In vitro sensitivity of the amphibian pathogen Batrachochytrium dendrobatidis to antifungal therapeutics

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Highlights

  • We report the sensitivity of Batrachochytrium dendrobatidis to six antimicrobials.

  • Voriconazole, itraconazole, and terbinafine had potent inhibitory effects.

  • Terbinafine and amphotericin B exposure killed zoospores rapidly.

  • The reported MIC and killing concentrations are useful for design of dosage regimens.

Abstract

Chytridiomycosis, a skin disease caused by Batrachochytrium dendrobatidis, has caused amphibian declines worldwide. Amphibians can be treated by percutaneous application of antimicrobials, but knowledge of in vitro susceptibility is lacking. Using a modified broth microdilution method, we describe the in vitro sensitivity of two Australian isolates of B. dendrobatidis to six antimicrobial agents. Growth inhibition was observed, by measurement of optical density, with all agents. Minimum inhibitory concentrations (µg/ml; isolate 1/2) were – voriconazole 0.016/0.008; itraconazole 0.032/0.016; terbinafine 0.063/0.063; fluconazole 0.31/0.31; chloramphenicol 12.5/12.5; amphotericin B 12.5/6.25. Killing effects on zoospores were assessed by observing motility. Amphotericin B and terbinafine killed zoospores within 5 and 30 min depending on concentration, but other antimicrobials were not effective at the highest concentrations tested (100 µg/ml). This knowledge will help in drug selection and treatment optimization. As terbinafine was potent and has rapid effects, study of its pharmacokinetics, safety and efficacy is recommended.

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Acknowledgments

The authors acknowledge R. Webb for laboratory assistance, J. Voyles, G. Marantelli and M. West for involvement in collecting isolates, B. Glass, S. Robertson and S. Bell for advice on study design and interpretation and I. Beveridge for his support. Financial support was provided by the Australian Research Council and James Cook University.

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This manuscript was presented in preliminary form at the Unusual and Exotic pet veterinarians (Australian Veterinary Association) annual conference, Melbourne, Australia, September 2012.

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