New research shows – surprisingly – that bacteria can even be found in the venom of snakes. And the same goes for spider venom.

At first glance, the venom of snakes and spiders doesn’t seem like a very hospitable place for microbes. Especially not when you consider that the venom is rich in antimicrobial substances. No wonder scientists have assumed for decades that snake and spider venom is sterile. But that assumption can be changed, researchers are now writing in the magazine Microbiology Spectrum† In their study they show that bacteria can survive in the venom and/or the venom glands of spiders and snakes. And all thanks to mutations that ensure that the bacteria are not killed by that poison.

The research

The researchers examined the venom of five snakes: the common puff adder, the black-necked cobra, the injured lance-point snake, and the Texas rattlesnake and the taipan. They also examined the venom of two spiders: the Indian tree tarantula and Lasiodora parahybana (a black tarantula from Brazil). “We found that all of the venomous snakes and spiders we tested had bacterial DNA in their venom,” said researcher Sterghios Moschos.

Remarkable

The fact that the bacteria can withstand the venom of the spiders and snakes is due to mutations, according to the research by Moschos and colleagues. “They have mutated to withstand the poison. It’s remarkable because the venom is actually a cocktail of antibiotics (…) and you’d think the bacteria don’t stand a chance.” But that is not the case. Twice the bacteria have managed to adapt – both among snakes and spiders – to survive.

Experiment

The researchers deduced this not only from the presence of bacterial DNA in the venom, but also from experiments. They worked with the bacteria Enterococcus faecalis† This bacterium occurs naturally in the human gut, but was also found in the venom of the black-necked cobra during the study. The researchers determined the found in the poison E. faecalis exposed to the venom of the black-necked cobra and did the same to a hospital-isolated ‘classic’ E. faecalis† “The bacteria isolated in the hospital did not tolerate the poison at all, but the bacteria we isolated continued to grow happily in the highest concentrations of poison we could make,” says Moschos.

mutate

But how do the bacteria become resistant to poison? The researchers do have ideas about that. “Snakes in captivity are often fed weekly and can fast for months in a row (and therefore do not release venom for months, ed.) and large spiders are usually fed monthly. Wild animals can also go into a kind of hibernation for months, during which they do not release any poison,” they write in their study. Together, those conditions give the microbes a chance to colonize the venom. They probably start in a place where the venom concentration is lower (for example the mouth) and gradually climb – while mutating – to locations where the venom concentration is higher (for example in the venom glands).

Explanation for previous mysterious findings

The research explains a lot. Because bacteria like Enterococcus faecalis are remarkably often found in wounds caused by bites from venomous snakes. Because it was previously assumed that the venom was sterile, it was assumed that the bacteria do not live in the venom, but in the mouths of snakes and ended up there through the excrement of eaten prey. That seemed logical, until it was recently discovered that snakes don’t actually have a solid oral microbiome and there is no link between the bacteria found in their mouths and the bacteria that live in the gut of their prey. In addition, studies showed that more bacteria lived in the mouths of venomous snakes than in the mouths of non-venomous snakes, which is strange if you assume that the venom kills all bacteria.

Therapy

With the new research – which shows that the venom of snakes and spiders is not sterile – many pieces of the puzzle are falling into place. In addition, the study may also have implications for the treatment of, for example, snake bites. For example, the researchers point out that many people contract an infection after being bitten by a venomous snake, which is often caused by the aforementioned E. faecalis† Until recently, it was thought that the infection was the result of the open wound, but research suggests that it is the snake that already gives the bacteria as a gift – directly with the administration of the venom. In treating such wounds, therefore, the focus should not only be on fighting extreme tissue damage and necrosis, but measures should also be taken as soon as possible to prevent infection of the wound, the researchers believe.

Finally, the research could also help in the fight against a completely different problem: multi-resistant bacteria. There are more and more (disease-causing) microbes that can no longer or hardly be treated with the existing antibiotics, and as a result, diseases that could previously be easily treated – such as gonorrhea or tuberculosis, for example – are becoming untreatable again. Hundreds of thousands of people already die every year because the bacteria that make them sick do not respond to antibiotics. And it is expected that – if nothing changes – 10 million people will die every year by 2050 because the antibiotics no longer offer any solace. To avert that doomsday scenario, there is a strong search for alternative treatments for bacterial infections. But research into the way in which bacteria become resistant and how we can put a stop to this is also important. And the poison-resistant bacteria that scientists have now identified could also come in handy, says researcher Steve Trim. “By investigating the mechanisms these bacteria use to survive, we can find new ways to fight multidrug resistance.” In addition, we may also be able to look for solutions in the poison itself. For example, antimicrobial peptides in that venom – with some adjustments – may in the future be used to fight bacteria that are no longer impressed by antibiotics.