Investigation into antimicrobial resistance, enterotoxin and cassette chromosome gene of Staphylococcus aureus isolates from humans, cows and goats in Taiwan

Multidrug-resistant Staphylococcus aureus (MDR S. aureus) is predominately present in humans and animals. Staphylococcal enterotoxin (SE) is one of the representative toxins produced by S. aureus. The drug resistance patterns, presence of eighteen SE genes and staphylococcal cassette chromosome (SCCmec) in S. aureus strains isolated from human cellulitis, septicemia, mastitis and farmed ruminant mastitis were investigated and analyzed. Methicillinresistant S. aureus (MRSA) and methicillin-sensitive S. aureus (MSSA) accounted for 51.35% (76/148) and 48.65% (72/148), respectively. Both MSSA and MRSA carried sea (15%), seb (30.8%) and sek (27.5%) genes. Eighty percent of the MRSA strains (52/65) belonged to SCCmec types I, III and IV while the MSSA strains were mostly untypable. Molecular examination of SE genes showed that sec might be highly crucial for goat S. aureus mastitis while sel might play a role in human, goat and cow mastitis. Enterotoxin A gene displayed the highest rate of appearance in the isolates from cow S. aureus mastitis as the enterotoxin was also found in human cellulitis, septicemia and mastitis, showing its key role in bovine mastitis and cross-species implications between humans and cows. MDR S. aureus widely appeared in human hospitals and community, and goat mastitis, whereas the strains accounted for much lower prevalence in cow mastitis. The data indicate that the patterns of SE gene are probably host species-specific and source-associated; therefore, the identification of SE genes coupled with SCCmec typing might be a useful method to trace the sources of infection in farmed ruminants and humans.