Effects of aspirin and other nonsteroidal anti-inflammatory drugs on biofilms and planktonic cells of Candida albicans

Abstract

Prostaglandins are now known to be produced by Candida albicans and may play an important role in fungal colonization. Their synthesis in mammalian cells is decreased by inhibitors of the cyclooxygenase isoenzymes required for prostaglandin formation. In the present study, a catheter disk model system was used to investigate the effects of nonsteroidal anti-inflammatory drugs (all cyclooxygenase inhibitors) on biofilm formation by three strains of C. albicans. Seven of nine drugs tested at a concentration of 1 mM inhibited biofilm formation. Aspirin, etodolac, and diclofenac produced the greatest effects, with aspirin causing up to 95% inhibition. Celecoxib, nimesulide, ibuprofen, and meloxicam also inhibited biofilm formation, but to a lesser extent. Aspirin was active against growing and fully mature (48-h) biofilms; its effect was dose related, and it produced significant inhibition (20 to 80%) at pharmacological concentrations. Simultaneous addition of prostaglandin E(2) abolished the inhibitory effect of 25 or 50 micro M aspirin. At 1 mM, aspirin reduced the viability of biofilm organisms to 1.9% of that of controls. Surviving cells had a wrinkled appearance, as judged by scanning electron microscopy, and consisted of both yeasts and hyphae. Treatment with other cyclooxygenase inhibitors, such as etodolac, resulted in biofilms that consisted almost entirely of yeast cells. In conventional assays for germ tube formation, these drugs produced significant inhibition, whereas aspirin had little effect. Our findings suggest that cyclooxygenase-dependent synthesis of fungal prostaglandin(s) is important for both biofilm development and morphogenesis in C. albicans and may act as a regulator in these physiological processes. Our results also demonstrate that aspirin possesses potent antibiofilm activity in vitro and could be useful in combined therapy with conventional antifungal agents in the management of some biofilm-associated Candida infections.

FIG. 1.

Effects of different concentrations of aspirin on biofilm formation by C. albicans GDH 2346. Biofilm formation (as measured by XTT reduction) is expressed as a percentage of that of control biofilms incubated in the absence of aspirin. Most results are means ± standard errors of the means of at least two independent experiments with a total of seven or more replicates. Results for 250 and 500 μM aspirin are means ± standard errors of the means of triplicate determinations. The mean ± standard error of the mean control value (A₄₉₂) was 2.212 ± 0.084.

FIG. 2.

Scanning electron micrographs of C. albicans GDH 2346 biofilms grown on PVC catheter disks for 48 h in the presence of 1 mM aspirin. (A) Control biofilm; (B) aspirin-treated biofilm; (C) enlargement of marked square in panel A; (D) enlargement of marked square in panel B. Arrows indicate the smooth surface of a control cell (C) and the wrinkled surface of an aspirin-treated cell (D). Bars, 8 μm (A and B) and 1 μm (C and D).

FIG. 3.

Scanning electron micrographs of C. albicans GDH 2346 biofilms grown on PVC catheter disks for 48 h in the presence of no inhibitor (A), 1 mM piroxicam (B), 1 mM indomethacin (C), or 1 mM etodolac (D). Bars, 8 μm.

FIG. 4.

Effects of COX inhibitors (final concentration, 100 μM) on germ tube formation by C. albicans GDH 2346. Germ tube formation is expressed as a percentage of that for control cells incubated in the absence of inhibitors. Results are means ± standard errors of the means of triplicate determinations. The mean ± standard error of the mean value for the controls was 72.6 ± 12 germ tube-forming cells/200 counted cells.