Background and Aim: Bovine mastitis has long been considered the most important cause of economic losses in the dairy industry. Staphylococcus aureus is the most frequently isolated pathogen from bovine mastitis cases worldwide. Capsular polysaccharides (CPs) of serotype 5 (CP5) or serotype 8 (CP8) are the most prevalent capsule genotypes related to infections associated with S. aureus in humans. However, a variety of CPs has been reported in ruminants and other hosts. Information regarding the relationship between genotypic and phenotypic capsule variation and bovine mastitis in Jordan is scarce. Thus, we aimed to determine the prevalence of S. aureus capsule genotypes CP5 and CP8 in milk from bovine mastitis cases and the antimicrobial susceptibility profile of the recovered isolates in 27 dairy farms in Jordan.

Materials and Methods: Staphylococcus aureus strains were isolated from bovine mastitis cases in two districts of Jordan. All S. aureus isolates were initially identified using conventional biochemical and microbiological methods. Subsequently, confirmation of the identity of S. aureus was performed by polymerase chain reaction (PCR) targeting nuc gene. Capsule polysaccharide typing was performed by PCR specific for CP5 and CP8. In addition, we assessed the antibiotic susceptibility profile of S. aureus isolates against commonly used antimicrobials by the disk diffusion method according to Clinical and Laboratory Standards Institute guidelines.

Results: We collected 148 clinical isolates of S. aureus from bovine mastitis cases in the Zarqa (67.6%, n = 100) and Irbid (32.4%, n = 48) districts. Most isolates possessed capsule genotypes (91.3%), predominantly CP8 (88.6%). Only 8.7% of the isolates were nontypeable by PCR. In addition, we found statistically significant differences between the geographical region and the status of methicillin-resistant capsule genotypes (p < 0.05). The rates of resistance to β-lactam, macrolide, and fluoroquinolone antibiotics were very low, but resistance to tetracyclines was considerably high (22.3%). Significantly, mastitis isolates from Irbid showed a higher rate of resistance to ciprofloxacin (8.3% vs. 0%), while isolates from Zarqa showed a significantly higher rate of resistance to gentamicin (12.0% vs. 6.2%).

Conclusion: We established associations between capsule genotypes and antimicrobial resistance and the pathogenic behavior of S. aureus isolated from bovine mastitis cases. Further studies are necessary to fully elucidate the role and mechanisms of capsular expression in the epidemiological and molecular variability of S. aureus in bovine mastitis.

Keywords: antibiotic susceptibility, bovine mastitis, capsule genotypes, polymerase chain reaction, Staphylococcus aureus.