A plasmid that encodes three genes for resistance to macrolide antibiotics in<i>Staphylococcus aureus</i>

Abstract

In previous letters, FEMS Microbiol. Lett. 148 (1997) 91-96, it was demonstrated that plasmid pMS97-obtained from a in 1971 clinically isolated Staphylococcus aureus strain MS8968 resistant to macrolide (Mac) antibiotics--carried an msrA gene and uncharacterized erm gene, respectively. msrA encodes a cytoplasmic membrane protein that mediates the so-called 'active Mac-efflux' (designated hereafter as msrSA') and erm encodes a methyltransferase by which a specific adenine residue of 23S rRNA is modified: methylation prevents Mac antibiotics from binding to the 50S ribosomal subunit. Interestingly, we found, in addition, an mph-like gene (hereafter referred to as mphBM) present together with msrSA' and erm on pMS97. By a BLASTP analysis, the gene mphBM product has 49% identity and 67% similarity to the amino acid sequence of MPH(2')II encoded by mphB from Escherichia coli. The order of genes was 5'-msrSA'-mphBM-3', with a 342-base-pair spacer sequence. Although we have not yet determined where erm gene is located on pMS97, the gene seems to be downstream from mphBM. This finding suggests a warning to us concerning the imprudent use of antibiotics.