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At least 577 records · Page 32Linked to original sources
PubMed1993

Basic mechanisms of bacterial tolerance of antimicrobial agents.

Although it has been known for many years that beta-lactam antibiotics inhibit the synthesis of peptidoglycan, it was the phenomenon of tolerance which allowed elucidation of the mode of action of beta-lactam antibiotics particularly with respect to the lysis of the bacteria. By studying tolerant pneumococci it was shown that penicillin triggers the production of autolytic enzymes which degrade the peptidoglycan to such an extent that lysis and killing of cells occurs. Since this discovery many studies have shown that various microorganisms are capable of preventing the lysis and/or killing action of beta-lactams. In Staphylococcus aureus strains, for instance, tolerance appears to be due to the lower specific activity of autolytic enzymes, extracted after exposure to a high concentration of methicillin (64 micrograms/ml). At these high concentrations of beta-lactams the same strains also show inhibition of RNA and protein synthesis. This inhibition of macromolecular synthesis is probably due to a feed-back mechanism which synchronizes synthesis rates of protein, RNA, peptidoglycan and the activity of autolytic enzymes.

Anti-Bacterial Agents↗
PubMed1995

From growth to autolysis: the murein hydrolases in Escherichia coli.

Murein hydrolases cleave bonds in the bacterial exoskeleton, the murein (peptidoglycan) sacculus, a covalently closed bag-shaped polymer made of glycan strands that are crosslinked by peptides. During growth and division of a bacterial cell, these enzymes are involved in the controlled metabolism of the murein sacculus. Murein hydrolases are believed to function as pacemaker enzymes for the enlargement of the murein sacculus since opening of bonds in the murein net is needed to allow the insertion of new subunits into the sacculus. Furthermore, they are responsible for splitting the septum during cell division. The murein turnover products that are released during growth are further degraded by these (1 --> 6)-anhydromuramic acid derivatives by an intramolecular transglycosylation reaction.

Bacteriolysis↗
PubMed1990

Lytic effect of Vibrio cholerae elastase on gram-positive and -negative bacteria.

Elastase of Vibrio cholerae caused the lysis of freshly grown cells of Gram-negative (Pseudomonas aeruginosa, Proteus vulgaris, Salmonella paratyphi A and Klebsiella pneumoniae) bacteria. Gram-positive (Staphylococcus aureus and S. epidermidis) organisms were resistant to this enzyme. Heat killed and lyophilized Gram-positive and -negative bacteria (except S. aureus and S. epidermidis) showed higher sensitivity to elastase. Both Gram-negative and -positive bacteria were lyzed maximally by elastase at pH 8.0. At this pH, lytic activity of elastase was maximum in Tris-HCl and glycine-NaOH buffers followed by Tris-maleate and cacodylate buffers.

Bacteriolysis↗
PubMed1980

Visualization of membrane-associated R-plasmid DNA in fraction of Escherichia coli minicell lyzate.

Minicells of Escherichia coli P678-54 containing plasmid RIdrd19 were submitted to careful controlled lysis. By sedimentation of the resulting lyzate in a sucrose gradient, the material absorbing at 260 nm was separated into three distinct bands. Among the most rapidly sedimenting particles, double-stranded topological circles of DNA attached to patches of membrane were visualized by electron microscopy, while single-stranded molecules (probably RNA) with associated proteins were detected in the medium band. Covalently closed and open circles of the RIdrd19 DNA were found at the top of the gradient. Their contour lengths correspond to the size of the DNA sedimenting together with the membrane in the first peak. This finding implies a direct intracellular interaction between RIdrd19 DNA and membrane in E. coli minicelle.

Bacteriolysis↗
PubMed1975

Electron-microscopic study of a Mycoplasmatales virus, strain MV-Lg-pS2-L 172.

Morphology and adsorption of a globular virus, lysing Acholeplasma laidlawii were studied in ultrathin sections of plaques in a lawn of the host strain. The virus was globular, about 50 to 90 nm in diameter, with a clearly defined membrane, 6.5 to 8 nm thick. A protuberance about 25 to 35 nm long and 12 to 20 nm thick was observed on numerous virus particles. The evenly granulated, electron-optically dense content of the cells became clearer in cells affected by the viruses. Fibrillar structures of different thickness and small dense areas appeared in cells assumed to be in the preliminary stages of lysis. The interactions in the virus-host system and possible development stages of the virsu are discussed.

Acholeplasma laidlawii↗