Introduction: Hospital wastewater is a major environmental reservoir for antibiotic-resistant bacteria (ARB) and resistance genes. In rapidly urbanizing regions like Dhaka, inadequate wastewater treatment enables the uncontrolled release of multidrug-resistant (MDR) pathogens into natural water bodies. Enterobacteriaceae, including Escherichia coli, Klebsiella pneumoniae, and Salmonella spp., serve as key indicators of antimicrobial resistance (AMR) in healthcare effluents. Discharge of such effluents facilitates the environmental spread of Extended-Spectrum Beta-Lactamase (ESBL)-producing strains. This study aimed to isolate, identify, and characterize Enterobacteriaceae from hospital wastewater, focusing on their phenotypic resistance patterns and molecular mechanisms underlying β-lactam antibiotic resistance.
Methodology: Wastewater samples were collected from major hospitals in Dhaka. Forty Enterobacteriaceae isolates were recovered using selective media and identified via biochemical tests (IMViC, urease, H₂S, motility, lactose fermentation) and the API 20E system (>88% accuracy). Antibiotic susceptibility against 15 clinically relevant drugs, including β-lactams, carbapenems, and aminoglycosides, was assessed using the Kirby–Bauer disc diffusion method. Representative ESBL-producing isolates underwent PCR to detect bla-TEM, bla-SHV, and bla-CTX-M genes, allowing correlation of genotypic and phenotypic resistance.
Results:Predominant isolates included E. coli, K. pneumoniae, Salmonella Typhi, Shigella spp., Proteus spp., and Enterobacter spp. High resistance was observed against Amoxicillin (44.44%), Ceftazidime (41.67%), and Ceftriaxone (38.89%), with lower resistance for Meropenem (19.44%) and Gentamicin (16.67%). ESBL production was detected in 53.5% of isolates, 44.34% were MDR, and 11.20% XDR. PCR revealed bla-TEM in 75% of ESBL-positive isolates, while bla-SHV and bla-CTX-M were each found in 25%, indicating active horizontal gene transfer.
Conclusion: Dhaka hospital wastewater serves as a significant reservoir of MDR and ESBL-producing Enterobacteriaceae. The predominance of bla-TEM emphasizes its role in environmental dissemination of β-lactam resistance. These findings highlight the urgent need for systematic AMR surveillance, antibiotic stewardship, and advanced wastewater treatment to mitigate environmental and public health risks.