Mehdi Bozorgi Mazandarani, Mohammad Kargar, Farshid Kafilzadeh,
Volume 20, Issue 1 (1-2026)
Abstract
Background: The emergence of fluoroquinolones (FQ) resistance in the Escherichia coli (E. coli) sequence type 131 (ST131) has become a major challenge in the management of urinary tract infections (UTI). Chromosomal mutations and plasmid-mediated quinolone resistance (PMQR) determinants play an important role in the FQ resistance.
Methods: This cross-sectional study was conducted in 2020 on 300 urine samples. aimed to investigate the prevalence of the chromosomal mutations, the PMQR genes including qnr, aac (6′)-Ib-cr, and efflux pumps among the FQ-resistant ST131 and non-ST131 E. coli causing UTI. Initially, the ST131 clone was detected using allele-specific PCR and confirmed by multilocus sequence typing.
Results: Among 95 FQ-resistant E. coli isolates, 30% (n=29/95) as belonging to the ST131 clone. The most frequently detected PMQR genes in FQ-resistant isolates were aac(6)’-lb-cr and qnrS. However, statistical analysis revealed a stronger association between aac(6ʹ)-Ib-cr and the ST131 clone (62%; p<0.03). The oqxA gene was the most prevalent efflux pump gene observed in both ST131 (n=11; 38%) and non-ST131 (n=16; 24%) isolates. Analysis of the gyrA and parC genes revealed significantly higher in ST131 compared to non-ST131. Double mutations, S80I+E84V, were significantly more prevalent in both gyrA (76% ST131 vs. 43% non-ST131; p=0.004) and parC (55% ST131 vs. 26% non-ST131; p=0.002). High-level resistance (MIC ≥32 μg/mL) observed in 96.6% (n=28/29) of ST131 isolates compared to 65% (n=43/66) of non-ST131 isolates.
Conclusion: The double mutations confer high level resistance to FQs in ST131 clone. These findings on resistance mechanisms can guide infection control strategies.
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