminated raw ground beef and fully cooked beef hotdogs. Target genes for E. coli O157:H7 and L. monocytogenes were rfbE and hylA, respectively. An analysis of 169 bacterial strains showed that the chosen primers and probes were specific for detection of E. coli O157:H7 and L. monocytogenes by real-time PCR. The assay was positive for nine of 10. E. coli O157:H7 strains, and all L. monocytogenes (7/7) strains evaluated. Bacterial strains lacking these genes were not detected by these assays. Detection limits of real-time PCR assays ranged from 10(3) to 10(8) colony forming units (CFU)/ml for E. coli O157:H7 in modified tryptic soy broth and 10(4) to 10(8) CFU/mL for L. monocytogenes in Fraser Broth. Detection sensitivity ranged from 10(3) to 10(4) CFU/g of raw ground beef or hotdog without enrichment for E. coli and L. monocytogenes. Approximately 1.4-2.2 CFU/g of E. coli O157:H7 in raw ground beef were detected following an enrichment step of 4 h. Approximately 1.2-6.0 CFU/g of L. monocytogenes in beef hotdogs were detected following an enrichment step of 30 h. The real-time PCR assays for detection of E. coli O157:H7 and L. monocytogenes in raw ground beef and beef hotdogs were specific, sensitive and rapid.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cattle
  • Colony Count, Microbial
  • Consumer Product Safety*
  • DNA, Bacterial / analysis
  • Escherichia coli O157 / isolation & purification*
  • Food Contamination / analysis
  • Food Microbiology
  • Listeria monocytogenes / isolation & purification*
  • Meat Products / microbiology*
  • Polymerase Chain Reaction / methods*
  • Sensitivity and Specificity
  • Time Factors

Substances

  • DNA, Bacterial