A new antibiotic weakness--drugs themselves help bacteria survive

Antibiotic treatment is often life-saving, but new evidence shows that the medications sometimes work against themselves.

Antibiotic treatment is often life-saving, but new evidence shows that the medications sometimes work against themselves. Researchers reporting in Cell Host & Microbe explain how the drugs can both protect infectious bacteria by altering the natural combination of chemicals produced by the body as well as by compromising immune cells from defending against infections. The finding comes from a team led by James Collins of Massachusetts Institute of Technology (MIT). They infected mice with Escherichia coli, giving antibiotics to some and withholding them from others. Those that received antibiotic had higher levels of metabolites—chemical compounds that bacteria can use to thrive—at the infection site compared with both infected mice that were not treated and healthy controls. Moreover, when metabolites were introduced to E. coli grown in lab plates, higher concentrations of antibiotic were needed to kill the bacteria. The same effect was observed in uninfected mice, suggesting that chemical changes were triggered by the animals' own cells rather than by bacterial cells. Additionally, mouse immune cells known as macrophages used less oxygen—which is needed to kill bacteria—when exposed to antibiotics. Treated macrophages were then infected with E. coli, with investigators discovering that they engulfed and destroyed fewer bacteria than macrophages that had not been exposed to antibiotics. Noting that some compounds—like streptomycin—slow down instead of accelerate the process of bacterial metabolism, thus weakening the potency of the antibiotics, investigators emphasize that the magnitude of the effect likely depends on the type of infection as well as the type of drugs used to treat it. Collins believes these findings may inform new ways to administer antibiotics in tandem with other substances that either minimize these changes or reverse them, making the drugs more effective.