Researchers have uncovered the first steps driving antibiotic resistance

Antibiotic resistance poses a global health threat. In 2019 alone, 1.3 million deaths were attributed to antibiotic-resistant bacterial infections worldwide. Seeking to contribute to solving this growing problem, researchers at Baylor College of Medicine have been studying the process that drives antibiotic resistance at the molecular level.

They write in the magazine molecular cell The critical and surprising first steps promoting resistance to ciprofloxacin, or Cipro for short, one of the most commonly used antibiotics. The findings point to potential strategies that can prevent bacteria from developing resistance, increasing the effectiveness of new and old antibiotics.

Said co-author Dr. Susan M Rosenberg Chair, Ben F. Love is a professor of cancer research and professor of molecular and human genetics, biochemistry, molecular biology, virology, and microbiology at Baylor. She is also the Program Lead at the Dan L. Duncan Comprehensive Cancer Center at Baylor (DLDCCC).

“We discovered that cipro triggers cellular stress responses that promote mutations. This phenomenon, known as stress-induced mutagenesis, generates mutant bacteria, some of which are resistant to cipro. Cipro-resistant mutants continue to grow, sustaining infections they can no longer handle. them with Cipro.”

Cipro induces breaks in the DNA molecule, which accumulate within bacteria and thus trigger a DNA damage response to repair the breaks. Rosenberg’s lab discoveries of the steps involved in stress-induced mutations revealed that two stress responses are necessary: ​​the general stress response and the DNA damage response.

Some of the final steps of the process that lead to increased mutagenesis were previously revealed in Rosenberg and colleagues’ lab. In this study, the researchers explored the molecular mechanisms of the first steps between an antibiotic causing DNA refraction and the transformation of bacteria upon a DNA damage response.

“We were surprised to find an unexpected molecule involved in modulating DNA repair,” said first author Dr. Yin Zhai, a postdoctoral fellow in the Rosenberg lab. “Normally, cells regulate their activities by producing specific proteins that mediate the desired function. But in this case, the first step to triggering a DNA repair response wasn’t about activating specific genes that produce specific proteins.”

Instead, the first step consists of inactivating an already existing protein, RNA polymerase. RNA polymerase is key to protein synthesis. This enzyme binds to DNA and transcribes the DNA-encoded instructions into an RNA sequence, which is then translated into a protein.

“We discovered that RNA polymerase also plays a key role in regulating DNA repair,” Chai said. “A small molecule called the nucleotide ppGpp, which is present in bacteria exposed to a stressful environment, binds to RNA polymerase through two separate sites necessary to trigger the repair response and the general stress response. Interference with one of these sites stops DNA repair specifically in the DNA sequence it occupies. RNA polymerase”.

“ppGpp binds to DNA-binding RNA polymerase, telling it to stop and retract along the DNA to repair it,” said co-author Dr. Christoph Hermann, Professor of Molecular and Human Genetics, Molecular Virology and Microbiology and DLDCCCC member. . Herrmann’s lab found the repair-RNA-polymerase connection previously, reported in nature.

Rosenberg’s lab discovered that DNA repair can be an error-prone process. As the repair of broken DNA strands progresses, errors occur that alter the original DNA sequence producing mutations. Some of these mutations will confer resistance to Cipro bacteria. “Interestingly, the mutations also induce resistance to two other antibiotics that bacteria have not seen before,” Zhai said.

“We are excited about these results,” said Rosenberg. “It opens up new opportunities for designing strategies that will interfere with the development of antibiotic resistance and help turn the tide on this global health threat. Also, Cipro breaks bacterial DNA in the same way that the anticancer drug etoposide breaks human DNA in tumors. We hope.” This addition could lead to new tools for combating cancer chemotherapy resistance.”