Enrichment of the high-risk ST131 clone among ciprofloxacin-resistant Escherichia coli in a single-center cohort from Turkey: a molecular surveillance study.

Background Fluoroquinolone resistance in Escherichia coli is increasingly associated with the dissemination of high-risk lineages such as ST131. However, data integrating resistance phenotypes with molecular characteristics remain limited in local clinical settings. This study aimed to describe the distribution of ST131 and associated resistance determinants in a single-center cohort.Methods We analyzed 90 non-duplicate clinical E. coli isolates collected at a tertiary-care hospital in Turkey. Fluoroquinolone resistance was assessed using ciprofloxacin and pefloxacin. Molecular assays targeted phylogenetic groups, ST131 (including H30-Rx), ESBL genes (blaCTX-M with group assignment), plasmid-mediated quinolone resistance (PMQR) markers, and selected virulence genes. ERIC-PCR was used for genotyping and clustering. Comparative analyses were performed between ciprofloxacin-resistant and -susceptible isolates using appropriate categorical and non-parametric tests.Results Ciprofloxacin resistance was detected in 35/90 isolates (38.9%). Overall, presumptive ST131 (PCR-defined) was identified in 10/90 isolates (11.1%) and was strongly enriched among ciprofloxacin-resistant isolates (25.7% vs. 1.8%, p < 0.001); H30-Rx was also more frequent in ciprofloxacin-resistant isolates (14.3% vs. 1.8%, p = 0.031). CTX-M was detected in 31/90 isolates (34.4%) and was significantly associated with ciprofloxacin resistance (65.7% vs. 14.5%, p < 0.001). Among CTX-M-positive isolates (n = 31), group 1 predominated (87.1%), followed by group 2 (41.9%) and group 9 (6.5%); group 1 + 2 co-detection occurred in 38.7%, and 6.5% remained untypeable. PMQR markers included qnrS (11.1%), qnrB (4.4%), and aac(6')-Ib-cr (8.9%). Phylogroup B2 was dominant (76.7%). ERIC-PCR identified 59 profiles with high diversity (Simpson's index 0.9898); 60.0% of isolates belonged to clusters (largest cluster n = 4), indicating high fingerprint diversity inconsistent with a single dominant outbreak clone.Conclusion Presumptive ST131 isolates were enriched among ciprofloxacin-resistant E. coli in this single-center cohort. These findings reflect local molecular surveillance patterns rather than population-level prevalence. The high ERIC-PCR diversity suggests multiple lineages rather than a single outbreak clone, underscoring the need for sustained molecular surveillance and antimicrobial stewardship.