Anomalous cellular morphology and growth characteristics of Neisseria meningitidis in subminimal inhibitory concentrations of penicillin G

The effects of subminimal inhibitory concentrations of penicillin G on Neisseria meningitidis in the presence and absence of selected stabilizers were examined. Subminimal inhibitory concentrations of penicillin G decreased cell numbers and altered both colonial and ultrastructural morphologies of this meningococcus. Although these levels of penicillin did not have immediate adverse effects on cell mass increase, deoxyribonucleic acid synthesis, or the incorporation of [3H]leucine into protein, they did significantly alter the division rate and the integrity of the cell envelope. The inability of many of the abnormal membranous cell types produced in subminimal inhibitory concentrations of penicillin to form either complete or properly oriented division septa and the overproduction of cell wall material at such sites was indicative of the disruptive effects of this antibiotic on functions necessary for maintaining the normal division process. The addition of the stabilizers polyvinylpyrrolidone-40 and horse serum to the test medium diminished the effects of penicillin G as evidenced by a fourfold increase in the minimal inhibitory concentration. Moreover, such stabilizers maintained the association of the outer membrane with the peptidoglycan and inner membrane.