Isolation and antimicrobial resistance in Staphylococcus spp. associated with clinical mastitis in domestic ruminants

A study was undertaken to determine the prevalence and in vitro antimicrobial susceptibility of Staphylococcus spp. isolated from 32 mastitic milk samples received from lactating cows (12), buffaloes (9) and goats (11) of Tonk district (Rajasthan). Staphylococcus spp. was isolated (n=29) from milk samples by routine cultural technique and confirmed by 16S rRNA sequencing and NCBI blast analysis. Among the isolates, prevalence of S. aureus was maximum (41.38%) followed by S. chromogenes (20.70%), S. haemolyticus , S. gallinarum (13.79% each) and S. xylosus (10.34%). On antimicrobial sensitivity test, the Staphyloccocus spp. isolates were found resistant to ampicillin (89.6%), methicilin (79.3%), polymixin-B (82.7%), penicillin-G (79.3%), cefixime (72.4%) and enrofloxacin (55.1%). The resistance against amoxicillin-clavulanic acid, ofloxacin, norfloxacin, amoxicillin and ciprofloxacin was <50%. The study indicated that Staphylococcus spp. are the major etiologies of mastitis in domestic animals with isolates being resistant to majority of commonly used antibiotics in the treatment of mastitis. All the Staphylococcus isolates tested were susceptible to bacitracin, chloramphenicol, ceftriaxone, imipenem, doxycycline, gentamicin, chlortetracycline, tetracycline, amikacin and vancomycin and could be used in treatment of mastitis caused by Staphylococcus spp. in the region.