Effects of beta-lactam antibiotics on peptidoglycan synthesis in growing Neisseria gonorrhoeae, including changes in the degree of O-acetylation

Abstract

Low concentrations of beta-lactam antibiotics caused an increased uptake of radioactive glucosamine into the sodium dodecyl sulfate-insoluble peptidoglycan of growing Neisseria gonorrhoeae. There was no appreciable change in the (small) amount of sodium dodecyl sulfate-soluble polymer present in the cultures. The sodium dodecyl sulfate-insoluble product in control cells was only partially dissolved by egg-white lysozyme (about 40%), but could all be released by the Chalaropsis B muramidase. In cells exposed to beta-lactams the proportion of labeled peptidoglycan susceptible to lysozyme increased to 60%. Examination of the Chalaropsis B digests by thin-layer chromatography showed that they contained disaccharide-peptide monomers with and without O-acetylation and bis-disaccharide-peptide dimers with one or two O-acetyl groups, or with none. beta-Lactam antibiotics caused a decrease in the degree of O-acetylation but did not greatly affect the amount of peptidoglycan cross-linking. They also had the effect of enlarging the bacteria and conserving and thickening the septa that could be observed in thin sections under the electron microscope. The relationship between these results and the effects of beta-lactams on in vitro synthesis of peptidoglycan by ether-treated N. gonorrhoeae is discussed.