Abstract
Host-associated microbes form an important component of immunity that protect against infection by pathogens. Treating wild individuals with these protective microbes, known as probiotics, can reduce rates of infection and disease in both wild and captive settings. However, the utility of probiotics for tackling wildlife disease requires that they offer consistent protection across the broad genomic variation of the pathogen that hosts can encounter in natural settings. Here we develop multi-isolate probiotic consortia with the aim of effecting broad-spectrum inhibition of growth of the lethal amphibian pathogen Batrachochytrium dendrobatidis (Bd) when tested against nine Bd isolates from two distinct lineages. Though we achieved strong growth inhibition between 70 and 100% for seven Bd isolates, two isolates appeared consistently resistant to inhibition, irrespective of probiotic strategy employed. We found no evidence that genomic relatedness of the chytrid predicted similarity of inhibition scores, nor that increasing the genetic diversity of the bacterial consortia could offer stronger inhibition of pathogen growth, even for the two resistant isolates. Our findings have important consequences for the application of probiotics to mitigate wildlife diseases in the face of extensive pathogen genomic variation.
Highlights
Emerging infectious diseases pose a significant threat to human and wildlife health, and are responsible for driving declines in biodiversity around the globe (Jones et al, 2008; Tompkins et al, 2015; Scheele et al, 2019)
Considering only the random effects, variance component analysis indicated that Batrachochytrium dendrobatidis (Bd) isolate explained slightly more variance than bacterial genus [Bd mean = 28.4% (16.1–40.7); bacterial genus mean = 21.1% (7.9–36.3)]
We found no evidence that more closely related Bd isolates had more similar inhibition profiles across the panel of probiotics tested (Mantel test p = 0.6; Figures 3A,B), the two Bd isolates most resistant to inhibition were relatively genetically similar
Summary
Emerging infectious diseases pose a significant threat to human and wildlife health, and are responsible for driving declines in biodiversity around the globe (Jones et al, 2008; Tompkins et al, 2015; Scheele et al, 2019). The last few decades alone have witnessed the emergence and spread of multiple viral and fungal pathogens capable of infecting a broad range of host species, and developing strategies to mitigate the loss of wildlife species caused by disease is a key priority. Probiotics comprising single bacterial species appear unlikely to be provide a “silver bullet” capable of inhibition across the broad spectrum of pathogen variants observed in natural systems. This issue is exacerbated by the propensity of pathogen genotypes to spread rapidly around the globe, often as a result of human activity (O’Hanlon et al, 2018), exposing susceptible hosts to multiple and novel threats (Greenspan et al, 2018; Longo et al, 2019). Designing novel probiotic strategies that are effective against the full panorama of pathogen genotypes is necessary in order to effect meaningful change in the rates of infection caused by emerging infectious diseases
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