Timing is key for bacteria surviving antibiotics
For bacteria facing a dose of antibiotics, timing might be the key to evading destruction. In a series of experiments, Princeton researchers found that cells that repaired DNA damaged by antibiotics before resuming growth had a much better chance of surviving treatment.
When antibiotics hit a population of bacteria, often a small fraction of “persister” cells survive to pose a threat of recurrent infection. Unlike bacteria with genetic resistance to antibiotics, evidence suggests that persisters stay alive in part by stalling cellular processes targeted by the drugs.
In a new study, Princeton researchers examined a class of antibiotics that target bacterial DNA. In bacterial populations, some cells repair damaged DNA before resuming growth, and others resume growth before making repairs. The researchers found that those that make repairs before resuming growth generally are the ones that survive as persisters. The research advances a long-term goal to make antibiotic treatment more effective.
In results published June 18 in the Proceedings of the National Academy of Sciences, Wendy Mok, a post-doctoral researcher, and Mark Brynildsen, an associate professor of chemical and biological engineering, analyzed the responses of E. coli bacteria to treatment with ofloxacin, an antibiotic that causes DNA damage by blocking enzymes needed for DNA replication and RNA transcription. Their work built on previous results from Brynildsen’s lab, which revealed that persisters to ofloxacin required DNA repair machinery to survive.
To test this hypothesis, Mok and Brynildsen used a strain of E. coli bacteria that had been genetically engineered to allow researchers to control the cells’ growth. The researchers used the bacteria to create a uniform population of cells with stalled growth that could tolerate the ofloxacin antibiotic.
By controlling the activity of a key DNA repair protein, RecA, the researchers tested the effect of further delaying DNA repair until after the resumption of DNA synthesis. This led to a sevenfold decrease in survival compared to cells that continuously produced RecA, demonstrating that persistence to ofloxacin depends on repairing DNA damage before synthesizing the new DNA necessary for growth.