Extrachromosomal Control of Methicillin Resistance and Toxin Production in Staphylococcus aureus

Abstract

All of 41 naturally occurring coagulase-positive methicillin-resistant strains of Staphylococcus aureus isolated in various laboratories were resistant to several antibiotics and were lipase-negative. Most strains produced hemolysins, and 38 strains produced enterotoxin B. Acriflavine treatment of four strains resulted in elimination of resistance to methicillin and mercury; in one strain, resistance to cadmium was also lost. Production of enterotoxin B and β-hemolysin was eliminated in all four strains and penicillinase production was eliminated in one strain. In transduction experiments, methicillin resistance and enterotoxin B production were transferred together at a frequency of 0.2 × 10 −8 to 1.1 × 10 −8 by use of ultraviolet-induced phage lysates from naturally lysogenic methicillin-resistant strains. Cotransductions of resistance to mercury and cadmium, as well as production of penicillinase and β-hemolysin, were obtained to some extent. The extrachromosomal character of these determinants and their possible genetic association are discussed.