Ecological constraints of antibiotic resistant gram-negative coliforms in an urban riverine ecosystem

Abstract

The distribution of antibiotic resistant bacteria in surface water is largely unknown but nowhere is this information more critical to understanding ecosystem function and protecting public health than in urban streams. The environmental factors that drive the distribution of antibiotic resistant gram-negative coliforms were evaluated along the main corridor and tributaries of the Green-Duwamish River watershed of the Puget Sound. I collected 65 samples of water, biofilms and sediments, and used culture-based methods to evaluate the distribution of total levels of resistance to ampicillin, chloramphenicol, and tetracycline from a mixed population of organisms. Antibiotic resistance was spatially-explicit and largely partitioned between lactose fermenting and non-lactose fermenting coliforms at each site and Analysis of Similarity indicated that resistance was more dissimilar between stream compartment and functional process zone than longitudinal distance along the river. Antibiotic resistance was negatively correlated with river power and channel sinuosity at the reach scale and Distance-based Redundancy Analysis determined 59.1% of the explainable variance was due to the environment and 4.6% due purely to geographic distance at the watershed scale. Resistance to more than one antibiotic was most common in water samples from middle watershed tributaries and the middle watershed main stem, with gradients of 1-2%. These results indicate that antibiotic resistance among gram-negative coliforms is controlled primarily by niche ecology at the microbial scale, stream morphometry at the reach scale, and environmental forcing at the landscape scale.