Antibiotics can help some bacteria survive for longer and protect them from death, research has suggested.
The drugs have traditionally been used as a blanket medication for infections, as it is believed they kill bacteria or stop them from growing.
However, research has shown that the drugs can actually protect or even benefit bacteria, with some cultures not growing in the laboratory until they were treated with antibiotics.
Antibiotic resistance has stopped some drugs from working as bacteria change in response to the use of these medicines.
This means that untreatable infections could be the biggest global cause of death by 2050, experts say.
In the research funded by the Engineering and Physical Sciences Research Council and published in the Proceedings of the National Academy of Sciences journal, the team found that certain antibiotics can alleviate stress and help prevent the decline of bacterial populations when they are dying out.
This means more bacteria survive for longer compared to untreated populations.
“The study began when we realised that, surprisingly, some bacterial strains didn’t grow in the lab until we treated them with antibiotics,” said lead author Robert Beardmore, from the University of Exeter.
“As a result, this is the first evidence that antibiotics can promote bacterial survival.
“To tackle antibiotic resistance worldwide, we need to understand far more about the impact of these drugs on the balance of bacterial ecosystems, like those in the gut microflora, or in rivers that are exposed to antibiotics.
“Our research is evidence of unseen side effects – we just don’t know how drugs are changing the balance of bacterial populations in those contexts.”
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Bacteria undergo periods of rapid growth, punctuated by periods where growth stops because nutrients are scarce, so the bacteria die off.
So far, little is known about how antibiotics mediate populations during those periods.
The researchers examined E coli in lab experiments.
They found that antibiotics that attacked ribosomes – factories that help cells make protein from DNA – slowed bacteria down as they were growing.
But they also stopped them from dying, meaning the bacteria survived for longer overall, the study suggests.