Prevalence of bacteriophages infecting Staphylococcus aureus in dairy samples and their potential as biocontrol agents.

The prevalence of bacteriophages infecting Staphylococcus aureus in dairy samples was assessed. Fourteen Staph. aureus strains were used in enrichment cultures of 75 dairy samples. All samples grew specific Staph. aureus bacteriophages. According to the host range, 8 different phages were isolated. Three of them, phages PhiH5, PhiG7, and PhiA72, were found in 89% of the samples; all the isolated phages were temperate. Phages PhiH5 and PhiA72 were used in preliminary bacterial challenge tests against Staph. aureus in milk. A phage mixture (1:1) was more effective than each single phage, most likely by preventing the survival of lysogenized cells. Phages inhibited Staph. aureus in UHT and pasteurized whole-fat milk. However, the phages were less active in semi-skimmed raw milk and little inhibition was achieved in whole, raw milk. Killing of Staph. aureus was observed at room temperature and at 37 degrees C, but not at refrigeration temperature.