Interplay between Topoisomerase II Gene Evolution and Selective Pressure: The Camps lab’s research on topoisomerase II genes, which are targeted by fluoroquinolone antibiotics, has uncovered an intriguing evolutionary pathway. We have identified an antagonistic relationship between this pathway and mutations in the Quinolone Resistance Determining Regions (QRDR), which confer fluoroquinolone resistance. Additionally, our investigation has revealed that the evolution of this pathway is primarily driven by the selective pressure exerted by the chromosomal toxin CcdB. This breakthrough has significant translational implications, as strains carrying the ccdAB gene cassette are less prone to developing resistance to fluoroquinolones.