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For bacteria facing a dose of antibiotics, timing might be the key to escaping destruction. In a series of experiments, Princeton researchers found that cells that repaired DNA damaged by antibiotics before resuming their growth were far more likely to survive.
When antibiotics affect a bacterial population, a small fraction of "persistent" cells survive. pose a threat of recurrent infection. In contrast to bacteria with genetic resistance to antibiotics, the evidence suggests that persists remain in part by delaying drug-mediated cellular processes.
In a new study, Princeton researchers examined a class of antibiotics targeting bacterial DNA. In bacterial populations, some cells repair the damaged DNA before resuming growth, and others resume their growth before making repairs. The researchers found that those who make repairs before resuming growth are usually those who survive as persist. Research advances a long-term goal to make antibiotic treatment more effective.
In the results published June 18 in the Proceedings of the National Academy of Sciences, Wendy Mok, a postdoctoral researcher, and Mark Brynildsen, associate professor of chemical and biological engineering, analyzed the responses of bacteria E. coli to treatment with ofloxacin, an antibiotic that causes damage to DNA by blocking the enzymes necessary for DNA replication and RNA transcription. Their work is based on previous results from the Brynildsen laboratory, which revealed that persistent bacteria to ofloxacin required DNA repair to survive.
"But that does not necessarily guarantee that they survive," said Mok. "We hypothesized that the timing of DNA repair and the resumption of growth-related activities such as DNA synthesis could impact survival of persis after treatment."
To test this hypothesis, Mok and Brynildsen used an E. coli bacterium that had been genetically engineered to allow researchers to control cell growth. The researchers used the bacteria to create a uniform population of cells with stagnant growth that could tolerate the antibiotic ofloxacin.
These non-growth cells, they discovered, suffered similar DNA damage to cells grown with ofloxacin. However, the non-cultured cells delayed the resumption of synthesis and repair of the DNA after the treatment.
By controlling the activity of a key protein repair DNA, RecA, the researchers tested the effect of delaying the repair of DNA. synthesis. This led to a seven-fold decrease in survival compared to cells that continuously produced RecA, demonstrating that persistence to ofloxacin depended on repairing DNA damage before synthesizing the new DNA needed to the growth.
Mok and Brynildsen then examined the persistence of low-nutrient environments to stall their growth, simulating a condition that bacteria frequently encounter in an infected host. Indeed, following treatment with ofloxacin, if the cells were deprived of carbon sources for at least three hours, they observed an almost complete tolerance to the antibiotic. This tolerance depended on effective processes of DNA repair. They also observed an increase in the persistence of ofloxacin with nutrient deprivation after treatment of cultured cells in biofilms, groups of bacteria that adhere to surfaces and are involved in the majority of hospital bacterial infections.
Jan Michiels, a professor of microbiology at the University of Louvain-VIB in Belgium, said the study used "an elegant model system" to probe the underlying mechanisms of persistence. Michiels, who did not participate in the research, said that it represented "a historical discovery providing new fundamental ideas about how persistent cells avoid death."
L & # 39; Ofloxacin and other similar antibiotics are on the Model List of Essential Medicines of the World Health Organization. a catalog of the most important drugs to meet the needs of health care. Curbing bacterial persistence may be a promising way to make these therapies more effective against urinary tract infections, staphylococcal infections and other bacterial diseases.
"Nutrient deprivation is a stress that bacteria can regularly encounter at an infection site." Our results suggest that in the period after antibiotic treatment, we may consider targeting some of these repair processes of DNA, and see if this can improve treatment outcomes. "A counterintuitive approach might be to accelerate bacterial growth after antibiotic therapy, thus condemning cells to go beyond their repair mechanisms and to die. However, the researchers added that other approaches would probably be better than to promote the growth of a pathogen in a patient.
The Brynildsen group and other researchers are interested in finding drug compounds that may interfere with the repair of bacterial DNA the relationship between antibiotic tolerance and resistance Genetics.
Support for this research was provided in part by the Army Research Office, the Charles H. Revson Foundation, and the founding funds of Princeton University
Source: Princeton University
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