Genotypes, antibiotic resistance, and virulence factors of staphylococci from ready-to-eat food

Abstract

Sixty-seven staphylococcal isolates belonging to 12 species were obtained from 70 ready-to-eat food products. Staphylococcus aureus (n=25), and Staphylococcus epidermidis (n=13) were dominant. Susceptibility to penicillin, oxacillin, tetracycline, clindamycin, gentamicin, erythromycin, ciprofloxacin, and vancomycin was determined. All investigated S. aureus isolates were resistant to at least one antibiotic, and fifteen isolates were resistant to four and more antibiotics. Thirty-eight coagulase-negative staphylococci (CNS) isolates were resistant to at least one antibiotic, and seventeen to four and more antibiotics. Fifteen CNS isolates were mecA positive, and grew in the presence of 6 μg/mL oxacillin. All S. aureus isolates were mecA-negative. Arginine catabolic mobile element (ACME) was found in seven S. epidermidis isolates. Five S. epidermidis isolates harbored ica operon, ACME and were able to form biofilm. Three of them also possessed IS256 element and were mecA-positive. The expression of icaA gene was comparable in five ica-positive S. epidermidis isolates. One of six mecA positive S. epidermidis isolates was classified as sequence type (ST)155, one as ST110, and two as ST88. Two methicillin-resistant Staphylococcus epidermis (MRSE) belonged to new STs, that is, ST362, and ST363. Enterotoxin genes were found in 92% of S. aureus isolates. No enterotoxin gene was detected in analyzed CNS population. We show that ready-to-eat products are an important source of antibiotic-resistant CNS and potentially virulent strains of S. epidermidis, including genotypes undistinguishable from hospital-adapted clones.