Antimicrobial susceptibility of oxacillin-resistant Staphylococcus spp. isolated from poultry products

Abstract

The aim of this study was to investigate the prevalence of staphylococci in raw poultry products intended for human consumption and to determine antimicrobial susceptibility, particularly of oxacillin-resistant isolates. Poultry (chicken) liver as representative samples were randomly selected in different retail markets. Isolation of staphylococci was performed using general and selective nutrient media including Mannitol Salt Agar supplemented with cefoxitin as well as Brilliance MRSA2 Agar. Antimicrobial susceptibility testing was carried out using “Sensititre” plates for determination of minimal inhibitory concentrations. Interpretation of results was performed according to CLSI standard. Polymerase chain reaction was used for determination of mec genes. Fifty samples from 70 tested were positive for Staphylococcus spp. (71%). In 30% of the isolated staphylococci, the growth was observed on selective media with cefoxitin as well as on MRSA2 Agar. The isolates from those samples were resistant to oxacillin (MIC≥0.5 mg mL-1) however, the only one isolate harboured the mecA gene. All of the isolates with phenotypic resistance to oxacillin were susceptible to vancomycin, gentamicin, linezolid, daptomicin, rifampin and quinupristin/dalfopristin. The resistances of those isolates were observed to tetracycline (60%), erythromycin (40%), and fluoroquinolones (40%). The species of oxacillin-resistant staphylococci included S. hyicus (6), S. hominis (4), S. haemolyticus (1), S. cohnii (1), S. lentus (1), S. warneri (1) and S. intermedius (1). Oxacillin-resistant Staphylococcus aureus was not found. The obtained results demonstrated low correlation between phenotypic resistance to oxacillin and the presence of mec genes in staphylococcal isolates from the poultry products. Further studies need to be performed for investigation of this unusual finding.