Frequency and characteristics of extended-spectrum beta-lactamase-producing Escherichia coli in wastewater in Dakar, Senegal.

OBJECTIVE: This study aimed to investigate the occurrence, antimicrobial resistance profiles, and genetic characteristics of extended-spectrum beta-lactamase (ESBL)-producing E. coli in wastewater collected in Dakar, Senegal. RESULTS DESCRIPTION: All samples (n = 48) carried ESBL-producing isolates. The concentrations of ESBL-producing E. coli ranged from 1.4 × 10⁴ to 3.3 × 10⁵ CFU/100 mL, whereas the ratio of ESBL-producing E. coli among the total E. coli population varied between 0.2% and 16.3%. All the 107 isolated ESBL-producing E. coli isolates were multidrug resistant (MDR), with 100% resistance to beta-lactams (ampicillin, cefalotin, cefotaxime, ceftazidime, cefepime, aztreonam) and high resistance rates to non-beta-lactam antibiotics, including ciprofloxacin (77.6%). No resistance was observed to imipenem. CTX-M-type genes were present in all isolates, with blaCTX-M-1 group (89.7%) and blaCTX-M-8 group (88.8%) being the most prevalent. The blaCTX-M-15 variant, a subgroup of blaCTX-M- group1, was detected in 96.9% of blaCTX-M-1 positive isolates. Additionally, blaTEM (31.8%) and blaOXA-1 (34.6%) were detected, while blaSHV and blaCTX-M-25 group were absent. Phylogenetic analysis of 107 isolates revealed a diverse distribution across four phylogroups: A (37.4%), D (22.4%), B1 (14.0%), and B2 (5.7%). The predominance of phylogroup A, mainly associated with intestinal commensal carriage, suggests fecal contamination as a primary source.