The action of ampicillin on Aerobacter (Klebsiella) aerogenes

Abstract

Abstract The action of ampicillin (α-aminobenzylpenicillin) on Aerobacter (Klebsiella) aerogenes (NCTC 418, Bact. aerogenes no. 240) has been investigated. Enzymatic destruction of the drug, although a necessary prelude to the growth of the sensitive strain, does not precede growth of resistant strains at concentrations to which they have been “conditioned”. Instead a gradual inactivation occurs throughout the growth cycle. It is concluded that other factors are also involved in resistance. Cloxacillin, which was not destroyed by the cells, had little action on the ampicillin-sensitive strain and did not induce any ampicillin-destroying activity. The results are discussed in terms of the modes of action of penicillins and the origin of the resistance is examined.