Antibiotic-resistance profiles of bacterial pathogens isolated from bovine mastitis in Sanandaj, Iran

Background: Bovine clinical mastitis continues to pose a significant challenge in dairy farms, particularly due to the rise of antibiotic-resistant bacteria. This study aimed to investigate the prevalence and antimicrobial resistance profiles of key bacterial pathogens isolated from mastitic milk in Sanandaj, Iran. Methods: A total of ۲۵۰ milk samples were collected from clinically affected quarters of lactating cows in industrial dairy farms located around Sanandaj during ۲۰۲۴. Bacterial isolates were identified to the genus and species level. Antimicrobial susceptibility testing was carried out using the disc-diffusion method following CLSI guidelines, focusing on antibiotics commonly used in veterinary practice. Results: Among the ۲۵۰ milk samples, Staphylococcus aureus was the most frequently detected pathogen, present in ۱۱۰ samples (۴۴%), followed by coagulase-negative staphylococci (CNS) in ۵۵ samples (۲۲%) and Escherichia coli in ۳۵ samples (۱۴%). Other bacteria, including Streptococcus agalactiae, Klebsiella pneumoniae, and Enterococcus faecalis, were identified in ۲۰ samples (۸%). Mixed bacterial growth was observed in ۳۰ samples (۱۲%), while ۵۰ samples (۲۰%) showed no growth after repeated culture. Antimicrobial testing revealed high resistance rates to penicillin G (۷۸%), ampicillin (۷۲%), and tetracycline (۶۱%). Moderate resistance was noted for erythromycin (۴۷%) and chloramphenicol (۳۸%), whereas gentamicin (۲۴%) and trimethoprim-sulfamethoxazole (۲۸%) exhibited lower resistance. Overall, the results indicate a widespread presence of multidrug-resistant bacteria among mastitis cases in this region. Conclusion: Staphylococcus aureus emerged as the predominant mastitis pathogen in Sanandaj, showing marked resistance to penicillin and several other antibiotics. These findings underscore the importance of judicious antibiotic use and the implementation of alternative control measures in dairy farms.

کلیدواژه ها:

Bovine mastitis ، Antibiotic resistance ، Staphylococcus aureus ، Coagulase-negative staphylococci