'Persister' Bacteria May Pass Along Resistance Genes

Judicious Use of Antibiotics May Not Be Enough To Defeat Bacteria That Carry On By Going Into a Dormant State

Restricting the use of antibiotics may not be enough to curb the spread of resistant bacteria: Efforts will also have to focus on preventing infections by the superbugs in the first place, according scientists at ETH Zurich. They reported in Nature about a previously unknown mechanism of antibiotic resistance spread in bacteria that inhabit the gut.

The team discovered the mechanism in so-called persisters—bacteria that can survive treatment with antibiotics by going into a dormant state. "If you want to control the spread of resistance genes," says co-senior study author Médéric Diard, "you have to start with the resistant microorganisms themselves and prevent these from spreading through, say, more effective hygiene measures or vaccinations."

Resistance genes empower bacteria with various means of defeating antibiotics: ejecting the antibiotic from the cell, keeping the drug from getting into the cell in first place, neutralizing  it with enzymes—or some combination of three.

The Swiss researchers’ findings suggest that restricting the use of antibiotics may not be enough to fight resistance because, thanks to persisters, it can spread without antibiotic use. Persisters can wind down their metabolism to such an extent that they are barely still alive.

Salmonella, for instance, can become a persister when it invades body tissues from the intestines. This bacterium can lie dormant and escape detection for many months. When conditions become favorable, the germ can wake up and trigger infection. Even if the microbes do not cause an full-on infection, they can still pose a threat, according to the new findings.

The researchers found that Salmonella has the ability not only to persist but also to carry resistance genes in plasmids.

In experiments in mice, the team showed that when the plasmid-carrying Salmonella persisters emerge from dormancy, they can readily pass on their resistance genes not only to members of their own species but also to those of other species of bacteria, including Escherichia coli in the gut flora.

The researchers point out that the transfer of the resistance genes does not depend on the presence of antibiotics. "Restricting the use of antibiotics is important and [...] indeed the right thing to do,” they note, “but this measure alone is not sufficient to prevent the spread of resistance."

Source: Medical News Today, Sept. 9