Abstract
Wastewater contamination and urbanization contribute to the spread of antibiotic resistance in aquatic environments. This is a particular concern in areas receiving chronic pollution of untreated waste via combined sewer overflow (CSO) events. The goal of this study was to expand knowledge of CSO impacts, with a specific focus on multidrug resistance. We sampled a CSO-impacted segment of the James River (Virginia, USA) during both clear weather and an active overflow event and compared it to an unimpacted upstream site. Bacteria resistant to ampicillin, streptomycin, and tetracycline were isolated from all samples. Ampicillin resistance was particularly abundant, especially during the CSO event, so these isolates were studied further using disk susceptibility tests to assess multidrug resistance. During a CSO overflow event, 82% of these isolates were resistant to five or more antibiotics, and 44% were resistant to seven or more. The latter statistic contrasts starkly with the upstream reference site, where only 4% of isolates displayed resistance to more than seven antibiotics. DNA sequencing (16S rRNA gene) revealed that ~35% of our isolates were opportunistic pathogens, comprised primarily of the genera Stenotrophomonas, Pseudomonas, and Chryseobacterium. Together, these results demonstrate that CSOs can be a significant source of viable clinically-relevant bacteria to the natural environment and that multidrug resistance is an important understudied component of the environmental spread of antibiotic resistance.
Highlights
Widespread, indiscriminate use of antibiotics in recent decades has stimulated a proliferation of antibiotic-resistant (AR) strains of bacteria, which are a major public health threat to millions of people worldwide
When sampled during clear weather, water quality of the two sites was quite similar except for a small increase in turbidity, bacterial abundance, and E. coli at the combined sewer overflow (CSO) site compared to upstream (Table 1)
We focused on CSO discharge as a potential reservoir of pathogenic bacteria and multidrug resistance (MDR) to an urbanized river
Summary
Widespread, indiscriminate use of antibiotics in recent decades has stimulated a proliferation of antibiotic-resistant (AR) strains of bacteria, which are a major public health threat to millions of people worldwide. Wastewater treatment plants are well-known hotspots for AR [1] due to high densities of bacteria in close proximity as well as the presence of contaminants, such as pharmaceuticals and heavy metals, that select for resistant organisms. Because these wastewater treatment facilities do not completely remove antibiotics, antibiotic-resistant bacteria, or antibiotic resistance genes [2], effluent causes chronic pollution of receiving water bodies (e.g., see [3,4,5,6,7])
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