Prevalence and Antibiotics Resistance Patterns of Common Bacterial Causes of Bovine Subclinical mastitis in Selected Dairy Farms of Gorgan, North-east of Iran

The aim of this study was to determine the prevalence of bovine mastitis, isolate of mastitis-causing bacteria and characterize antimicrobial resistance pattern at selected dairy farms around Gorgan, Golestan province. Among 60 lactating cows, 16 (26.6%) cows were positive bovine for subclinical mastitis by California Mastitis Test. Bacterial culture and Agar disc diffusion was used for isolation and antibiotic susceptibility test. The most prevalent isolated bacteria were Staphylococcus aureus (36 cases, 45% (and coagulase-negative Staphylococci (18 cases, 22.5 %,( followed by Eschershia coli (14 cases, 17.5%), Klebsiella pneumonia, Pseudomonas aeruoginosa and Streptococci (4 each, 5%). Antimicrobial susceptibility testing revealed that 92.5% and 82.5% of total isolates were susceptible to gentamycin and ciprofloxacin, respectively. In addition, the E. coli isolates showed 92.8% sensitivity to neomycin. However, the highest resistance was observed against penicillin (90%), trimethoprim/sulfamethoxazole (87.5%) and erythromycin (82.5%). Based on the results, gentamycin and ciprofloxacin may be considered the drugs of choice for mastitis treatment whereas penicillin, trimethoprim-sulfamethoxazole and erythromycin were found to be poor in their efficacy to the isolates. In this study, 62.5% of the isolates (50 isolates) were multiple-drug resistance. Based on the results, it seems that gentamicin and ciprofloxacin are more appropriate drugs for the treatment of mastitis. However, to minimize the risk of resistant bacteria, it is necessary to perform antibiogram testing prior to antibiotic prescription and evaluate the antibiotic resistance pattern periodically in each geographical area.