Molecular Detection of Extended-Spectrum-ββ-Lactamase-Producing and Fluoroquinolone-Resistant Escherichia coli isolated from Diarrheic Stools in Abuja, Nigeria

Background: The emergence of drug-resistant Escherichia coli in diarrheal cases showed the need for better monitoring of resistance pat-terns. This study analyzed fluoroquinolone resistance and ESBL genes in diarrheagenic E. coli isolates from Abuja, Nigeria. Methods: Fresh stool specimens obtained from study participants were subjected to microbiological culture, with subsequent identification of all Gram-negative isolates using the Analytical Profile Index (API) 20E system. Patient demographic data were systematically collected via structured questionnaires. Antimicrobial susceptibility testing of confirmed E. coli isolates was performed using a Kirby-Bauer disk diffusion assay. Molecular characterization included the detection of Extended-Spectrum ββ-Lactamase genes (blaSHV, blaCTX-M, and blaTEM) and quinolone resistance determinants (qnrB, qnrS, and oqxB) through multiplex PCR analysis using gene-specific primers. Results: Of the 380 stool samples processed, bacterial growth was observed in only 156 specimens (41%), while 224 samples (59%) showed no microbial growth. Among cultured isolates, Escherichia coli (n=40) demonstrated the highest prevalence, exhibiting notable resistance patterns: 75% to Augmentin (amoxicillin-clavulanate) and 63% to ceftazidime, with multidrug resistance (≥3 antibiotic classes) observed across all resistant strains. ESBL genotyping revealed the blaTEM gene in 21 E. coli isolates (52.5%). Quinolone resistance markers were detected at varying frequencies: qnr genes were present in 15% of isolates (6/40), with qnrS (5%) and qnrB (10%) specifically identified. Notably, the oqxB gene was absent in all tested specimens. Conclusions: This investigation revealed that E. coli isolates had a significant incidence of antimicrobial resistance, with ββ-lactam antibiotic resistance predominating. According to molecular characterisation, the most prevalent resistance determinant is the blaTEM ESBL gene. Furthermore, a subgroup of isolates had plasmid-mediated quinolone resistance genes (qnrB and qnrS) identified. Because of their plasmid-borne nature, which allows for horizontal gene transfer across bacterial strains and may hasten the spread of multidrug resistance within microbial populations, the existence of these mobile genetic elements is especially of significant concern.