Progress of O-acetylation and cross-linking of peptidoglycan in Neisseria gonorrhoeae grown in the presence of penicillin

The synthesis, cross-linking and O-acetylation of gonococcal peptidoglycan in growing cells were studied by following incorporation of radioactive glucosamine and separation of the SDS-insoluble peptidoglycan into uncross-linked (monomer) and cross-linked (dimer and oligomer) fragments. Cultures to which penicillin or piperacillin at concentrations near the minimum growth inhibitory concentration (MIC) had been added 20 min before the radioactive label were compared with controls. The beta-lactams affected the early stage of cross-linking (up to 3 min) but had no effect thereafter. The deficit of cross-linking, however, did not recover. The O-acetylation, particularly of the monomer fraction, was decreased by beta-lactams even at concentrations that had no effect on culture optical density, viable counts or overall peptidoglycan synthesis. These effects on O-acetylation occurred mainly after the first 3 min of incorporation, rather than before. O-Acetylation of the oligomer fraction was also followed. Here penicillin led to increased levels of O-acetylation during the early stages of incorporation but the final value was never exceeded; indeed at higher drug concentrations the later stages of O-acetylation of oligomers were inhibited (e.g. almost completely at 2.5 X MIC).