Genetic Diversity among Staphylococcus aureus Isolates Showing Oxacillin and/or Cefoxitin Resistance Not Linked to the Presence of <i>mec</i> Genes

Abstract

Methicillin-resistant <i>Staphylococcus aureus</i> isolates lacking <i>mec</i> genes (<i>n</i> = 32), collected from Belgian hospitals, were characterized for their β-lactamase production and the presence of mutations in <i>pbp</i> genes, the <i>pbp4</i> promoter, and genes involved in penicillin-binding protein 4 overproduction (<i>gdpP</i> and <i>yjbH</i>). Twelve isolates were β-lactamase hyperproducers (BHPs), while 12 non-BHP isolates might produce an incomplete GdpP protein. Most isolates showed nucleotide missense mutations in <i>pbp</i> genes. A few isolates also showed mutations in the <i>pbp4</i> promoter.