Increase in colony-forming units of Candida albicans after treatment with polyene antibiotics

Abstract

Polyene antibiotics, at concentrations which do not cause detectable toxic effect, induce an increase in the number of colony-forming units of yeast cells of Candida albicans. This effect, which we attribute to an increase in plating efficiency, is probably caused by binding of the polyenes to fatty acids in the cell wall of fungi.The toxic effects of polyene antibiotics on fungi are generally attributed to the binding of the polyenes to cell membrane sterols (4, 11). However, binding can also occur without toxicity (7). In this study we show that under conditions in which polyenes are not toxic to yeast cells of Candida albicans (low concentration of antibiotic, or low incubation temperature), they can increase the number of colony-forming units of the fungus.C. albicans (obtained from L. Haley, Center for Disease Control, Atlanta, Ga.), was grown overnight in liquid Sabouraud medium. Cell viability was at least 97% as estimated by exclusion of trypan blue. The untreated cells, counted in a hemacytometer and then properly diluted, had a plating efficiency of 60 to 70%. That is, the number of colony-forming units on Sabourauddextrose-agar plates after 24 h of incubation at 37°C was 60 to 70% of the cell number counted in the hemacytometer. This plating efficiency was very reproducible in our laboratory and was also normally achieved in the Clinical Mycology Laboratory at Barnes Hospital. More prolonged incubation of the plates did not result in an increase in the number of colonies.To measure the effects of drug, cells were transferred to fresh liquid medium and exposed to the assayed compound for 1 h at 37°C with intermittent shaking. Cells incubated in concentrations of amphotericin B (AmB) lower than that causing detectable K+ leakage, formed more colonies in agar than did untreated cells (Fig. 1).The increase in colony-forming units was 20 to 50% (the mean from 5 experiments was 32 ± 6%), and the resulting plating efficiency was 80 to 95%.Similar increases in colony number were also observed when C. albicans was exposed in liquid medium to nontoxic concentrations of nystatin or filipin. The maximal increase in colony-forming units occurred at a concentration of 0.05 ,ug of nystatin per ml and 1.5 ,ug of filipin per ml. Fifty percent K+ leakage from C. albicans occurred at 0.2 jig of nystatin per ml and 8 ,g/ml of filipin per ml.We think that the increase in colony-forming units was caused by the portion of the polyene molecule which is responsible for the toxic effects. The evidence for this is that inactivation of AmB by exposure to visible light by a procedure previously described (9) or the addition of ergosterol to the cultures containing AmB decreased both of these effects proportionately.Differences in the temperature dependence of the nontoxic and toxic effects of the polyenes made us suspect that they had different mechanisms. AmB binds comparably to yeast at 37 and 2°C (7), but toxicity is greatly diminished at the lower temperature (1, 7). In the present experiments, 30% of intracellular K+ leaked ...

Stimulatory, permeabilizing, and toxic effects of amphotericin B on L cells

“…Thus, treatment with AmB increased plating efficiency by some unknown mechanism. This result is similar to that seen previously with yeast cells (5).…”

“…Increases in DNA, RNA, and protein synthesis have been demonstrated in different cell types (7,9,16,17). A link between stimulatory and ion-permeabilizing effects of AmB has been suggested (26), but polyenes which do not induce K+ leakage from viable cells can potentiate the anticellular action of other agents (1,2) and also enhance the plating efficiency of Candida albicans yeast cells (5).…”

The effects of amphotericin B on the interaction of Candida albicans with fibroblast cultures

“…lA, exposing the yeasts to 0.3 ,ug AmBImL resulted in an increase in cfu over the controls. A similar observation has been reported by Brajtburg et al (1981), who attributed this effect to an enhanced plating efficiency. While 0.3 pg AmBImL was apparently nonlethal to the yeasts, this concentration did inhibit germ tube formation to varying degrees, with the PV-8 isolate appearing to be the least sensitive and the PV-1 and PV-2 isolates the most sensitive.…”

Mechanism of Action of an Anti-Candida Drug: Amphotericin B and Its Derivatives

“…Although the exact dose may vary depending on the experimental conditions, this stimulatory effect has been seen in yeasts treated with 0.01-0.04 p.g/ml AmB, which was attributed to an increase in plating efficiency originating from the AmB binding to fatty acids in the cell wall of the fungi [19]. The intracellular amount of fatty acids has been shown to increase under these conditions [110].…”