[Changes in the cell wall of Candida albicans cultivated in the presence of sublethal doses of nystatin]

"Giant" blastoconidia of Candida albicans: morphologic presentation and concepts regarding their production

Candida albicans normally produces blastoconidia measuring 2 to 8 microns in diameter. Markedly enlarged "giant" (approximately 30 microns) blastoconidia of a C. albicans isolate (designated BH) were observed after growth on commercially prepared chocolate agar already supplemented with IsoVitalex (BBL-Microbiology Systems, Cockeysville, MD, USA). Morphologically, "giant" blastoconidia presented a spectrum of forms such as blastoconidia with linear creases, with a single broad-based bud resembling Blastomyces dermatididis, with multiple buds resembling Paracoccidioides brasiliensis, or elliptical in shape. "Giant" blastoconidia contained a large oval clear vacuole occupying greater than 50% of the blastoconidium. Pseudohyphae emanating from these blastoconidia were also enlarged and contained a similar oval inclusion. Rarely observed were "giant" blastoconidia with either adherent or internalized blastoconidia uniformly arranged within the blastoconidium. "Giant" or enlarged blastoconidia production was constant, usually approaching 10 to 20% of the blastoconidial units comprising a single colony, irrespective of the number of subcultures. IsoVitalex supplementation of Remel (Lexana, KS, USA) chocolate agar but not a variety of other media also resulted in "giant" blastoconidia production. It is, therefore, theorized that a component(s) of IsoVitalex activates/blocks a gene present in select clones of C. albicans blastoconidia resulting in "giant" or enlarged blastoconidiogenesis.

Activity of cilofungin (LY 121019), a new lipopeptide antibiotic, on the cell wall and cytoplasmic membrane of Candida albicans. Structural modifications in scanning and transmission electron microscopy

Cilofungin, a new biosemisynthetic analog of echinocandin B, inhibits the synthesis of beta-(1,3)-glucan resulting in severe modifications of the cell wall and cytoplasmic membrane of sensitive organisms. The morphological modifications to budding yeast cells, pseudomycelium, mycelium and germ tubes of Candida albicans were studied by scanning and transmission electron microscopy after 3 and 16 h exposure to cilofungin. Changes in yeast cell morphology were apparent after 3 h in 0.1 microgram ml-1 cilofungin but were more marked in 1 and 10 micrograms ml-1 cilofungin. Most of the yeasts failed to separate and formed aggregates. Cracks and discontinuities were present in the cell wall and the cell membrane became undulated and fractured. Inclusions into the periplasmalemma space were observed, along with a release of cellular components. An important inhibition of germ tube formation was noted and the structure of true mycelium and pseudomycelium was severely modified. The budding area of yeast cells was particularly susceptible to damage by cilofungin.

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.