Characteristics of drug-resistant staphylococci isolated from milk of lambed ewes during the perinatal period.

Introduction: Staphylococci are still a challenge in veterinary medicine, as they are one of the aetiological factors causing clinical and subclinical mastitis in small ruminants. The aim of the study was to analyse the occurrence of staphylococci in milk obtained from Świniarka (SW) and Uhruska (UHR) sheep and to characterise their drug resistance and virulence.

Material and methods: In total, 50 milk samples were collected from ewes seven days after parturition. Drug susceptibility analysis was performed based on Clinical and Laboratory Standards Institute standards and demonstration of the presence of resistance genes was attempted.

Results: Staphylococcus spp. strains were identified in 70% of the samples, and 57.2% of the strains were S. aureus. Most of the tested strains (88.6%) were resistant to at least one antimicrobial, and resistance to tetracycline and erythromycin was the dominant type in S. aureus strains. Coagulase-negative species (CoNS) exhibited resistance predominantly to penicillin, cefoxitin and tetracycline (86.6%, 73.3% and 46.6%, respectively).The presence of the mecC gene was detected in four cefoxitin resistant strains. In tetracycline- and chloramphenicol-resistant strains, phenotypic and genotypic resistance was statistically significantly more common among strains isolated from UHR than SW.

Conclusion: The present study highlights the problem of potential subclinical mastitis caused by drug-resistant strains of S. aureus and other CoNS species in lambed ewes. However, the occurrence of virulence factors in these strains is very rare.