Staphylococcus aureus in raw milk. Bacterial counts, enterotoxin production and phage-typing of the isolates

Abstract

The presence of S. aureus and its enterotoxin was investigated in 100 samples of raw milk, collected at the reception platform of a milk pasteurization plant located in Pirassununga, São Paulo, Brazil. All samples were submetted to Baird-Parker agar and positive samples were counted and tested for catalase, fermentation and oxidation of glucose, coagulase in rabbit plasma and for thermonuclease activity. A total of 201 S. aureus isolates were isolated from 50/100 (50.0%) of the samples studied, the counts varied from 30 to 110.000 bacteria per ml of milk. The enteretoxigenic capacity of the isolates was verified according to the celophane sac culture method and the detection of the enterotoxins A, B, C, D and E was by means of the double gel immunodifusion slide test, using the supernatant fluid extract obtained from the staphylococcal growths. Production of enterotoxin was demonstrated in one strain isolated from a sample that showed a count of 860 bacteria/ml and its enterotoxin belonged to type B. The enterotoxigenic strain was susceptible to the phage 53, a phage type common to human and bovine set.