Towards a Better Understanding of the Use of Probiotics for Preventing Chytridiomycosis in Panamanian Golden Frogs

Abstract

Populations of native Panamanian golden frogs (Atelopus zeteki) have collapsed due to a recent chytridiomycosis epidemic. Reintroduction efforts from captive assurance colonies are unlikely to be successful without the development of methods to control chytridiomycosis in the wild. In an effort to develop a protective treatment regimen, we treated golden frogs with Janthinobacterium lividum, a skin bacterium that has been used to experimentally prevent chytridiomycosis in North American amphibians. Although J. lividum appeared to colonize A. zeteki skin temporarily, it did not prevent or delay mortality in A. zeteki exposed to Batrachochytrium dendrobatidis, the causative agent of chytridiomycosis. After introduction of J. lividum, average bacterial cell counts reached a peak of 1.7 9 10 6 cells per frog *2 weeks after treatment but declined steadily after that. When J. lividum numbers declined to *2.8 9 10 5 cells per frog, B. dendrobatidis infection intensity increased to greater than 13,000 zoospore equivalents per frog. At this point, frogs began to die of chytridiomycosis. Future research will concentrate on isolating and testing antifungal bacterial species from Panama that may be more compatible with Atelopus skin.

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

“…Furthermore, expression of phenotypic traits of a given species varies with ecological contexts, such as the single-strain vs. whole-community context, culture media vs. amphibian host, or laboratory vs. field. This diversity and context dependence may help explain why augmentation with Janthinobacterium isolates has been found to increase amphibian resistance to Bd infection in some contexts (42,57) but failed to protect amphibians in another study (65).…”

Composition of symbiotic bacteria predicts survival in Panamanian golden frogs infected with a lethal fungus

“…We placed frogs in individual plastic enclosures and followed standard husbandry protocols throughout the experiment as in Becker et al [25]. Prior to any treatment, frogs underwent a two-week acclimation and observation period.…”

“…Janthinobacterium lividum is a bacterium commonly found on the skin of North American amphibians [13,23,24] and has been effective as a probiotic treatment to prevent chytridiomycosis in two North American amphibian species [9,11]. Unfortunately, probiotic therapy with J. lividum did not prevent chytridiomycosis in captive A. zeteki, as it failed to persist on the skin of experimental frogs possibly owing to host defences or competition from other resident microbes [25].…”

Interactions between amphibian skin sloughing and a cutaneous fungal disease: infection progression, immune defence, and phylogenetic patterns

“…Given the potential importance of symbiotic cutaneous bacteria in innate immune defence against Bd infection (Harris et al 2009) Understanding that these species likely slough infrequently may help pinpoint when to best bioaugment their skin with beneficial anti-Bd bacteria (Becker et al 2011, Becker et al 2015, as addition of the bacteria immediately after sloughing may allow for colonisation when resident bacterial populations are low ).…”

“…AMP activity against Bd zoospores in the laboratory has been shown to correlate with susceptibility to Bd infection in some species (Woodhams et al 2007a), but not others (Rollins-Smith et al 2006), indicating that AMPs may act differently on the amphibian host than in culture . Skin mucus may also contain metabolic products produced by symbiotic bacteria, which have been shown to be species specific even among sympatric species (McKenzie et al 2011), and variable in their efficacy to prevent Bd infection (Harris et al 2009;Becker et al 2011;Flechas et al 2012b). Collectively, these skin defence components of the mucus have been termed the 'mucosome' (Woodhams et al 2014).…”