Cell envelope of Neisseria gonorrhoeae: penicillin enhancement of peptidoglycan hydrolysis

Abstract

The addition of 10 microgram of penicillin G per ml to log-phase cultures of Neisseria gonorrhoeae JW-31 (minimum inhibitory concentration for penicillin G, less than 0.007 microgram/ml) resulted in cellular lysis after a lag of 30 min. Penicillin markedly decreased the rate of peptidoglycan synthesis and enhanced the rate of hydrolysis of existing peptidoglycan. Hydrolysis was initiated immediately after addition of penicillin; cellular lysis did not occur until a considerable percentage of the peptidoglycan had been degraded. Cellular lysis was not due to penicillin per se but resulted from inhibition of cell wall synthesis. When cells were grown in media buffered with N-2-hydroxyethyl piperazine-N'-2-ethanesulfonic acid at pH 6, penicillin did not cause lysis; however, at this pH, peptidoglycan hydrolysis occurred and cells lost viability at the same rate as in the control (pH 7.2). We suggest that the stability of gonococci grown at pH 6 is related to increased stability of the outer membrane. The penicillin-enhanced rate of peptidoglycan hydrolysis decreased approximately 50% at pH 6.0. Penicillin-enhanced lysis, peptidoglycan hydrolysis, and loss of viability were also markedly reduced in cells grown at 28 degrees C.