Environmental surveillance of diarrheagenic Escherichia coli highlights spatial patterns of antimicrobial resistance and diarrheal risk along the Buffalo River, South Africa
1
University of Washington, Seattle, United States
Popul. Med. 2026;8(Supplement Supplement 1):
ABSTRACT
INTRODUCTION:
Surface waters serve as reservoirs for diarrheagenic and antimicrobial-resistant bacteria. This study applied environmental surveillance to examine spatial patterns of diarrheagenic Escherichia coli (DEC), antimicrobial resistance, and diarrheal risk along the Buffalo River, Eastern Cape province, South Africa.
METHODS:
Water samples were collected from four access points along the Buffalo River. E. coli were isolated, confirmed using polymerase chain reaction (PCR), and pathotyped for DEC. Antimicrobial susceptibility testing and PCR detection of resistance genes were performed. Diarrheal infection risk was estimated using microbial risk assessment with Monte Carlo simulation, and spatial variation in resistance was assessed using resistance indices and diversity metrics.
RESULTS:
Mean E. coli concentrations ranged from approximately 8.2 × 10² to 1.6 × 10³ CFU/100 mL across sites, exceeding guideline values at all access points. Of 200 presumptive isolates, 180 (90%) were confirmed as E. coli, and 50 (28%) were identified as DEC. Enterohemorrhagic E. coli accounted for up to 54% of DEC at some access points and was detected at all sites. Multidrug resistance was common, with 58% to 84% of DEC isolates resistant to three or more antibiotic classes. Mean multiple antimicrobial resistance indices ranged from 0.15 at upstream sites to 0.42 at downstream sites, with three access points exceeding the high-risk threshold of 0.2. Tetracycline- and β-lactam–associated resistance genes were detected in 30–62% of DEC isolates, and strong correlations were observed between phenotypic and genotypic resistance profiles (r = 0.83–0.93). Estimated annual diarrheal infection risks exceeded international guideline values at all access points.
CONCLUSIONS:
Environmental surveillance along the Buffalo River revealed consistently elevated diarrheal risk and substantial spatial variation in antimicrobial resistance among DEC. These findings support the use of surface water monitoring to guide water safety planning and antimicrobial resistance surveillance in communities reliant on untreated surface water.
Surface waters serve as reservoirs for diarrheagenic and antimicrobial-resistant bacteria. This study applied environmental surveillance to examine spatial patterns of diarrheagenic Escherichia coli (DEC), antimicrobial resistance, and diarrheal risk along the Buffalo River, Eastern Cape province, South Africa.
METHODS:
Water samples were collected from four access points along the Buffalo River. E. coli were isolated, confirmed using polymerase chain reaction (PCR), and pathotyped for DEC. Antimicrobial susceptibility testing and PCR detection of resistance genes were performed. Diarrheal infection risk was estimated using microbial risk assessment with Monte Carlo simulation, and spatial variation in resistance was assessed using resistance indices and diversity metrics.
RESULTS:
Mean E. coli concentrations ranged from approximately 8.2 × 10² to 1.6 × 10³ CFU/100 mL across sites, exceeding guideline values at all access points. Of 200 presumptive isolates, 180 (90%) were confirmed as E. coli, and 50 (28%) were identified as DEC. Enterohemorrhagic E. coli accounted for up to 54% of DEC at some access points and was detected at all sites. Multidrug resistance was common, with 58% to 84% of DEC isolates resistant to three or more antibiotic classes. Mean multiple antimicrobial resistance indices ranged from 0.15 at upstream sites to 0.42 at downstream sites, with three access points exceeding the high-risk threshold of 0.2. Tetracycline- and β-lactam–associated resistance genes were detected in 30–62% of DEC isolates, and strong correlations were observed between phenotypic and genotypic resistance profiles (r = 0.83–0.93). Estimated annual diarrheal infection risks exceeded international guideline values at all access points.
CONCLUSIONS:
Environmental surveillance along the Buffalo River revealed consistently elevated diarrheal risk and substantial spatial variation in antimicrobial resistance among DEC. These findings support the use of surface water monitoring to guide water safety planning and antimicrobial resistance surveillance in communities reliant on untreated surface water.
| eISSN: | 2654-1459 |
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