“Study: Low-level antibiotics can produce high-level resistance”

“A new study by scientists in Sweden indicates that bacteria exposed to small concentrations of antibiotics over time can become highly resistant, a finding the authors say provides an example of how low levels of antibiotics present in many environments may potentially contribute to antibiotic resistance.

In the study, published this week in Nature Communications, researchers from Uppsala University demonstrated that Salmonella exposed repeatedly to an amount of streptomycin that was not strong enough to kill the bacteria or inhibit growth still evolved high-level resistance. The resistance was caused by genetic mutations that haven’t been typically associated with antibiotic resistance and were different from those that develop when the bacteria is exposed to lethal amounts of the drug.

“These results demonstrate how the strength of the selective pressure influences evolutionary trajectories and that even weak selective pressures can cause evolution of high-level resistance,” the authors write.”

Source: CIDRAP