Relatedness of Staphylococcus aureus strains isolated from milk and human handlers in dairy farms in Trinidad

Abstract

The susceptibility of S. aureus strains isolated from milk and human handlers in dairy farms in Trinidad to bacteriophages was determined. Of the 110 strains isolated from bulk milk, 73 (66.4%) were typable either at routine test dilution (RTD) or 100-RDT compared to 108 (72.5%) of 149 strains from composite milk sensitive but the difference was not statistically significant (P > or = 0.05; chi 2). Strains of S. aureus from human handlers had significantly (P < or = 0.05; chi 2) lower sensitivity, with only 90 (59.6%) of 151 strains typable. Phages in various groups were predominantly more active on both milk isolates, 54.1% (98 of 181) and human strains, 73.3% (66 of 90). Phage 42D alone lysed 22 (12.2%) but with other phages typed 90 (49.7%) of 181 typable strains from milk compared to a lytic activity of only 1.1% (1 of 90) alone and 35 (38.9%) with other phages for strains isolated from human handlers. The differences were however not statistically significant (P > or = 0.05; chi 2). Relatedness of S. aureus strains isolated from bulk milk, composite milk and human handlers on each farm was demonstrated in 21 (46.7%) of 45 dairy farms using the phage patterns detected. Similarly, the relatedness of S. aureus strains isolated from the anterior nares and hands of each human milker was detected on 10 (35.7%) of 28 dairy farms studied. It was concluded that S. aureus strains from human milkers contaminated both composite and bulk milk on the farms studied while bovine strains of S. aureus were also acquired by humans during milking.