A 23S rDNA-targeted polymerase chain reaction-based system for detection of Staphylococcus aureus in meat starter cultures and dairy products.

A polymerase chain reaction-based system for detection of Staphylococcus aureus was developed. The system consisted of the following components: (i) selective enrichment, (ii) DNA isolation, (iii) amplification of DNA with primers targeted against the 23S rRNA gene, and (iv) evaluation of the specificity of the polymerase chain reaction by Southern hybridization and nested polymerase chain reaction. The method achieved a high degree of sensitivity and unambiguity as required for the detection of contaminants in food starter preparations. The method permitted detection of Staphylococcus aureus in preparations of meat starter cultures containing Staphylococcus carnosus either alone or in combination with lactobacilli, pediococci, and/or Kocuria varians. Detection limits were sufficiently low to show within 12 h the presence of 10(0) CFU of S. aureus in starter preparations containing 10(10) CFU of S. carnosus. The system was also applied to dried skim milk and cream. For detection without selective enrichment, a protocol was developed and permitted detection of 120 CFU of S. aureus in 1 ml of cream within 6 h. With nested polymerase chain reaction, the detection limit was decreased by one order of magnitude.