Wastewater Systems Identified as "Ecological Superspreaders" of Antibiotic Resistance Genes in South African Urban Centers

Stellenbosch University study finds that "extracellular DNA" in South African wastewater acts as a superspreader for antibiotic resistance genes.

By: AXL Media

Published: Mar 31, 2026, 5:16 AM EDT

Source: Information for this report was sourced from Stellenbosch University

The Hidden Reservoir: Extracellular DNA

Antimicrobial resistance (AMR) is a global health crisis predicted to cause 10 million deaths annually by 2050. While much focus has been placed on living "superbugs," new research from Stellenbosch University highlights a previously underappreciated threat: extracellular DNA (exDNA). This is genetic material released into the water when bacteria are killed during the wastewater treatment process. Unlike the living bacteria, this "free-floating" DNA is not always destroyed by standard treatment methods. It remains in the effluent, capable of being absorbed by other living bacteria in the environment—essentially teaching them how to resist antibiotics.

A Toxic "Melting Pot" in Urban Infrastructure

Wastewater treatment plants (WWTPs) in large South African cities often act as a focal point for pollutants from diverse high-risk sources, including hospitals, abattoirs, and industrial sites. Dr. John Paul Makumbi, lead author of the study, describes these facilities as a "toxic melting pot." Here, bacteria are over-exposed to a concentrated mix of antibiotics and chemicals, accelerating their natural evolution toward resistance. Older WWTPs were designed to remove organic waste and kill live pathogens, but they were never engineered to filter out or neutralize the genetic material (exDNA) that carries resistance instructions.

Tracking High-Risk Bacterial Groups

The research team sampled nine WWTPs and connected river systems across Tshwane. Their microbiome analysis identified genetic material from two specific bacterial groups known for high-risk, multi-drug-resistant profiles: Pseudomonadota and Bacteroidota. Even after the water underwent standard treatment, the resistant genes from these groups persisted. This allows the WWTPs to function as "superspreaders," shaping the genetic landscape of freshwater ecosystems and potentially re-introducing resistance into human populations through water reuse or river contact.