Molecular characterization of methicillin-resistant Staphylococcus aureus strains from pet animals and their relationship to human isolates

Objectives: Methicillin-resistant Staphylococcus aureus (MRSA) isolates from pet animals were characterized and compared with human isolates from clonal complexes most prevalent in Central Europe. Methods: S. aureus isolates were investigated for their in vitro susceptibility to antimicrobial agents by broth microdilution. Resistance genes and the Panton-Valentine leucocidin gene lukF-lukS were identified by PCR. All isolates were characterized by SmaI macrorestriction analysis and spa typing to assess their genomic relationships. Representative isolates were additionally analysed by multilocus sequence typing and PCR-directed SCCmec typing. Results: All pet isolates carried the resistance genes mecA and erm(C) and proved to be resistant to beta-lactams and MLSB antibiotics. In addition, all isolates were resistant to fluoroquinolones. None of the pet isolates carried the Panton-Valentine leucocidin gene lukF-lukS. Macrorestriction analysis revealed that the pet MRSA isolates exhibited four closely related SmaI fragment patterns. Moreover, all isolates revealed spa type t032. Further analysis of representatives of the different PFGE types revealed the presence of multilocus sequence type ST22 in combination with a type IV SCCmec element. Thus, molecular typing results were similar for pet strains and human ST22 reference strains. Conclusions: Based on their strain characteristics, the MRSA isolates from pets investigated in this study closely resembled ST22 MRSA isolates which are widely disseminated in German hospitals. The results of this study indicate that cross-transmission of MRSA between pet animals and humans might have occurred.