Penicillinase production and intrinsic resistance to penicillins in Staphylococcus aureus

METHICILLIN is relatively insusceptible to the action of staphylococcal penicillinase, but naturally occurring strains of Staphylococcus aureus that are resistant to methicillin usually produce large quantities of the enzyme. Staphylococcal penicillinase does hydrolyse methicillin slowly (Novick, 1962), and it therefore seemed possible that methicillin resistance might be due in part to the inactivation of methicillin. Stewart and Holt (1963) and Eriksen and Erichsen (1 964) reported that methicillin-resistant strains were capable of a greater inactivation of methicillin than were methicillin-sensitive strains, but Richmond et al. (1964) found no difference between the average amount of penicillinase produced by methicillin-resistant staphylococci and by other multiple-antibiotic resistant but methicillin-sensitive " hospital " staphylococci. Penicillinase could play only a minor role in the resistance to methicillin of the cultures examined by Baudens, Gerbaud and Chabbert (1965), by Dyke, Jevons and Parker (1966) and by Seligman (1966a), since variants that had lost the ability to synthesise penicillinase showed levels of resistance to methicillin similar to those of the parent strains. It appears