No abstract

The cellular morphology of a biochemical variant of Candida albicans could be controlled by the ratio of carbon dioxide to oxygen in the culture system or by individual amino acids. Predominantly pseudohyphal morphology was observed (i) at a CO2 to 02 ratio of 2:1 and (ii) without the addition of carbon dioxide, when either glycine, Dor L-ornithine, L-serine, L-methionine, L-phenylalanine, or L-tyrosine was the sole nitrogen source in the culture medium. When ammonium chloride, ammonium sulfate, L-glutamic acid, L-glutamine, or L-proline was the nitrogen source, yeastlike growth was observed in the presence or absence of CO2. More adenosylmethionine was present in pseudohyphal than in yeastlike cells, and pseudohyphal cell wall preparations contained less methionine than cell walls from the yeastlike form. These results suggest a correlation between sulfur amino acid metabolism and dimorphism.

The lethal response in mice to yeast-like cells of Candida albicans grown for 3, 6, or 9 h in a defined minimal culture medium was more severe than that observed with corresponding pseudohyphal preparations. This differential effect could be only partially correlated with the greater number of viable units in respective yeast-like cultures. No significant differences between yeast-like and pseudohyphal syspensions were detected when turbidity-mass ratios were examined. The injection of physiological saline suspensions containing increasing quantities of yeast-like cells resulted in proportional decreases in mouse survival times. Conversely, when comparable experiments were conducted with pseudohyphal preparations no significant decreases in survival times occurred. The data indicate that these differences in the lethal response cannot be explained solely on the basis of a variation in the number of viable units or cell mass in corresponding yeast-like and pseudohyphal preparations. Factors contributing to this phenomenon may therefore include altered susceptibilities to host defense mechanisms in the early stages of the infectious process as a result of differences between these yeast-like and pseudohyphal inocula.

Lethality of Candida albicans was monitored in (C57BL times DBA/2)F1 mice bearing the transplanted Lewis lung carcinoma and in sham-operated controls inoculated with Hanks' balanced salt solution. The lethal response to C. albicans infection was significantly delayed in animals inoculated with the microorganism 6-16 days after transplantation of the Lewis lung carcinoma. Maximal increases in survival times were observed when C. albicans was inoculated 8-12 days following tumor transplantation. Therefore, a delay in the lethal response to C. albicans in this untreated model murine tumor system could be elicited through implantation of the Lewis lung carcinoma; preliminary studies with some other model murine tumors and with cell-free filtrates indicated that this phenomenon is not restricted to the Lewis lung carcinoma.