Ford et al., Featured in the Antimicrobial Research Review

Genes that impart antimicrobial resistance are all but certain to take up permanent residence in a bacterium. Researchers at the University of North Carolina at Charlotte report that, once antibiotic-resistance genes appear, they persist in Escherichia coli genomes even when they are no longer needed. This tendency, which the researchers call genetic capitalism, compounds the difficulty of wiping out drug-resistant bacterial strains.

According to a principle called stabilizing selection, many genes drop out of the bacterial genome when they no longer provide survival benefits. But after sequencing the genomes of more than 29,000 strains of E. coli dating from 1884 to 2018, biomathematician Colby Ford and his team concluded that antibiotic-resistance genes were not dropping out of the bacterial genome as much as expected. After antibiotic use became widespread around the middle of the twentieth century, the researchers note, E. coli would have had to hoard antibiotic-resistance genes to survive.

The few resistance genes that did fade were ones that demanded a high level of energy consumption, such as those coding for processes that physically push the antibiotic out of the bacterial cell. The research suggests, therefore, that taking certain antibiotics out of circulation for an extended period to reduce resistance, before gradually reintroducing them — a strategy known as antibiotic cycling — is likely to be more effective for drugs, such as tetracycline, that require bacteria to spend considerable energy resisting.

Cladistics https://doi.org/d9qt (2020)