Prevalence of Extended Spectrum β-Lactamase-Producing <em>Escherichia coli</em>, <em>Klebsiella pneumoniae</em> and<em> Enterobacter cloacae</em> in Wastewater Effluent in Blantyre, Malawi

Background/Objectives: Wastewater treatment plants (WWTP) serve as a sink for both antimicrobial residues and bacteria carrying resistant genes which are later disseminated into the environment, facilitating the spread of antimicrobial resistance. This study investigated the presence of extended spectrum beta-lactamase (ESBL) producing Escherichia coli (Ec), Klebsiella pneumoniae (Kp) and Enterobacter cloacae (Enc) in effluent from WWTP in Blantyre, Malawi, to generate evidence and provide baseline information for interventions. Methods: Selective chromogenic agar was used to identify ESBL-producing bacteria. Results: A total of 288 samples were collected between April, 2023 and March, 2024 and 97.6% (281/288) yielded one or more presumptive ESBL isolates. Bacterial growth was confirmed as 48.9% Ec (255/522), 33.0% Kp (172/522) and 10.0% Enc (52/522). Antibiotic susceptibility testing showed higher resistance to ceftriaxone (Ec, 100.0%; Kp, 98.3%; Enc, 100.0%) and lower resistance to meropenem (Ec, 6.3%, Kp, 1.2%; Enc, 3.8%) among the antibiotics that were tested. Multiple antibiotic resistance phenotypes were observed in 73.1% of the isolates with the most prevalent phenotype as AUG-SXT-DXT-CIP-GM-ATH-CRO (55, 15.7%). Conclusions: The study demonstrated ongoing environmental contamination with antibiotic resistant bacteria from sewage effluent. Therefore, the functionality of WWTP should be improved to minimize the release of these organisms into the environment.