Antibiotic Resistance Among E.coli Isolates Within Hospital Wastewater Compared to Urban Wastewater

Jennifer Sheridan, “Antibiotic Resistance Among E.coli Isolates Within Hospital Wastewater Compared to Urban Wastewater”
Mentor: Troy Skwor, Biomedical Sciences

In the United States, each year 2.8 million people acquire antibiotic resistant infections. Of these, the CDC has identified carbapenem-resistance and extended spectrum beta-lactamase-producing Enterobacteriaceae as urgent and serious public health threats respectively. Our study focus was to investigate the prevalence of antibiotic resistance among Escherichia coli isolates and their corresponding antibiotic resistance genes (ARGs) from hospital wastewater and throughout the urban wastewater system, including assessing the potential impact of chlorination on resistant populations. Antimicrobial susceptibility of 124 E. coli isolates was determined using Kirby-Bauer disk diffusion assay for 12 antibiotics, as well as minimum inhibitory concentrations (MIC) assays on some resistant populations, and PCR used to determine the presence of ARGs and type 1 integrons among resistant isolates. The average multiple antibiotic resistance (MAR) index was significantly greater in hospital isolates compared to urban influents (0.220 vs 0.029 respectively). Of these, multi-drug resistance (3 or more antibiotic groups) was highest among hospital isolates (29.73%) followed by pre-chlorinated effluents (3.57%) and urban influents (0%) equal to post-chlorination (0%). All isolates were susceptible to carbapenems, but the hospital isolates had the highest prevalence of third-generation cephalosporin resistance which associated with extended-spectrum β-lactamase (ESBL) producers where blaCTX-M-15 was detected in 90% of the isolates. Of the tet genes analyzed, tetA and tetB were the most abundant, with the presence of both genes correlating with the higher MIC. Class 1 integrons were most abundant among hospital isolates, where over half carried a class 1 integron encoding a couple of ARGs. Our results highlight the overwhelming presence of MDR E. coli isolates within hospital wastewater, although their continual presence throughout the wastewater system appears minimal.

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