A resistance determinant to nucleic acid-binding compounds in methicillin-resistant Staphylococcus aureus.

Recent isolates of methicillin-resistant Staphylococcus aureus from Australia and several other countries carry a plasmid coding for high levels of resistance to propamidine isethionate and low levels of resistance to cetyltrimethyl-ammonium bromide. The reasons for the acquisition and retention of such a determinant are not known. To define the properties of this resistance determinant in more detail, the minimum inhibitory concentrations of a series of cationic agents, including ethidium bromide, were determined and a cationic-resistance profile prepared for several strains of S. aureus and their isogenic, sensitive derivatives. The compounds for which resistance is coded by this determinant all bind to nucleic acids. Hence the determinant has been designated the NAB (nucleic acid-binding compounds)-resistance determinant.