Resistance to methicillin of coagulase-negative staphylococci (CNS) isolated from bovine mastitis

The aim of this study was to determine the mechanisms of staphylococcal resistance to methicillin. CNS (n=100 isolates) were prepared from the mammary inflammatory secretions of 86 cows from farms located in the Lublin region. Methicillin-resistant isolates constituted 20.0% of all CNS. Staphylococcus sciuri (n=8) and Staphylococcus xylosus (n=6) were most abundant, followed by Staphylococcus chromogenes (n=3), Staphylococcus haemolyticus (n=2) and Staphylococcus warneri (n=1). The mecA gene was found in 50.0% of MRCNS (10.0% of all CNS isolates) belonging to two species: S. sciuri and S. xylosus. All mecA-positive isolates contained the protein of low affinity to penicillin (penicillin-binding protein 2a – PBP2a). The enzyme hydrolysing the β-lactam ring in antibiotics was detected in 40.0% of MRCNS; 10.0% of MRCNS isolates were characterised by the presence of the mecA gene and ability to produce β-lactamase. The remaining 20.0% of MRCNS isolates showing phenotypic resistance to methicillin were mecA gene-negative and were not able to produce β-lactamase.