Streambed immobilization controls the transport of antibiotic resistance genes in flowing water.

Antibiotic resistance is a serious global health issue, resulting in at least 1.2 million deaths in 2019. The environment is a potentially important reservoir of antibiotic resistance; however, the fate of Antibiotic Resistance Genes (ARGs) in the environment remains poorly characterized. One important environmental source of ARGs is manure used as a soil amendment. ARGs from manure may then enter nearby flowing waterbodies, where the factors governing their downstream transport remain unknown. To address this, we conducted experiments by spiking cattle manure in an artificial stream to estimate removal rates (k; m-1) for three ARGs (mefA, tetQ, and tetW) and a ruminant fecal marker (bacR). We then used a Stochastic Mobile-Immobile Model (SMIM) to separate the overall removal into two components, rs, and rh, corresponding to immobilizations in the surface (i.e., water column) and subsurface (i.e., streambed), respectively. Finally, we applied the SMIM across four model streams to predict the downstream travel distance of ARGs and bacR. Our results showed measurable removal for all targets in all experimental replicates (n = 3) and no differences were found in the removal rates among replicates for any target (ANCOVA; p > 0.05). We found that the removal of bacR was significantly lower than tetW (p < 0.05) and slightly lower than mefA (p = 0.088), while tetQ removal was slightly different from tetW's (p = 0.072). We also found that rh values were orders of magnitude larger than rs for ARGs and bacR (t-test; p < 0.05). These findings suggest that ARGs and bacR are being removed from the water column through immobilization reactions occurring in the streambed. Additionally, we predicted that the 90 % removal (or D90) of targets occurs within the first 500 m in all model streams except in a slow-flow pastoral stream, which required 1400 m of downstream transport for 90 % removal. Our findings and model stand out as promising tools to predict the fate of ARGs in streams and will contribute to improving and managing agricultural practices that employ animal manure.

Assessment of antibiotic resistant coliforms from bioaerosol samples collected above a sewage-polluted river in La Paz, Bolivia.

Antimicrobial resistance is a global health risk, and the presence of resistant bacteria in the environment may be an indicative of fecal pollution. The objective of this study has been to assess the antibiotic resistance of airborne coliforms near a highly impacted urban river that may contain high levels of fecal waste. The pilot study has been located within an Andean river basin, the Choqueyapu River basin, which flows through La Paz city in Bolivia. Bioaerosol samples have been collected using liquid impingement and plated on mTEC agar. Coliforms have been detected within 80% of the air samples. The resistance profiles of coliforms present in 20 air samples have been determined by using a modified Kirby-Bauer disk diffusion test against amoxicillin-clavulanic acid, ciprofloxacin, gentamicin, meropenem, sulfamethoxazole-trimethoprim, and tetracycline, antibiotics commonly used to treat gram-negative infection. Broad patterns of antibiotic resistance have been observed throughout the study, with coliforms from at least one sample exhibiting resistance to each of the tested antibiotics. Resistance to sulfamethoxazole and amoxicillin-clavulanic acid has been the most commonly observed, with coliforms in 73% and 60% of samples which helps to demonstrate resistance to these antibiotics, respectively. This study provides insight into the prevalence of airborne, antibiotic resistant coliforms near concentrated fecal waste streams and this highlights an underappreciated hazard and the potential exposure risk in areas where fecal waste may become aerosolized at any given time.