SOME ASPECTS OF THE MODE OF ACTION OF POLYENE ANTIFUNGAL ANTIBIOTICS

Effects of subinhibitory dose of amphotericin B on cell wall biosynthesis in Candida albicans

Subinhibitory doses of amphotericin B in the culture medium of Candida albicans modified yeast cell wall synthesis. Analysis of isolated cell walls showed a decrease in mannose and an increase in amino acid and glucosamine levels. After fractionation of the cell wall by ethylenediamine or pronase digestion, study of the fractions corroborated an outer phosphopeptidomannan decrease and an enrichment of matrix constituents. Determination of the amount of chitin showed stimulation of synthesis of this amino polysaccharide in yeasts grown in the presence of amphotericin B. Decrease in phosphopeptidomannans and high production of other cell wall constituents are probably consequences of modification of the lipidic environment of membrane-bound enzymes by the antifungal polyene action.

[Effect of a subinhibitory dose of amphotericin B on cellular fatty acid and sterol composition of Candida albicans]

Modifications in the cellular lipids of Candida albicans VW32 during its growth in the presence of a subinhibitory dose of amphotericin B were studied. Intracellular accumulation of fatty acids which appeared during growth was retarded in the presence of this antifungal agent after initial stimulation of unsaturated fatty acids. During the growth stage of the yeasts, sterols accumulated in cells through the action of amphotericin B. This accumulation was 80% during the growth state, but was only 13% in the stationary state. The relative level of ergosterol decreased through the action of this antifungal agent, but its precursors, namely ergosta-5,7-dien-3 beta-ol, episterol and fecosterol increased. The higher oxygenation of the cells due to the effect of this antifungal agent appeared to be responsible for the accumulation of unsaturated fatty acids and sterols in growing cells.

Effect of amphotericin B on the metabolism of Aspergillus fumigatus

Action of amphotericin B on the growth and metabolism of Aspergillus fumigatus has been investigated. The fungus proved to be very sensitive to amphotericin B, showing complete inhibition of growth at 0.5 units/ml. Amphotericin B suppressed the exogenous and endogenous respiration and glycolysis of A. fumigatus as well as the assimilation of various glycolysis and TCA cycle intermediates. Addition of cations and cholesterol failed to reverse the action of amphotericin B. The treated mycelium released a variety of cellular constituents and it is inferred that the antibiotic effects the permeability of A. fumigatus cells. In experiments with 32P labelled mycelium phosphorus compounds leached out in concentrations which were dependent on the antibiotic dose, period of contact, incubation temperature and metabolic state of the fungus.

Effect of antibodies on the respiration and morphology of Candida Albicans

Respirometry was used to study the effect of antibodies to Candida albicans on the gowth of this species in vitro. Blastospore suspensions were pre-incubated with rabbit hyperimmune and normal serum and rabbit antibody and normal gamma globulin at 37 degrees C for 30 minutes. They were then inoculated into respirometer flasks containing a semi-synthetic medium and oxygen consumption was measured at 27 degrees C. Rabbit antiserum to C. albicans serotype A inhibited the growth, as measured by O2 consumption, of serotyped A and B strains of C. albicans. The amount of inhibition appeared to be related to the prevention or retardation of germ tube formation. The growth of blastospores incubated with normal rabbit serum was filamentous, whereas, blastospores incubated with antiserum remained in the yeast phase. Inhibition of O2 consumption and retardation of germ tube formation was also demonstrated with the purified gamma-globulin fraction of the antiserum.

EFFECTS OF SODIUM CAPRYLATE ON CANDIDA ALBICANS II

Payne , W. J. (University of Georgia, Athens) and E. R. Bannister . Effects of sodium caprylate on Candida albicans . II. Influence of various concentrations on biochemical changes. J. Bacteriol. 86: 558–562. 1963.—Suspending resting cells of Candida albicans in buffered solutions of 0.1 m sodium caprylate resulted in leakage of K + , protein, ribonucleic acid (RNA), and carbohydrate (including glucose) but not of deoxyribonucleic acid (DNA) or sterol. In 0.025 m caprylate, the yeast leaked carbohydrate but not any of the other metabolites, whereas at 2.5 × 10 −3 m or in buffer alone there was no significant leakage. Inclusion of 2.5 × 10 −3 m sodium caprylate in Sabouraud dextrose broth cultures, however, suppressed growth greatly. Assays of relative protein, RNA, and DNA contents of dried cells taken from the suppressed cultures revealed changes in the rates of production of each from those of untreated cultures.