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

Abstract Background 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. Methods A total of 48 wastewater samples were collected during both the dry and wet seasons (May–December 2019) and analyzed for E. coli and ESBL-producing E. coli concentrations using TBX agar with and without cefotaxime supplementation. Antimicrobial susceptibility testing (AST) and ESBL confirmation were performed using the Kirby-Bauer disc diffusion method and the double-disk synergy test, and polymerase chain reaction (Endpoint PCR) assays were performed to identify ESBL genes and determine phylogenetic groups. Results All samples (n = 48) carried ESBL-producing strains. The concentrations of ESBL-producing E. coli ranged from 1.36 × 10⁴ to 3.30 × 10⁵ CFU/100 mL, whereas the ratio of ESBL-producing E. coli among the total E. coli population varied between 0.20% and 16.33%. All the 107 isolated ESBL-producing E. coli strains were multidrug resistant (MDR), with 100% resistance to beta-lactams (ampicillin, ticarcillin, cefalotin, cefotaxime, ceftazidime, cefepime, aztreonam) and high resistance rates to non-beta-lactam antibiotics, including ciprofloxacin (77.57%). Notably, no resistance was observed to imipenem. Molecular analysis identified CTX-M-type genes in all isolates, with bla CTX-M-1 group (89.71%) and bla CTX-M-8 group (88.78%) being the most prevalent. The bla CTX-M-15 variant, a subgroup of bla CTX-M-1, was detected in 96.88% of bla CTX-M-1 positive isolates. Additionally, bla TEM (31.77%) and bla OXA-1 (34.57%) were detected, while bla SHV and bla CTX-M-25 were absent. Phylogenetic analysis of 107 isolates revealed a diverse distribution across four phylogroups: A (37.38%), D (22.43%), B1 (14.02%), and B2 (5.67%). The predominance of phylogroup A, often associated with commensal strains, suggests fecal contamination as a primary source. However, the significant presence of phylogroup D, which is linked to extraintestinal infections, raises concerns about the dissemination of potentially pathogenic strains. Conclusion This study highlights the high prevalence of ESBL-producing E. coli in wastewater in Dakar. The detection of MDR strains, particularly those carrying CTX-M-15 and belonging to pathogenic phylogroups, underscores the urgent need for comprehensive surveillance, improved wastewater treatment, and public health interventions to mitigate the spread of antibiotic resistance in Senegal.