Reuse irrigation cleared of antibiotic-resistance increase

Fears that antibiotic‑resistant bacteria are increased in the environment by the use of treated wastewater (TWW) for irrigation have been allayed by a study by researchers in Israel.

Human-impacted natural aquatic and terrestrial environments can serve as reservoirs of antibiotic‑resistance (AR) genes, which eventually decrease the effectiveness of antibiotic use in medicine.

The study, Impact of Treated Wastewater Irrigation on Antibiotic Resistance in Agricultural Soils published in Environmental Science & Technology, the American Chemical Society journal, set out to find the impact of the use of treated wastewater on soil AR bacteria and gene reservoirs. Tetracycline, erythromycin, sulfonamide and ciprofloxacin resistance in soil was assessed using standard culture-based isolation methods and culture-independent molecular analysis.

High levels of bacterial AR were detected in soils irrigated with both freshwater and reused wastewater. Nonetheless, in most of the soils analyzed, AR bacteria and gene levels in wastewater‑irrigated soils were on the whole identical (or sometimes even lower) than in the freshwater‑irrigated soils.

This indicates, say the researchers, that that the high number of resistant bacteria that enter the soils from the TWW are not able to compete or survive in the soil environment and that they do not significantly contribute AR genes to soil bacteria.

“This strongly suggests that the impact of the TWW‑associated bacteria on the soil microbiome is on the whole negligible,” says the paper, “and that the high levels of AR bacteria and AR genes in both the freshwater- and the TWW‑irrigated soils are indicative of native AR associated with the natural soil microbiome.”