Fungicidal effects of chemical disinfectants, UV light, desiccation and heat on the amphibian chytrid Batrachochytrium dendrobatidis

Abstract

The efficacy of a number of disinfection treatments was tested on in vitro cultures of the fungus Batrachochytrium dendrobatidis, the causative agent of chytridiomycosis in amphibians. The aim was to evaluate the fungicidal effects of chemical disinfectants, sterilising ultraviolet (UV) light, heat and desiccation, using methods that were feasible for either disinfection in the field, in amphibian husbandry or in the laboratory. The chemical disinfectants tested were: sodium chloride, household bleach (active ingredient: sodium hypochlorite), potassium permanganate, formaldehyde solution, Path-X TM agricultural disinfectant (active ingredient: didecyl dimethyl ammonium chloride, DDAC), quaternary ammonium compound 128 (DDAC), Dithane, Virkon, ethanol and benzalkonium chloride. In 2 series of experiments using separate isolates of B. dendrobatidis, the fungicidal effect was evaluated for various time periods and at a range of chemical concentrations. The end point measured was death of 100% of zoospores and zoosporangia. Nearly all chemical disinfectants resulted in 100% mortality for at least one of the concentrations tested. However, concentration and time of exposure was critical for most chemicals. Exposure to 70% ethanol, 1 mg Virkon ml -1 or 1 mg benzalkonium chloride ml -1 resulted in death of all zoosporangia after 20 s. The most effective products for field use were Path-X TM and the quaternary ammonium compound 128, which can be used at dilutions containing low levels (e.g. 0.012 or 0.008%, respectively) of the active compound didecyl dimethyl ammonium chloride. Bleach, containing the active ingredient sodium hypochlorite, was effective at concentrations of 1% sodium hypochlorite and above. Cultures did not survive complete drying, which occurred after < 3 h at room temperature. B. dendrobatidis was sensitive to heating, and within 4 h at 37°C, 30 min at 47°C and 5 min at 60°C, 100% mortality occurred. UV light (at 1000 mW m -2 with a wavelength of 254 nm) was ineffective at killing B. dendrobatidis in culture. Disinfectants play a role in at least 3 situations: (1) to prevent the spread of amphibian disease in the wild by cleaning equipment that comes into contact with amphibians, such as nets and toe-clipping instruments, as well as by cleaning items that come into contact with water, such as boots; (2) in captive husbandry, as a crucial part of quarantine in cleaning equipment and enclosures before reuse, and (3) in the laboratory, to prevent contamination and to kill unwanted cultures. An ideal disinfectant would work rapidly, be safe for the human operator, have minimal impact on equipment, have a low risk of contaminating the environment, be easily available, and any residual concentration would have no effect on amphibians.Because a resistant resting spore has not been detected for Batrachochytrium dendrobatidis , this study evaluates the ability of a disinfectant to kill zoospores and zoosporangia only. MATERIALS AND METHODSThe physical techniques tested were desiccation, ultraviolet (...

Dynamics of an emerging disease drive large-scale amphibian population extinctions

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The pathogenBatrachochytrium dendrobatidisdisturbs the frog skin microbiome during a natural epidemic and experimental infection

“…To prevent researcher-mediated spread of Bd among R. sierrae populations, before conducting surveys or sampling at any field site, all field research equipment (including nets and shoes) that contact lake water or frogs was disinfected with 0.1% quaternary ammonium compound 128 solution and incubated for at least 5 min (78) or, in the case of small or sensitive equipment, disinfected with 70% ethanol.…”

Lack of Evidence for the Drought-linked Chytridiomycosis Hypothesis

“…Batrachochytrium dendrobatidis has waterborne zoospores (Longcore et al, 1999;Piotrowski et al, 2004), and cannot survive desiccation (Johnson et al, 2003), so it is unlikely that that dry weather would benefit the fungus. Indeed, bioclimatic modeling predicts that the fungus is more likely to inhabit wetter regions (Ron, 2005), and recent field studies confirm this prediction.…”