Molecular Mechanisms of Fluoroquinolone Resistance in Escherichia coli from Urinary Tract Infections in Tertiary Hospitals Across South South Nigeria

Fluoroquinolone resistance in urinary tract infection (UTI)-associated Escherichia coli has become clinically problematic in Nigeria, yet the molecular mechanisms underlying this resistance in South South hospital isolates are not well characterised. This study investigates the molecular mechanisms of fluoroquinolone resistance in E. coli isolated from UTI specimens at tertiary hospitals in Rivers, Bayelsa, and Akwa Ibom States. Urine culture specimens from 300 UTI patients were processed by standard methods, and E. coli isolates with ciprofloxacin MIC above 4 mg/L were selected for molecular analysis. PCR and sequencing detected chromosomal mutations in gyrA and parC genes, while plasmid-mediated quinolone resistance (PMQR) genes including qnrA, qnrB, qnrS, aac(6)-ib-cr, and qepA were characterised by multiplex PCR. Ciprofloxacin resistance was confirmed in 44 percent of E. coli isolates. gyrA mutations (S83L and D87N) were the dominant resistance mechanism, present in 78 percent of resistant isolates. PMQR genes were identified in 41 percent of resistant isolates, most commonly qnrB (26 percent) and aac(6)-ib-cr (19 percent). Co-occurrence of chromosomal and plasmid mechanisms was observed in 22 percent of isolates. Conjugation experiments confirmed horizontal PMQR gene transfer. The study identifies a multimechanistic fluoroquinolone resistance landscape in South South Nigerian UTI E. coli, with plasmid-mediated mechanisms facilitating inter-isolate spread. Keywords: fluoroquinolone resistance, Escherichia coli, UTI, PMQR, South South Nigeria