Molecular characterisation of antimicrobial resistance in coagulase negative staphylococci isolated from bovine subclinical mastitis

Abstract

Coagulase negative staphylococci (CNS) are emerging as the most prevalent causative agent of bovine mastitis. They are resistant to many commonly used antibiotics due to the presence of antimicrobial resistance (AMR) genes. A study was conducted to evaluate the AMR profiling of CNS isolated from bovine subclinical mastitis.Coagulase negative staphylococci were isolated from 49 (44.95 per cent) of the subclinical mastitis samples. Disc diffusion assay revealed that highest resistance was shown against gentamicin (42.85 per cent) followed by methicillin (32.6 per cent), ceftriaxone – tazobactam (24.48 per cent), enrofloxacin (20.4 per cent), tetracycline (16.32 per cent) and least resistance to cotrimoxazole (4 per cent). Genotypic characterisation of AMR genes such as mecA, aacA-aphD and norA by PCR was done for determining resistance to methicillin, gentamicin and fluroquinolone resistance. The CNS carried aacA-aphD, norA and mecA in 44.89 per cent, 32.65 per cent and 14.28 per cent, respectively. Comparison of phenotypic and genotypic characterisation of AMR in CNS was carried out by McNemar test and it was found that there was significant difference between the presence of mecA gene and methicillin resistance. There was no significant difference noticed forcharacterisation of phenotypic and genotypic AMR of CNS for gentamicin and fluroquinolone resistance.