Antimicrobial resistance and genotypes of staphylococci from bovine milk and the cowshed environment

Abstract

Investigation of antimicrobial resistance and genetic relatedness of staphylococci from milk of cows with mastitis and cowshed environment was the aim of this study. Antimicrobial resistance against 14 antimicrobials were determined by using a disc diffusion method. Genetic similarity between the most frequently isolated species was analysed by PFGE (pulsed-field gel electrophoresis). Haemolytic activity, DNase, protease and esterase production was also investigated. Coagulase-negative Staphylococcus species were isolated from 30.8% of milk samples from cows with mastitis. The most frequently isolated species was Staphylococcus xylosus and yield of these organisms was significantly associated with milk of mastitis cows. S. epidermidis was a predominant penicillin-resistant species. High frequency of resistance to lincomycin was observed among isolates of S. sciuri (54.2%) and S. xylosus (25.9%) from cows with mastitis. PFGE (pulsed-field gel electrophoresis) analysis of 29 Staphylococcus aureus isolates showed the presence of 17 PFGE pulsotypes. Isolates of S. sciuri (n = 36) had unique PFGE patterns. Some S. xylosus isolates from milk and milker's hands had the same PFGE pulsotypes, and this observation could indicate that dairyman may be a potential source of the infection. The pulsotype of each of the remaining isolates of S. xylosus suggested that they might have come from common environmental sources; however, these isolates differed in antibiotic resistance pattern or virulence traits. Therefore, knowledge about antibiotic sensitivity pattern and virulence factors of a CNS isolate, besides its genotype, may be informative in tracking the source of the infection.