coa types and antimicrobial resistance profile of Staphylococcus aureus isolates from cases of bovine mastitis

The objective of the study was to determine the interrelationship between coa types of Staphylococcus aureus isolates from bovine mastitis cases and their susceptibility patterns to commonly used antimicrobial agents. In this study, a total of 63 S. aureus isolates obtained from 387 clinical and subclinical bovine mastitis milk specimens were examined for antimicrobial susceptibility against various classes of antibiotics and coa typing according to the size of the PCR product. Overall, five resistance profiles, nomenclatured PA, PAAc, PAE, PAAcE, and PAAcT according to their resistance and five different coa types, numbered I to V, were noted among the isolates studied. The most coa types were type I (38.1% of the 63 isolates) and type III (36.51%) and indicates that a few coagulase gene types of S. aureus are responsible for the majority of bovine mastitis cases. Resistance to penicillin, ampicillin, and amoxicillin/clavulanic acid were most common, respectively, with 63 (100%), 63 (100%), and 41 (65.1%) isolates and appeared to be higher than those usually reported. No resistance was detected for trimethoprim and gentamicin. Furthermore, a good relationship between phenotypic antibiogram and the polymorphism of coagulase gene was found in this study. Predominant coa types I and III were significantly associated with resistance profiles PAAcT and PAAcE, respectively. These two predominant types also showed high antibiotic resistance characteristic in comparison with rare types. As a result, this study illustrated a tendency for isolates from different coa types to have specific antimicrobic susceptibility profiles, presumably because of genetic diversity between isolates and/or selection force through the use of drugs.