Pattern of antibiotic resistant mastitis in dairy cows

Abstract

To study the prevalence of drug resistant mastitis and their pattern of antibiotic resistance in dairy cows from Tamil Nadu. Materials and Methods: Isolation and identification of resistant pathogens were performed from acute clinical mastitis samples. Based on culture, isolation and sensitivity tests, cows with resistant mastitis were grouped as; Group I: Escherichia coli (n=119), Group II: Staphylococcus aureus (n=104) and Group III: Methicillin-resistant Staphylococcal aureus (MRSA) (n=12). The isolates were tested using agar disc diffusion method for their antimicrobial susceptibility and modified resazurin assay mierodilution technique for minimum inhibitory concentration (MIC) to 8 antimicrobial drugs. The organisms were also confirmed for their identity by performing PCR on the bacterial pellet targeting the specific genes such as 16s-23s rRNA, mecA and blaZ respectively for the resistant pathogens and also confirmed by sequencing. Results: Antibiotic resistant mastitis was detected in 235 out of 401 cows accounting to 56.1%. The predominant resistant causative pathogen was E. coli (50.64%) followed by S. aureus (44.25%) and MRSA (5.11%). In vitro antibiotic sensitivity test and MIC breakpoints, E. coli, S. aureus and MRSA organisms showed more sensitivity to enrofloxacin, amoxicillin + sulbactam, gentamicin and ceftriaxone and had highest resistant to penicillin followed by amoxicillin, oxytetracycline and methicillin. E. coli and S. aureus isolates were found to be resistant to 1 or 2 antimicrobials, whereas most of the MRSA isolates were found to be multi-drug resistant i.e resistance to 3 or more of antimicrobials. Out of 235 milk samples, the specific target gene 16s-23 s rRNA (E. coli), 16s-23 s rRNA (S. aureus) and MRSA (mecA and blaZ) could be amplified from 119,104and 12isolateswithapercentagepositivityof 50.64(119/235), 89.64(104/116)and 10.34(12/116)respectively. Conclusion: Prevalence of antimicrobial resistance (AMR) in bovine mastitis pathogens was high. Most MRSA pathogens were multidrug resistant. E. coli and S. aureus isolates were resistant to few antimicrobials. © The authors.