Sub-clinical mastitis in buffaloes: prevalance, isolation and antimicrobial resistance of Staphylococcus aureus.

This study investigated the status of clinical mastitis among milking buffaloes during the period September 2010 to August 2011 in and around Hassan district, Karnataka, India. The prevalence of mastitis was assessed by the results of bacteriological evaluation of milk samples collected from clinical and subclinical mastitis cases. The study was intended to estimate the prevalence of mastitis caused by Staphylococcus aureus (S. aureus) and the drug resistance pattern in collected milk samples. A total of 150 lactating buffalo cows were tested for mastitis employing the California Mastitis Test (CMT) and Electrical Conductivity (EC). Sixty-eight of the buffalo cows (45.33%) had mastitis, of which 29.41% (20/68) and 70.58% (48/68) showed clinical and sub clinical mastitis, respectively. A total of 68 (20 from clinical and 48 from subclinical cases) milk samples were collected and cultured for S. aureus of which 35 resulted in growth of the bacterium ( seven from clinical and 28 from subclinical cases). The Staphylococcus aureus isolates were confirmed by conventional biochemical identification. Mastitis prevalence showed significant variation at different Age (p=0.0391), Parity (p=0.0089) and Stage of Lactation lactation (p=0.0430). Thus, mastitis was more at the 4th and 7th lactations. The results of antimicrobial susceptibility testing revealed that S. aureus was highly susceptible to chloramphenicol (100%) followed by Enrofloxacin (97.14%), kanamycin (85.75%), streptomycin (82.85), Cefalexin (74.28) and gentamycin (65.71%). In contrast, isolates were highly resistant to tetracyclines (74.28%), penicillin (71.42%) and ampicillin (45.71%). In conclusion, this study confirms the importance of S. aureus as a mastitis causing bacterium and the range of antibiotics to be used in the control of mastitis.