Reviewed by Kate Anderton, B.Sc. (Editor) Feb 4 2020
Can staph microbes lead to cancer?
Microbes are known to affect digestion, mood and overall health, and now Princeton researchers have shown that a shift in the microbiome is linked to cancer -- at least in a threatened subspecies of foxes found only on one island off the California coast.
Their research suggests a several-step process: First, the cat-sized Santa Catalina foxes become infested with ear mites, which change the foxes' microbiome and allow a staph infection to take hold. As Staphylococcus pseudintermedius runs rampant, the antibiotic-resistant infection leads to chronic inflammation of the foxes' ears. In that environment of inflamed tissue, tumors can flourish. The researchers detailed their findings in the journal Molecular Ecology .
"We were really excited to find such clear results," said Alexandra DeCandia, the first author on the paper and a graduate student in the lab of Bridgett vonHoldt, an associate professor of ecology and evolutionary biology at Princeton University. "Everything we found -- reduced species diversity, shifts in community composition, overabundance of potentially pathogenic species -- fit within our expectations."
The project started during conservation efforts on Santa Catalina Island, when researchers noticed that roughly half of the adult foxes had tumors growing in their ears. That's one of the highest tumor rates ever observed in wildlife, prompting immediate follow-up study.
Early work demonstrated a link between ear mite infection and tumor growth. Most researchers theorized that ear mites led to chronic inflammation, ultimately sparking the growth of tumors. DeCandia and vonHoldt's team wanted to know whether the microbiome also played a role in this system.
That focus on diversity within the microbiome makes their work an excellent example of where the field is going to move in the future. We've only recently learned how important the microbiome is to an individual's health -- whether it's an animal or a human. Previously, scientists only examined part of the picture. They certainly weren't looking at microbiomes -- they didn't even have tools to do it. ... By examining that, we've come to understand that a lack of diversity in that microbial community, combined with the genetics of the foxes, best helps us understand not only the threat of this particular disease but other diseases as well. This really is a new paradigm for understanding threats to endangered species." George Amato, director of conservation genomics at the American Museum of Natural History
The threatened Santa Catalina foxes are one of six subspecies of Channel Island foxes (Urocyon littoralis) that live on six of the eight Channel Islands off the coast of southern California. Several of the subspecies, including those on Santa Catalina (U. littoralis catalinae), have made impressive rebounds from the brink of extinction -- with the result that they are all incredibly similar genetically, nearly clones of each other.
The foxes' almost total lack of genetic diversity makes them fascinating research subjects, said DeCandia.
"We typically view genetic diversity as a good and necessary thing," she said. "It keeps organisms healthy -- think of the negative health effects associated with inbreeding -- and helps populations survive unexpected changes to their environment. But despite having almost no genetic variation, these foxes exhibit very few signs of poor health or inbreeding depression. That leads us to wonder whether other forms of diversity -- such as their resident organisms -- become important players in health and immunity. That's why we focused our study on the microbiome and disease in these foxes." Related Stories
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