Polymerase Chain Reaction Identification of Enteroinvasive Escherichia coli Seeded into Raw Milk

Molecular biological techniques for identifying pathogenic foodborne bacteria use small amounts of bacterial nucleic acids that must be purified and concentrated from complex food matrices. The polymerase chain reaction (PCR) amplifies specific segments of DNA and speeds the identification of bacterial strains. Methods for preparing DNA for PCR analysis were tested by seeding enteroinvasive Escherichia coli (EIEC) cells into raw milk. Test samples of milk were heated at 35°C and were treated with proteinase and detergent. As few as 10² cells of EIEC per ml of seeded milk were identified after amplification of a plasmid-borne gene required for invasion.