Effect of the removal of outer cell wall layers on the actinomycin susceptibility of a gram-negative bacterium

Bactericidal effect of combinations of antimicrobial drugs and antineoplastic antibiotics against gram-negative bacilli

Six antineoplastic antibiotics showed little antibacterial activity against 28 strains of four species of gram-negative enteric bacteria. By using the cellophane transfer technique, combinations of these agents with 16 antibacterial drugs usually showed indifference. However, combinations of mitomycin C, especially with the aminoglycosides, were synergistic on strains of Escherichia coli, Proteus, and Klebsiella pneumoniae. Bleomycin, on the other hand, often showed antagonism on strains of E. coli and K. pneumoniae with the beta-lactams, aminoglycosides, and other antibacterial agents. Checkerboard titrations and kinetic killing curves confirmed these findings.

Multiple antibiotic resistance in clinical strains of Neisseria gonorrhoeae isolated in South Carolina

Minimal inhibitory concentration (MIC) values for penicillin G, tetracycline, amoxicillin, and actinomycin D were determined for 81 strains of Neisseria gonorrhoeae isolated from patients attending public health clinics in the Piedmont region of South Carolina. Gonococcal isolates were also screened for highlevel resistance to streptomycin. Significant positive correlations (r >/= 0.45, P </= 0.01) were found between all possible pairs of the antibiotics penicillin G, tetracycline, and amoxicillin. The MIC values of actinomycin D showed no significant positive correlations with the MIC values of the other antibiotics. Gonococcal strains that were resistant to streptomycin tended to be resistant to penicillin G, tetracycline, and amoxicillin. Of the 81 isolates, 18.5% were multiply resistant to penicillin G, tetracycline, amoxicillin, and streptomycin. Spontaneous mutants with reduced antibiotic susceptibility, selected for decreased susceptibility to penicillin G, displayed small decreases in susceptibility to tetracycline, amoxicillin, and actinomycin D. Spontaneous mutants selected for decreased susceptibility to actinomycin D displayed small losses in susceptibility to penicillin G. The results show that multiple antibiotic resistance occurs in clinically isolated gonococcal strains in South Carolina. The results further suggest the presence of a common genetic mechanism determining antibiotic resistance in N. gonorrhoeae.

Diminution of outer membrane permeability by Mg2+ in a marine pseudomonad

Intact cells of the marine pseudomonad MB-45, in the presence of optimal Mg2+, exhibited little alkaline phosphatase activity as judged by the hydrolysis of p-nitrophenylphosphate. Sonic extracts, in contrast, were rich in this activity. Removal of the loosely bound outer layer did not diminish this crypticity of alkaline phosphatase, but decreasing the concentration of Mg2+ in the suspending medium progressively exposed the alkaline phosphatase. Since MB-45 did not liberate alkaline phosphatase into the surrounding medium even in the absence of Mg2+ and since this enzyme is localized in the periplasmic space, it can be concluded that the crypticity was due to the exclusion of p-nitrophenylphosphate by the outer membrane. Mg2+ is apparently essential for the full expression of this limited permeability.

Ultrastructure of cell envelopes of bacteria of the bovine rumen

Most of the bacteria found in rumen fluid samples taken from cows fed hay, or a concentrate diet, had cell walls of the gram-negative type. Most were intact, with only a small proportion of lysed cells, and many of the cells contained electron-translucent cytoplasmic deposits similar to the carbohydrate reserve material described in pure cultures of rumen organisms. All of the bacteria observed in these samples had an external "coat" layer outside the outer membrane when fixed in glutaraldehyde and osmium, stained with uranyl acetate and lead citrate, and examined as sectioned material. These coat layers varied from thin (ca. 8 nm) structures to very extensive fibrous systems, sometimes including concentric arrangements and radial fibers extending up to 1,200 nm from the cell. The thin-coat layers sometimes exhibited a rough periodicity. In all, 10 different types of coat layers were distinguishable on a morphological basis. It is proposed that these external coat layers have protective and adherence functions for the rumen bacteria in the environment.

Effect of actinomycin D and oxygen on the ribonucleic acid synthesis of an anaerobic gram-negative bacterium

The synthesis of ribonucleic acid by whole cells of Bacteroides ruminicola is not sensitive to actinomycin D, but it is sensitive to actinomycin D in the presence of ethylenediaminetetraacetate. Ribonucleic acid synthesis by whole cells of this gram-negative anaerobic bacterium is also totally inhibited by oxygen.

Structure and function of the cell envelope of gram-negative bacteria

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Susceptibility of whole cells and spheroplasts of Pseudomonas aeruginosa to actinomycin D

Cells of Pseudomonas aeruginosa suspended in 0.2 M Mg(2+), 20% sucrose, 0.01 M tris(hydroxymethyl)aminomethane, or water partially release lipopolysaccharide. The release of alkaline phosphatase from the periplasmic space and the ability to form spheroplasts on lysozyme treatment is directly related to the lipopolysaccharide released during treatment with 0.2 M Mg(2+), 20% sucrose, or other agents. The synthesis of ribonucleic acid (RNA) by intact cells, magnesium-lysozyme spheroplasts, or 20% sucrose-lysozyme spheroplasts is not sensitive to actinomycin D, whereas RNA synthesis by intact cells or spheroplasts in the presence of ethylene-diaminetetraacetic acid (EDTA) is sensitive to actinomycin D. EDTA alone has an inhibitory effect on RNA synthesis by whole cell, by magnesium-lysozyme spheroplasts, and by 20% sucrose-lysozyme spheroplasts. The experimental data indicate that, although the cell wall is damaged by 0.2 M Mg(2+) or 20% sucrose treatment in the presence of lysozyme, the treated cells or spheroplasts are still resistant to actinomycin D. These results suggest that the cytoplasmic membrane should be considered as the final and determinative barrier to this antibiotic in this organism.