Genetic analysis of virulence, extended spectrum beta lactamase, and carbapenem resistance in Escherichia coli O157:H7 isolates from drinking water and wastewater in Addis Ababa, Ethiopia.

Escherichia coli O157 H7, a Shiga toxin-producing enterohemorrhagic strain, poses serious health risks and has increasingly acquired multidrug resistance (MDR) through extended-spectrum β-lactamases (ESBLs) and carbapenemases. This study investigated the molecular characteristics of E. coli O157:H7 isolated from drinking and surface wastewater in Addis Ababa, Ethiopia. A total of 205 water samples (97 drinking and 108 wastewater) were collected from Addis Ketema and Akaki/Kality sub-cities between May and July 2023. Isolation was performed using membrane filtration and confirmed by latex agglutination. Antimicrobial susceptibility testing followed CLSI (2023) guidelines, and conventional polymerase chain reaction (PCR) was used to detect virulence (stx1, stx2, eaeA, hlyA), ESBL (blaTEM, blaSHV, blaCTX-M), and carbapenem-resistance (blaNDM, blaKPC, blaOXA-48) genes. Among 28 confirmed isolates, 32.1% originated from drinking water and 67.9% from wastewater. Virulence genes were found in 35.7-57.1% of isolates, with eaeA and stx2 being the most frequent. ESBL genes were dominated by blaCTX-M and blaTEM (85% each). Carbapenemase genes were present in 28.6% of isolates, mainly blaNDM and blaKPC. Gene prevalence was significantly higher in Akaki/Kality (p < 0.05). These findings reveal wastewater as a major reservoir of pathogenic and resistant E. coli O157 H7 and highlight the urgent need for improved wastewater treatment and regular molecular surveillance.