Phenotypic Antibiotic Resistance Pattern and Presence of mecA in Staphylococcus aureus Isolated from Bovine Mastitis

Abstract

Emergence of antibiotic resistance in Staphylococcus aureus and in particular community associated methicillin-resistant S. aureus (MRSA) is one of the most serious problem. In the present study, 97 isolates of S. aureus from cases of clinical (n=49) and subclinical (n=48) mastitis were evaluated for phenotypic antibiotic resistance patterns. A total of 28 antibiotics belonging to 10 groups of antibiotics were tested. Isolates from clinical cases of mastitis had higher resistance than those from subclinical mastitis and resistance was observed in many newly developed antibiotics as well. Multidrug resistance (MDR) was observed in 83 of the studied isolates, and of these 18 exhibited extreme drug resistance (XDR) and one isolate demonstrated resistance to all the antibiotics (pan drug resistance, PDR). Though phenotypic methicillin resistance was observed in 25 isolates, mecA was present in only 3 isolates. The antibiotic resistance is mainly attributed to acquisition of resistance genes by genetic exchange. However, the present study revealed that there may be some other mechanisms associated with methicillin resistance in S. aureus.