The association of the penicillin-binding component of Staphylococcus aureus with a lipid fraction

Possible mechanism of decreased susceptibility of Neisseria gonorrhoeae to penicillin

By use of (14)C-labeled benzyl penicillin, it has been established that beta-lactamases and/or acylases play no role in the resistance of Neisseria gonorrhoeae to penicillin. It has been found, however, that very susceptible strains of the organisms (minimal inhibitory concentration, 0.008 mug/ml) bind 10 to 15 times as much penicillin as do moderately to highly resistant strains of the gonoccoccus (minimal inhibitory concentration, 0.125 to 2.0 mug/ml). It is postulated that this degree of change in binding components of the whole cell and whole cytoplasmic membrane is sufficient to account for the decreased susceptibility of the organism to penicillin.

Interaction of penicillin with the bacterial cell: penicillin-binding proteins and penicillin-sensitive enzymes

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Correlation between growth inhibition and the binding of various penicillins and cephalosporins to Staphylococcus aureus

The concentration of penicillin (or cephalosporin) required to achieve a given rate of binding to Staphylococcus aureus H correlates well with that required for inhibition of growth. This result suggests that the irreversible binding of penicillins and cephalosporins to cells is responsible for their biological activity.

The inhibition of mucopeptide synthesis by benzylpenicillin in relation to irreversible fixation of the antibiotic by staphylococci

1. Benzylpenicillin is irreversibly fixed to staphyloccoci by a reaction that obeys second-order kinetics, whereas the progress of inhibition of mucopeptide synthesis obeys first-order kinetics after a short lag during which the antibiotic has no effect. 2. When the micro-organisms are saturated with benzylpenicillin they can still make mucopeptide in solutions containing chloramphenicol at a normal rate after a lag period. 3. About 90% of the benzylpenicillin stays fixed to the cells after mucopeptide synthesis has reached its maximum and constant rate. 4. During the phase when mucopeptide synthesis by cells saturated with benzylpenicillin is accelerating, a small number of additional sites that fix benzylpenicillin is revealed. The number of these sites reaches a maximum and constant value at about the same time as mucopeptide biosynthesis reaches a maximum and constant rate. 5. Staphylococci saturated with benzylpenicillin are exceedingly sensitive to fresh additions of the antibiotic. 6. The degree of inhibition of mucopeptide synthesis caused by these small amounts of antibiotic agrees with the degree of substitution by benzylpenicillin of the newly revealed or ;sensitive' sites. 7. Since these sensitive sites are revealed during incubation of the bacteria with chloramphenicol it is unlikely that they are due to newly formed protein. 8. On the basis of these results, a hypothesis for the inhibition by penicillin of the cross-linking reaction in the terminal stages of mucopeptide synthesis is suggested.

Cephalosporinase and penicillinase activities of a beta-lactamase from Pseudomonas pyocyanea

1. Pseudomonas pyocyanea N.C.T.C. 8203 produces a beta-lactamase that is inducible by high concentrations of benzylpenicillin or cephalosporin C. Methicillin appeared to be a relatively poor inducer, but this could be attributed in part to its ability to mask the enzyme produced. Much of the enzyme is normally cell-bound. 2. No evidence was obtained that the crude enzyme preparation consisted of more than one beta-lactamase and the preparation appeared to contain no significant amount of benzylpenicillin amidase or of an acetyl esterase. 3. The maximum rate of hydrolysis of cephalosporin C and several other derivatives of 7-aminocephalosporanic acid by the crude enzyme was more than five times that of benzylpenicillin. Methicillin, cloxacillin, 6-aminopenicillanic acid and 7-aminocephalosporanic acid were resistant to hydrolysis, and methicillin and cloxacillin were powerful competitive inhibitors of the action of the enzyme on easily hydrolysable substrates. 4. Cephalosporin C, cephalothin and cephaloridine yielded 2 equiv. of acid/mole on enzymic hydrolysis, and deacetylcephalorsporin C yielded 1 equiv./mole. Evidence was obtained that the opening of the beta-lactam ring of cephalosporin C and cephalothin is accompanied by the spontaneous expulsion of an acetoxy group and that of cephaloridine by the expulsion of pyridine. 5. A marked decrease in the minimum inhibitory concentration of benzylpenicillin and several hydrolysable derivatives of 7-aminocephalosporanic acid was observed when the size of the inoculum was decreased. This suggested that the production of a beta-lactamase contributed to the factors responsible for the very high resistance of Ps. pyocyanea to these substances. It was therefore concluded that the latter might show synergism with the enzyme inhibitors, methicillin and cloxacillin, against this organism.

The effect of penicillin on the structure of staphylococcal cell walls

Cultures of sensitive stains of Staphylococcus aureus were fixed with osmium tetroxide after 1–5 hours' exposure to various does of pencillin and were embedded in methacrylate for sectioning and electron microscopy. They were compared with untreated, control cultures. The contrast of the cell wall material was untreated, control cultures. The contrast of the cell wall material was increased, by cutting the section of lanthanum nitrate.The cells increased in size and the surrounding cell wall was thinner than normal. The main lesions appeared in the developing cell wall septa, which showed a loss in density and gross irregularity of shape. Some questionable inclusions were seen in the cytoplasm. Lysis was prevented in a medium containing 0.3 M sucrose and the stable spheroplasts retained a recognizable cell wall after 24 hours' exposure to penicillin. However, the septa could not be demonstrated in the cells treated in sucrose medium.Two resistant strains were exposed to penicillin. In one, the cells showed no morphological effects; in the other, there was temporary damage to the cell septa with complete recovery.The observations support the hypothesis that penicillin interferes with the synthesis of a cell wall component and indicate that the main point of cell wall synthesis is at the site of septum formation.