(436a) Deciphering the Mechanisms of Fluoroquinolone-Mediated Mutagenesis

Antimicrobial resistance continues to remain a critical global health issue. Unfortunately, there is an insufficient research and development pipeline, and more steps are urgently required to effectively implement better strategies in drug design and delivery. Bacteria need to protect their genomic material from numerous chemical mutagens in circulation to maintain genomic integrity. One common mutagen is the fluoroquinolone class of antibiotics, which are commonly used for the treatment of infectious diseases. Fluoroquinolones target DNA gyrase and topoisomerase IV enzymes during DNA synthesis, generating double-strand breaks in DNA, which activates the SOS regulatory network (1). The SOS response induces error-prone DNA repair mechanisms that can result in mutagenesis. A multitude of intricate elements that are yet mostly unknown contribute to the complexity of the mutagenic SOS response. Gaining a thorough grasp of this phenomenon could be highly beneficial in identifying new targets that can help fight against the formation of resistant pathogens.

The SOS response network comprises more than 50 genes that are expressed in the presence of DNA damage (2), and this process needs active transcription, translation, and ATP production. When we treated cells with ciprofloxacin, a fluoroquinolone antibiotic, along with metabolic inhibitors to inhibit transcription, translation, and ATP production during the recovery of Escherichia coli cells after the fluoroquinolone treatment, we were able to impair fluoroquinolone-mediated mutagenesis (3). As transcription and translation inhibition affects the downstream mechanisms of RecA, the master regulator of the SOS network, we focused on gaining further insights into these mechanisms by performing high-throughput screening of an E. coli promoter library, containing promoters of the major SOS response genes. We identified several candidates with upregulated expression; the recA gene exhibited the highest upregulation, followed by recN, polB, dinB, and sulA, among others. Deletion of certain SOS genes, either individually or in combination, resulted in an increased sensitivity towards ciprofloxacin along with a significant reduction in intracellular mutagenesis. Overall, this study highlights the potential downstream targets of RecA that can be important in understanding and controlling intracellular mutagenesis in the context of antibiotic resistance.

References

1. Hooper, D. C. (1999). Mechanisms of fluoroquinolone resistance. Drug Resistance Updates, 2(1), 38–55. https://doi.org/https://doi.org/10.1054/drup.1998.0068

2. Maslowska, K. H., Makiela-Dzbenska, K., & Fijalkowska, I. J. (2019). The SOS system: A complex and tightly regulated response to DNA damage. Environmental and molecular mutagenesis, 60(4), 368–384. https://doi.org/10.1002/em.22267

3. Sreyashi, G., & A, O. M. (2024). Exploring the links between SOS response, mutagenesis, and resistance during the recovery period. Antimicrobial Agents and Chemotherapy, 0(0), e01462-23. https://doi.org/10.1128/aac.01462-23