Prevalence of methicillin resistance in Staphylococcus pseudintermedius isolates from dogs with skin and ear infections in South Africa

Abstract

Staphylococcus pseudintermedius is an important opportunistic commensal bacterium, often correlated with dermatitis and otitis in small animals. The emergence and rapid expansion of methicillin resistance giving rise to methicillin-resistant S. pseudintermedius (MRSP) is of concern as it is often correlated with multi-drug resistance, thereby reducing therapeutic options for these common veterinary conditions. The study aims to 1) evaluate standard laboratory methods used at five regional veterinary laboratories in South Africa to identify S. pseudintermedius; 2) determine if an association exists between resistance to first and second tier antibiotics and the presence of the mecA gene; and 3) determine if there is an association between MRSPcarriage and previous antibiotic usage. Sixty-eight presumptive MRSP clinical samples from five geographically dispersed laboratories in Republic of South Africa (RSA) were collected over a 24-month period. S. pseudintermedius was detected by a standard laboratory method and antimicrobial susceptibility testing done by means of disc diffusion. Presumptive MRSP isolates were identified when disc diffusion showed resistance to oxacillin. PCR confirmed MRSA clinical isolates by the presence of mecA. Fifty-seven samples were confirmed to harbour S. pseudintermedius (83.8%) and 49 (85%) of those were further identified to carry mecA. Of the 49 mecA positive PCR isolates, 28 were isolated from pruritic patients (28/49, 57%) and 7/49 from otitis (14%).This study provides evidence that there is a high prevalence of mecA positive carriage (85% of samples) in methicillin resistant SP pyoderma and otitis in dogs in South Africa. Important risk factors for mecA positive carriage are previous hospital admission, pruritis and previous antibacterial failure. Thus, the data suggests that there is an urgent need for better surveillance of dogs presenting with pyoderma and otitis in South Africa. Moreover, diligent antibiotic stewardship will be crucial to prevent a deterioration of this situation in the country.