How some resistant bacteria can even eat antibiotics as food

Some bacteria are capable of not just resisting antibiotics, but actively feeding on them too. Now researchers have figured out how they do this. Ten years ago, Gautam Dantas at Washington University in St Louis and his colleagues discovered that some bacteria could eat antibiotics by accident. As part of an experiment, they were growing soil bacteria in the presence of penicillin, expecting that this would stop the bacteria from growing. “But we saw exceptional growth on antibiotics,” says Dantas, whose team found that some strains were around 50 times above the threshold at which bacteria are normally classed as antibiotic-resistant, and that they were feeding on the penicillin. Many other types of soil bacteria have been found to do the same since. To find out how they do it, Dantas and his colleagues grew four of these strains under various lab conditions.

Break it down

They focussed on genes that became active when the bacteria were exposed to penicillin, and individually deleted one gene at a time to see what effect this had. This revealed that the bacteria are able to thrive on penicillin using a cocktail of different enzymes – proteins that catalyse chemical reactions. The bacteria first use an enzyme to resist the antibiotic, so that it doesn’t interfere with their cell walls and kill them when they grow and multiply. They then use a couple of enzymes to start breaking the penicillin apart, before a slew of 10 or more enzymes enable the bacteria to use the carbon in the degraded antibiotic as a food source. When genes for these enzymes were given to harmless Escherichia coli bacteria, it became able to eat antibiotics the same way. Antibiotics have been around for millions of years, so it’s not surprising that bacteria have evolved to use them as a food source, says Matthew Avison at the University of Bristol, UK. “We have to accept that if you take antibiotics from nature, there will be bacteria that can break them down,” he says Avison.

Ahead of the game

So far, no disease-causing bacteria are known to eat antibiotics in this way. But bacteria can easily swap and share genes, so this may not last for long, particularly among human pathogens that come from the soil. “They have the opportunity to acquire and use the same pathways,” says Laura McCaughey at the University of Technology, Sydney. Dantas hopes his findings will help us stay a step ahead of the game, enabling researchers to create antibiotics that can’t be broken down in this way. We may also be able to find uses for the enzymes used by the soil bacteria, using them to break down antibiotics that get out into the environment, and reducing the risk of them driving the evolution of resistance. Antibiotics from our urine are increasingly turning up in our tap water, says Jonathan Cox at Aston University, UK. “If you were to add a culture of the researchers’ modified E. coli strain into a vat of raw sewage, it [could] proliferate and break down antibiotics,” he suggests.

New Scientist, 30 April 2018 ; http://www.newscientist.com/

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