Detection of tet(M) gene from raw milk by rapid DNA extraction followed by a two-step PCR with nested primers

J Food Prot. 2004 Dec;67(12):2833-8. doi: 10.4315/0362-028x-67.12.2833.

Abstract

The likelihood that milk and milk products may act as a vehicle for antibiotic-resistant bacterial genes has become a concern to the food industry and a public health issue, and the demand for rapid tests has increased. The purity of DNA extracted from food samples is a key issue in the sensitivity and usefulness of biological analyses, such as PCR for pathogens and nonpathogens. A rapid, phenol-chloroform free method based on a modification of a sodium iodide DNA extraction, followed by a two-step PCR was developed for direct detection of the tet(M) gene in milk samples within a single working day. This study compares the proposed method with a traditional phenol solvent extraction method and with a commercial kit (QIAamp DNA blood mini kit, Qiagen). The three DNA extraction methods were used to ensure access to the tet(M) gene from 1 ml of raw milk, inoculated with a strain of Enterococcus faecalis, which carries the tet(M) gene. The proposed method, followed by a two-step PCR with nested primers specific for the tet(M) gene, was able to reach a detection limit below 10 CFU/ml in less than 4 h, including the two amplification cycles, thus outperforming in sensitivity and rapidity both the traditional and the commercial method.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • DNA, Bacterial / isolation & purification*
  • Enterococcus faecalis / genetics*
  • Food Contamination
  • Gene Amplification
  • Milk / microbiology*
  • Polymerase Chain Reaction / methods*
  • Sensitivity and Specificity

Substances

  • DNA, Bacterial