New research links water source type to antibiotic resistance

Aquatic environments are recognized as reservoirs and pathways for antimicrobial resistance, receiving antibiotic residues and resistant microorganisms from sewage, livestock farming, and aquaculture. Previous studies have detected resistance genes in drinking water sources and shown that conventional treatment may remove them incompletely. However, monitoring often focuses on individual pollutants or limited locations, leaving the relationships between antibiotic contamination, resistance genes, and bacterial resistance poorly understood. Rivers, enclosed reservoirs, and open lakes also differ in pollution exposure and water movement. In the Poyang Lake basin, which supplies drinking water sources for approximately 45 million people, a comprehensive comparison was needed to identify priority locations and factors associated with resistance.

A study (DOI: 10.48130/biocontam-0026-0010) published in Biocontaminant on 28 August 2026 by Huijun Ding's team, Nanchang University, identifies source type and mobile genetic elements as key factors associated with resistance-gene abundance.

The researchers sampled eight river sources and five sources classified as reservoir-type in December 2024 and June 2025, representing winter low-flow and summer high-flow conditions. Importantly, the latter group included Poyang Lake, an open, shallow lake hydrologically distinct from the four enclosed reservoirs. They screened water for 46 antibiotics using ultra-performance liquid chromatography coupled with tandem mass spectrometry, quantified eight resistance genes and an integrase gene using quantitative polymerase chain reaction, and tested antibiotic susceptibility in 178 cultured bacterial isolates.

Pollution-source analysis, risk assessments, and a partial least squares path model connected these measurements with season, water quality, and source type. Thirteen antibiotics were detected, with florfenicol and sulfamethoxazole reaching maximum concentrations of 72.85 and 30.51 nanograms per liter, respectively. Source analysis pointed to livestock farming, domestic sewage, and aquaculture as likely contributors. Ciprofloxacin, norfloxacin, and erythromycin posed moderate or high ecological risks at certain Gan River sites. Resistance genes were more abundant in summer, with sulfonamide resistance genes dominating at approximately 6,300 to 16 million copies per liter.

River sources generally showed higher gene-related risk scores, while the Poyang Lake site also stood out during summer. The path model identified mobile genetic elements as the strongest direct correlate of resistance-gene abundance, alongside a significant contribution from source type; seasonal influences operated mainly indirectly through mobile genetic elements. Among cultured isolates, resistance was most frequent to lincomycin, at 75.84%, and penicillin, at 53.95%. River isolates showed significantly higher resistance to these two antibiotics. However, average multiple-antibiotic resistance indices remained low in both seasons, and the overall index difference between river and reservoir groups was not statistically significant. Comparisons in selected isolates also revealed that carrying a resistance gene did not necessarily correspond to resistance in laboratory susceptibility tests, reinforcing the value of combining chemical, genetic, and bacterial measurements when assessing environmental resistance.

Together, the findings support differentiated monitoring that gives particular attention to river sources, the Gan River sub-basin, and Poyang Lake. They also show why resistance genes and bacterial susceptibility should be assessed alongside antibiotic residues. Broader genetic screening and repeated sampling could refine these priorities. Because the investigation examined source water, its results identify environmental concerns requiring management rather than demonstrating exposure or infection through treated drinking water.