A new sequence type identified in methicillin-resistant staphylococci (MRS) in Portugal

Abstract

Methicillin-resistant staphylococci (MRS) pose a challenge to public health, particularly in healthcare-associated infections, where they seriously threaten the effectiveness of antimicrobial therapy. MRS strains have also been implicated in community-associated infections, such as in companion animals, wild animals, fresh foods, and ready-to-eat foods, and livestock-associated infections, such as in poultry and cattle. In this study, the antimicrobial susceptibility profile of one hundred Staphylococcus isolates from canine and feline infections and sixty-two Staphylococcus isolates from raw bovine milk was determined. Isolates with an MRS phenotype were tested for the presence of the methicillinresistance genes, mecA and mecC. MRSA isolates were further characterized by spa typing and whole genome sequenced (WGS) for more in-depth characterization, including the determination of sequence types (ST)/clonal complexes (CC). Six MRS isolates were identified from companion animals, including four S. pseudintermedius, one S. hominis, and one S. haemolyticus, while five S. aureus isolates from raw bovine milk presented an MRS phenotype. The mecA gene was detected as being responsible for the phenotype observed in all of them. The spa types identified were t011 and t2383, which are types normally associated with MRSA isolates in Europe. In turn, all MRSA isolates revealed a new ST, now designated as ST8475. This study reveals the spread of MRS isolates not only in farm animals but also in companion animals, which could pose a risk to public health. Furthermore, not only S. aureus but also S. pseudintermedius, the species most commonly detected in companion animal, appears to be associated with the MRS phenomenon. More importantly, a new ST associated with MRSA isolates has been identified and submitted to the MLST database (ST8475). This could imply the emergence of a new genetic lineage in Portugal, and cattle as a possible reservoir of resistance.