Coordinated topoisomerase function shapes the fluoroquinolone response of Chlamydia trachomatis

ABSTRACT DNA supercoiling is essential for the developmental cycle of Chlamydia trachomatis , yet its role in shaping antibiotic responses remains poorly understood. We investigated how the fluoroquinolone moxifloxacin (Mox), a potent DNA gyrase inhibitor, affects C. trachomatis by examining developmental progression, DNA replication, topoisomerase expression, and transcriptional response in select genes. Early Mox exposure completely halted bacterial growth, whereas treatment during mid-developmental cycle produced small inclusions with enlarged bacterial forms and abolished formation of infectious progeny. These outcomes coincided with inhibition of DNA replication, apparent loss of detectable DNA gyrase, and repression of ompA and omcB transcription, while the expression of the groESL1 operon was preserved or elevated. Mox also elicited the downregulation of topoisomerase I (TopA), consistent with compensatory rebalancing of DNA supercoiling. Together, these data demonstrate that Mox exerts differential effects across the developmental stages and that disrupted gyrase-TopA coordination drives chlamydial developmental arrest and a noncanonical, DNA replication-limited persistent phenotype IMPORTANCE C. trachomatis , a clinically significant obligate intracellular bacterial pathogen, can persist under antimicrobial pressure, complicating treatment strategy. This study links supercoiling homeostasis to fluoroquinolone tolerance, providing mechanistic insights into chlamydial responses to topological stress and identifying potential targets to overcome noncanonical persist state.