Diversity of Multidrug-Resistant Bacteria in an Urbanized River: A Case Study of the Potential Risks from Combined Sewage Overflows

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.

Drivers of Antibiotic Resistance Gene Abundance in an Urban River

“…Fecal contamination is one of the main sources of ARGs in urban aquatic environments [ 25 ], in part due to increased population density and high levels of impervious surfaces [ 26 , 27 ]. Combined sewage overflow systems in urban settings are known to be a major source of ARGs and resistant bacteria to receiving waterbodies [ 12 , 14 , 28 ]. Our results suggest that while CSO events are likely a large source of ARGs in the river, non-point sources are also important sources of ARGs in the river.…”

“…We quantified the abundance of five ARGs: tetO and tetW for resistance to tetracyclines, bla TEM and ampC for β-lactam antibiotics, and qnrA for quinolones. These ARGs confer resistance to some the top prescribed antibiotics in the United States [ 69 ], and bacteria with resistance to the respective antibiotics have previously been detected at the two sites [ 12 ]. Each qPCR run included an appropriate standard curve that covered at least eight orders of magnitude, with the lowest starting point being 88 ( tetO ), 32 ( tetW ), 44 ( bla TEM ), 51 ( ampC ), and 156 ( qnrA ) gene copies per reaction.…”

Isolation, identification, and characterization of resistant bacteria to antibiotics from pharmaceutical effluent and study of their antibiotic resistance

“…Pharmaceutical discharges are the waste products of the pharmaceutical company generates during a drug’s manufacturing process ( Geta and Kibret, 2022 ). The pharmaceutical industry’s effluents contain antibiotics, prescription, and non-prescription drugs ( Balasa et al, 2021 ). Antibiotic resistance and hospital-acquired diseases can result from chronic antibiotic exposure.…”

Antibiotic Resistance Profiles of Bacteria Isolated from Hotspot Environments in Bahir Dar City, Northwestern Ethiopia

“…Antibiotic resistance is most commonly studied in the medical setting, but there is growing concern about the spread of antibiotics into the natural environment. 3 …”

“…Antibiotic resistance is most commonly studied in the medical setting, but there is growing concern about the spread of antibiotics into the natural environment. 3 Untreated wastes generated from humans (municipal wastes), health institutions (medical wastes), and animals are some hotspots that pose the risk of spreading antibiotic-resistant bacteria within the environment. Untreated effluents or the concentrated forms of infectious agents and antibiotic-resistant microbes are shed into communities, leading to waterborne diseases such as cholera typhoid fever, dysentery, and gastroenteritis, which cannot be treated with conventional antibiotics.…”