Chromosomally-encoded gentamicin resistance in 'epidemic' methicillin-resistant Staphylococcus aureus: detection with a synthetic oligonucleotide probe.

A 30 base synthetic oligonucleotide probe to the AAC(6') coding region of the gentamicin resistance transposon Tn4001 was constructed. This was used to probe plasmid extracts and restriction endonuclease (RE) digests of total DNA from epidemic methicillin-resistant Staphylococcus aureus (EMRSA) isolates. Hybridization occurred to plasmid bands of gentamicin-resistant EMRSA which carry a gentamicin resistance plasmid, but not to DNA of gentamicin-sensitive EMRSA. Hybridization also occurred to RE digestion fragments of total DNA from recently-isolated, plasmid-free gentamicin-resistant EMRSA isolates. This confirmed the presence of the gentamicin-resistance gene in the chromosomal DNA of the 'new' EMRSA isolates.