Homologous direct repeat sequences associated with mercury, methicillin, tetracycline and trimethoprim resistance determinants in Staphylococcus aureus

Restriction endonuclease and DNA hybridization analyses of the Staphylococcus aureus plasmid pSK1, which encodes resistance to ethidium bromide (Eb), quaternary ammonium compounds, gentamicin (Gm), kanamycin (Km), tobramycin (Tm) and trimethoprim (Tp), identified three copies of a directly repeated DNA sequence of approx. 1 kb located in the proximity of the Tp-resistance-encoding region of the plasmid. Directly repeated sequences homologous to those detected on pSK1 were also identified on S. aureus heavy-metal resistance (β-lactamase) plasmids and the S. aureus chromosome; in both, these repeats flank related, but not identical, mercury (Hg)-resistance-encoding regions. The chromosomal Hg-resistance region mapped adjacent to an integrated tetracycline (Tc)-resistance plasmid equivalent to pT181, which was also flanked by copies of the repeated sequences, and to a DNA segment associated with methicillin (Mc) resistance.