In a paper in Microbiology Spectrum, biologists analyzed the venom of two species of spiders and five of snakes, including the western diamond rattlesnake and the black-necked cobra. All seven venoms tested contained bacterial DNA. When the researchers cultured the bacteria and analyzed the DNA, they found that some of the bacteria could survive and even multiply in venom.

“This is extraordinary because venom is like a cocktail of antibiotics, and it is so thick with them, you would have thought the bacteria would not stand a chance,” said Sterghios Moschos, a biology professor at Northumbria University in England, in a news release.

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The work challenges another assumption: that people who get snakebite-related infections caught them from their wound. Instead, the paper suggests that the bacteria comes from the venom itself.

The researchers suggest that clinicians change the way they deal with wound management in those who have been bitten by venomous snakes or spiders, and they say the mutated bacteria may present an especial risk to people who are immunocompromised.

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Snakebites are common in developing nations where malnutrition can lower people’s immune defenses to infection. The World Health Organization estimates that up to 2.7 million people are bitten by a venomous snake each year, and that up to 138,000 die of snake bites. Amputations, tissue damage and disability can also occur — and poor, rural communities experience the most envenomings.

In recent years, biologists have challenged another myth: that urine is sterile. Researchers from Loyola University have even identified a bladder microbiome — even more proof of the microbes’ marvelously vexing ability to survive.