Clonal Diversity, Virulence Patterns and Antimicrobial and Biocide Susceptibility Among Human, Animal and Environmental MRSA in Portugal

Objectives: The objective of this study was to identify the Staphylococcus aureus clonal types currently circulating in animals, humans in contact with animals and the environment in Portugal based on genetic relatedness, virulence potential and antimicrobial/biocide susceptibility.

Methods: Seventy-four S. aureus isolates from pets, livestock, the environment and humans in contact with animals were characterized by SCCmec typing, spa typing, PFGE and CC398-specific PCR, by antimicrobial and biocide susceptibility testing and by detection of resistance genes and genes for efflux pumps. Representative strains were analysed by DNA microarray and MLST.

Results: The S. aureus isolates represented 13 spa types and 3 SCCmec types and belonged to three clonal complexes (CC5, CC22 and CC398). Most of the isolates were multiresistant and harboured the resistance genes that explained the resistance phenotype. The qacG and qacJ genes for biocide resistance were detected in 14 isolates (all MRSA CC398), while 4 isolates (3 CC5 and 1 CC22) had insertions in the -10 motif of the norA promoter. Isolates of the clonal lineages associated with pets (CC5 and CC22) harboured specific sets of virulence genes and often a lower number of resistance genes than isolates of the clonal lineage associated with livestock animals (CC398).

Conclusions: We found, for the first time in animals in Portugal, four strains belonging to CC5, including ST105-II, a lineage that has been previously reported as vancomycin-resistant S. aureus in Portugal. Moreover, for the first time the qacG and qacJ genes were detected in MRSA CC398 strains. Active surveillance programmes detecting MRSA not only in livestock animals but also in companion animals are urgently needed.