Abstract
Object. To determine if tetracycline, previously reported to increase the probability of developing symptomatic vaginal yeast infections, has a direct effect on Candida albicans growth or induction of virulent phenotypes. Method. In vitro, clinical isolates of yeast were cultivated with sublethal concentrations of tetracycline and yeast cell counts, hyphal formation, drug efflux pump activity, biofilm production, and hemolysin production were determined by previously reported methods. Results. Tetracycline concentrations above 150 μg/mL inhibited Candida albicans, but at submicrogram/mL, a modest growth increase during the early hours of the growth curve was observed. Tetracycline did not inhibit hyphal formation at sublethal concentrations. Hypha formation appeared augmented by exposure to tetracycline in the presence of chemically defined medium and especially in the presence of human serum. Efflux pump CDR1 was upregulated and a nonsignificant trend toward increased biofilm formation was noted. Conclusion. Tetracycline appears to have a small growth enhancing effect and may influence virulence through augmentation of hypha formation, and a modest effect on drug efflux and biofilm formation, although tetracycline did not affect hemolysin. It is not clear if the magnitude of the effect is sufficient to attribute vaginitis following tetracycline treatment to direct action of tetracycline on yeast.
Highlights
Epidemiological studies purport that the use of certain antibiotics during pregnancy increases susceptibility to vulvo-vaginal candidiasis [1, 2]
To establish whether any concentration of tetracycline altered growth of Candida albicans strains, various concentrations were tested for their effects on overnight growth; concentrations of tetracycline between 5 and 0.15 mg/mL were inhibitory toward Candida albicans with 5 mg/mL reducing hemacytometer counts to near zero and 150 μg/mL reducing counts by half compared to the control containing no tetracycline
This study focused on the possibility that growth of Candida albicans and the expression of virulence attributes may be altered by the exposure of this fungal pathogen to tetracycline
Summary
Epidemiological studies purport that the use of certain antibiotics during pregnancy increases susceptibility to vulvo-vaginal candidiasis [1, 2] This condition is generally believed to result from the suppression of a bacterial flora in the face of antibacterial drugs that fail to inhibit Candida, resulting in its overgrowth and subsequent emergence of symptoms. In 1998, Glover and Larsen [4], curious about the magnitude of the impact of antibiotics on yeast vaginitis, unexpectedly found that nonantibiotic-treated pregnant patients became symptomatic more frequently than did the patients treated with antibiotics This prompted a search in the literature for evidence of a direct effect of antibiotic treatment on yeast colonization. Tetracycline was implicated by Oriel and Waterworth [5] who indicated that 14 days of tetracycline or minocycline treatment increased vaginal Candida culture positive rate from 13% to 29%
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