Multidrug-resistant Bacterial Isolates in Bovine Subclinical Mastitis from Southern Rajasthan

Abstract

Background: In the present study two hundred milk samples were collected from cows and buffaloes with no history of clinical mastitis in the ongoing lactation, from the Sirohi district of Southern Rajasthan. Methods: The pooled sample (collected from each quarter) and examined for the status of subclinical mastitis by Modified California mastitis test and Somatic cell count respectively. Positive samples were further investigated for isolation and identification of the major mastitis-causing pathogens: S. aureus, predominant Streptococcal species and E. coli for assessing antimicrobial resistance models in southern Rajasthan. Result: The results of the current study indicate high levels of multi-drug antibiotic resistance among bacteria that commonly cause mastitis, particularly ampicillin, penicillin, tetracycline, erythromycin and methicillin. However, the highest sensitivity was conferred to ceftriaxone, gentamicin, and co-trimoxazole, suggestive of judicious use of these antibiotics in the treatment of bovine mastitis. Concurrent implementation of gradient PCR indicated the presence of mecA and blaZ genes in 51.9% and 81.4% of S. aureus isolates, respectively. Meanwhile, 56.6% of the streptococcal isolate contained the tetracycline-conferring tetM gene and none of the streptococci contained the ermB gene. The 92.3% E. coli isolates contained the tetA gene and the tetB gene for tetracycline resistance.