Prevalence and characteristics of Staphylococcus aureus strains isolated from bulk and composite milk cattle handlers

ABSTRACT

The prevalence and characteristics of Staphylococcus aureus strains isolated from bulk and composite milk and from cattle handlers on dairy farm all 175 bulk milk samples tested (100 percent) while 280 of 287 composite milk samples (97.6 percent) yielded S. aureus. The mean counts of S. aureus in bulk milk ranged from 5.9 x 10(3) to 1.2 x 10(5) CFU/ml compared with mean S. aureus counts in composite mild which ranged from 2.4 x 10(3) to 3.0 x 10(4) CFU/ml. Of the 105 strains of S. aureus from bulk milk tested, 45 (42.9 percent) were enterotoxigenic elaborating staphylococcal enterotoxin A (SEA), SEB, SEC, SED, or a combination compared to 69 of 146 stains (47.3 percent) recovered from composite milk which were enterotoxigenic, but the difference was not statistically significant (P > 0.05; chi 2). Twenty-two of 42 bulk milk samples containing enterotoxigenic S. aureus (52.4 percent) had counts of the organism which exceeded 10(4) CFU/ml. For S. aureus strains isolated from cattle handlers, 66 of 146 (45.2 percent) were enterotoxigenic. Prevalence of resistance to nine antimicrobial agents tested was 18.7 percent and 12.9 percent among bulk milk and composite milk isolates, respectively, compared to 49.3 percent and 69.5 percent among isolates from human anterior nares and hand swabs, respectively. Resistance to ampicillin and penicillin was highest among both milk (12.2 percent) and human (53.6 percent) isolates of S. aureus, and the difference was stastically significant (P < or in 0.001; chi 2). It was concluded that bulk milk containing relatively high counts of enterotoxigenic S. aureus may constitute a health hazard to consumers(AU)