Effect of penicillin on the morphology of a Neisseria meningitidis strain not liberating free endotoxin. An electron microscopy study

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.

Effect of penicillin on the morphology of a Neisseria meningitidis strain liberating free endotoxin. An electron microscope study

An endotoxin-liberating strain of Neisseria meningitidis plasmolysed extensively after 2 h of exposure to 100 times MIC values of benzypenicillin. The peptidoglycan layer could be demonstrated after 2 h of treatment in places where the cytoplasm still was close to the cell wall. After 20 h, however, this layer was complete undetectable. In untreated cells the peptidoglycan layer could more easily be found in older cultures than in very young cultures. An increased adhesiveness and aggregation to other bacterial cells and to cell wall material could be observed after 2 h of penicillin treatment, and more pronouncedly after 20 h. A high yield of free cell wall material could be demonstrated after 2 h of penicillin treatment. This corresponded well to an increased content of free endotoxin in the filtrates from the cell cultures treated with penicillin, compared to untreated controls. After 20 h of treatment, free cell wall material had formed large aggregates or was adherent to the cell walls of ghost cells. The corresponding endotoxin analysis showed a reduced content of filtrable endotoxin. Possible implications of the structural changes in relation to penicillin treatment of patients are discussed.

Loss of sulfonamide resistance in Neisseria meningitidis

Four strains of Neisseria meningitidis were studied during serial passage. From two strains which originally were sulfonamide resistant, variants developed that had altered susceptibility to sulfonamides. One of the variants became relatively highly sulfonamide-sensitive, the other exhibited merely reduced sulfonamide resistance. There was a difference in the resistance pattern for two sulfonamides (sulfaisodimidine and sulfamethoxazole), and the effect of inoculum size and growth conditions in three different media could be demonstrated. Although the patterns of susceptibility to other antibacterial agents were different for the strains studied, no further susceptibility alterations occurred in parallel to the sulfonamide sensitivity changes. The variants also lost their ability to liberate free endotoxin.

Loss of endotoxin liberation in Neisseria meningitidis

Four strains of Neisseria meningitidis were studied during serial passage. Upon subcultivation, two of them lost the ability to liberate endotoxin. Ultrastructurally, the two parent endotoxin liberating strains exhibited quantitatively more free cell wall membranes and blebs in the medium than their non-liberating variants. Similarly, the endotoxin-releasing original strains exhibited higher sulfonamide resistance than their variants, and had markedly more sticky cells, which showed pronounced adherence to the surfaces of plastic and heated blood agar.

Release of endotoxin from Neisseria meningitidis. A short survey with a preliminary report on virulence in mice

Gram-negative bacteria release various amounts of cell wall fragments containing endotoxin into the surroundings. The authors demonstrated that liberation of endotoxin from Neisseria meningitidis during growth varied with strain and growth conditions and was dependent on whether the strains released large quantities of cell wall fragments into the medium or not. The ability to liberate endotoxin could be lost upon subcultivation and was associated with certain traits. The experiments indicated that short-lasting therapy with a penicillin dose big enough to give a rapid bactericidal effect increased the release of free, filtrable endotoxin from endotoxin liberating meningococci, but not from a non-liberating variant. This effect was not found when the meningococci were treated with chloramphenicol. The endotoxin liberating meningococcal strains were more virulent for mice than the non-liberating variants, indicating that the tendency to liberate cell wall fragments containing endotoxin may be a factor in the pathogenesis of meningococcal disease in mice.

The endotoxin-liberating effect of antibiotics on meningococci in vitro

Three strains of Neisseria meningitis (two endotoxin-liberating and one in vitro variant non-liberating) were studied during treatment with MIC and 100 times MIC values of benzylpenicillin and chloramphenicol in a chemically-defined, protein-free medium. Treatment with the highest dose of benzylpenicillin had the most rapid effect on meningococci, although the antibacterial effect was the same for the two penicillin concentrations after 20 h. Chloramphenicol treatment showed a much slower antibacterial effect. After 2 h of antibacterial treatment, an increase of filtrable endotoxin in the medium was found for the endotoxin-ligerating strains only when the highest penicillin dose was used. During the same period there was a rapid cell death. After 20 hours of treatment, however, the endotoxin-liberating strains treated with high and low concentrations of penicillin had a markedly reduced content of filtrable endotoxin, compared to the controls and to the cultures treated with chloramphenicol. Antibacterial treatment had no, or only minimal, effect on the total content of endotoxin in the cultures, compared to the untreated controls. The endotoxin non-liberating strain had about the same total content of endotoxin as the liberating strains, but did not liberate filtrable endotoxin into the medium unless filtered with a much higher pressure through a filter with smaller pore size.

The interaction of penicillin and chloramphenicol against meningococci in vitro

Combinations of penicillin and chloramphenicol are frequently used initially in the treatment of bacterial meningitis. The simultaneous effects against meningococci of these two drugs were examined in vitro in a chemically defined, proteinfree medium. The investigation was performed with different combinations of the antibiotics, including optimal concentrations. In most instances, penicillin and chloramphenicol seemed to have an additive, but not an iso-additive, effect. No antagonism was found, and only one out of nine strains showed indifference.

Electron microscopical study of Neisseria meningitidis releasing various amounts of free endotoxin

A study has been made of the ultrastructure of four strains of Neisseria meningitidis which liberate varying amounts of free endotoxin in a chemically-defined, protein-free medium. The two strains which did not release detectable or only sparse amounts of free, filtrable endotoxin were rather uniform in cell size. Their cells appeared to be intact and showed a low tendency to aggregate, In addition cells of these strains showed only sporadic loose, trilaminar membranes and blebs, and free membranous structures were sparse in the medium. The endotoxin releasing strains liberated a high yield of free structures from the outer cell wall into the medium. These structures may represent the lipopolysaccharide (LPS).

Mortality in meningococcal infections

Among 124 patients with meningococcal infections between 1966-1976, 108 had meningitis with a fatality rate of 7.4%, and 16 septicaemia with 18.8% fatality. High risk patients (more than 3 prognostically unfavourable characteristics) increased from 3.5% 1966-1970 to 15.6% 1971-1976, and the total mortality from 3.6 to 10.4%. The most unfavourable prognostic factor was low blood pressure at admission. High risk patients were more common among those who had meningococci with complete or partial sulfonamide resistance (25.7%) than among those having sensitive meningococci (11.9%). When the meningococci were at least partially sulfonamide-resistant, initial therapy with the combination of benzylpenicillin, sulfaisodimidine and chloramphenicol seemed to be more successful than benzylpenicillin alone in patients above 10 years. Ampicillin was used only in children, and these all survived.

Liberation of endotoxin during growth of Neisseria meningitidis in a chemically-defined medium

Modified medium 199 is well suited to the growth of meningococci if rich growth is not necessary. The bacteria were very sensitive to changes in pH and needed a good buffer capacity of the medium. Four strains of Neisseria meningitidis were studied. After the stationary phase had been reached, the vital cell count decreased relatively slowly. However, the total cell count remained unchanged for at least 12 hours. The standardized E. coli endotoxin could be detected easily by the Limulus lysate test in different protein-free, pH-adjusted and ion-balanced liquids, and the determination of endotoxin was reproducible. The Limulus lysate test was more sensitive than the rabbit pyrogen test as regards meningococcal endotoxin. Liberation of endotoxin during growth in modified medium 199 varied with strain and growth conditions. Repeated investigations showed the same pattern of growth and endotoxin liberation for each strain, also under other growth conditions. When sonicating the bacteria, high yields of endotoxin were obtained from each strain.