Methicillin-resistant Staphylococcus pseudintermedius (MRSP) from healthy dogs in Norway - occurrence, genotypes and comparison to clinical MRSP.

The aim of the study was to investigate the occurrence of methicillin-resistant Staphylococcus pseudintermedius (MRSP) in healthy dogs and further to determine genetic relatedness between carrier isolates and clinical MRSP from dogs in Norway. A total of 189 healthy dogs visiting ten veterinary clinics were screened for MRSP during the period February to April 2013. Carrier isolates were susceptibility tested with disk diffusion and genotyped using multilocus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE). Forty-nine clinical MRSP were characterized for comparison. These isolates were collected from July 2008 to April 2013 and represent all MRSP index isolates from each MRSP-positive dog detected in Norway until April 2013. Geographical distribution of all MRSP cases was investigated using the ArcGIS 9.3 Software. MRSP was detected from five (2.6%) healthy dogs, sampled at three different clinics. The isolates grouped into three sequence types (STs): ST252 (two isolates), ST71 (two isolates) and ST306 (one isolate). MRSP from dogs sampled at the same animal clinic belonged to the same ST and produced identical PFGE pattern. The 49 clinical MRSP grouped into 15 STs; ST258 (n = 17), ST71 (n = 10), and ST305 (n = 4) were the most prevalent. The MRSP carrier isolates were genetically related to MRSP variants from dogs with infections as ST306 (from a carrier) is related to ST258. MRSP ST252, found in two carriers, was also present among the clinical MRSP isolates. Altogether the MRSP isolates were genetically diverse and MRSP of other lineages than ST71 continues to disseminate in Norway. Susceptibility testing showed that MRSP isolates of the ST71 lineage were the most multiresistant. Our study showed that MRSP could be detected in healthy dogs without infections and with no recent history of antimicrobial therapy stressing the need for future monitoring, infection control and prudent use of antimicrobial agents.