EFFECT OF PENICILLIN ON THE MORPHOLOGY OF A NEISSERIA MENINGITIDIS STRAIN NOT LIBERATING FREE ENDOTOXIN

A strain of Neisseria meningitidis which did not release filtrable endotoxin during in vitro growth was treated with 100 times MIC values of benzylpenicillin. After 2 h of exposure to penicillin, most of the bacterial cells were plasmolysed, and only a few bacteria were alive after 20 h. The peptidoglycan layer could be demonstrated in samples investigated after 2 h of penicillin treatment, but was undetectable after 20 h. Only a few outer cell wall structures, small enough to be filtered through a 0.45 micrometer filter were separated from the bacterial cells. Such structures could be observed in all samples studied, both untreated as well as treated cells cultures. This observation corresponded well to the very low content of free endotoxin in filtrates from the samples. Adhesiveness between completely divided cells and between aggregates of cells and cell wall structures was a characteristic finding in the untreated control cultures, but penicillin treatment seemed to amplify this tendency.