Clonal diversity and biofilm-forming ability of methicillin-resistant Staphylococcus pseudintermedius.

Objectives: The aim of this study was to investigate the clonal epidemiology of methicillin-resistant Staphylococcus pseudintermedius (MRSP) isolates from dogs in Norway and to evaluate the antimicrobial resistance patterns and determine the biofilm-forming abilities of the isolates.

Methods: All MRSP index isolates from each MRSP-positive dog detected in Norway until June 2011 were included (n = 23). The MICs of antimicrobial agents were determined by the VetMIC™ microdilution method. The genetic relationship between the isolates was investigated by multilocus sequence typing (MLST) and PFGE. The isolates' abilities to form biofilm on polystyrene were studied.

Results: The MRSP isolates investigated grouped into 11 different sequence types (STs); MRSP ST106 occurred most frequently. There were a relatively smaller number of isolates belonging to ST71, the largely predominant ST in Europe. Isolates belonging to ST71 had a significantly greater ability to produce biofilm compared with the other isolates, and especially compared with MRSP ST106.

Conclusions: A heterogeneous clonal distribution was observed among MRSP from dogs in Norway. As opposed to previous findings in Europe, MRSP clones other than ST71 have spread in Norway, such as MRSP ST106. The results also show that MRSP ST71 is possibly a good biofilm producer, and this may in turn be a contributing factor to the nosocomial character of MRSP ST71.