Introduction: Wastewater-based epidemiology (WBE) is a valuable tool for monitoring public health risks, offering insights into the prevalence and antimicrobial resistance (AMR) of pathogens like Listeria monocytogenes in community settings. This study investigates the prevalence, AMR profiles and infection risks of L. monocytogenes in final effluents of three wastewater treatment plants (WWTPs) in the Eastern Cape Province, South Africa.

Methods: Presumptive L. monocytogenes in wastewater effluents were detected using standard plate count methods, followed by the confirmation and screening for nine virulence markers using polymerase chain reaction (PCR) assays. Antibiotic susceptibility of confirmed isolates against 18 antibiotics was done using the disk diffusion method, and relevant resistance genes were screened via PCR. The potential risk of infection attributed to L. monocytogenes was assessed using the Quantitative Microbial Risk Assessment (QMRA) modelling. Monte Carlo simulation with 10,000 iterations was used to characterise the risk.

Results: The prevalence of L. monocytogenes in wastewater effluents was statistically significant (P < 0.05), ranging from log10 1.00 CFU/100 ml to log10 3.75 CFU/100 ml. Of 280 presumptive isolates, 20 (7.1%) were confirmed, with virulence genes detected at varying frequencies: inlA (95%), inlB (90%), actA (85%), hlyA (80%), and iap (75%). High phenotypic resistance was observed to tetracycline (80%), doxycycline (65%), cefotaxime (50%), penicillin (30%), and chloramphenicol (60%), with resistance genes detected as follows: tetA (60%), tetB (55%), tetC (50%), sulI (40%), sulII (35%), aadA (30%), aac(3)-IIa (25%), blaTEM (20%), blaCTX-M group 9 (15%), blaVEB (10%), and AmpC (10%). The average annual infection risk of 6.70 × 10⁻² (range: 9.10 × 10⁻³ to 1.00) exceeded the World Health Organization standards.

Conclusion:This study highlights the utility of WBE in detecting the prevalence, AMR, and infection risks of L. monocytogenes, emphasizing its value as a critical tool for public health surveillance and risk mitigation.