Iron-limited biofilms of Candida albicans and their susceptibility to amphotericin B

Abstract

Biofilms of Candida albicans were grown in vitro under iron limitation and at a low growth rate to simulate conditions for implant-associated biofilms in vivo. Their properties were compared with those of glucose-limited biofilms grown under analogous conditions. At steady state, the adherent cell populations of iron-limited biofilms were double those of glucose-limited biofilms, although the growth rates were similar (0.038 to 0.043 h-1). Both biofilm types were resistant to amphotericin B, but daughter cells from iron-limited biofilms were significantly more susceptible to the drug than those from glucose-limited biofilms.

FIG. 1

Elution of C. albicans from cylindrical cellulose filters perfused with iron-limited (•) or glucose-limited (○) growth medium at a flow rate of 0.87 ml min⁻¹. Results are means from two independent experiments carried out with duplicate sampling. Standard errors were less than 10% of means.

FIG. 2

Scanning electron micrographs of C. albicans biofilms grown for 24 h on cylindrical cellulose filters perfused with iron-limited (A) or glucose-limited (B) growth medium. Biofilms were prepared for microscopy as described previously (14) except that they were air dried overnight. Bar, 10 μm.

FIG. 3

Survival of biofilm cells of C. albicans grown in iron-limited or glucose-limited medium after treatment with amphotericin B. Intact biofilms (▧), resuspended biofilm cells (), and biofilm daughter cells (□) were exposed to amphotericin B for 1 h, and the percent survival was estimated by viable counts. Results are means ± standard errors of the means from three independent experiments with viable counts done in triplicate.