Sorgen, A. (2020). The influence of wastewater treatment on community dynamics among antibiotic-resistant bacteria during treatment, stream release, and biosolids land application. Unc Charlotte Electronic Theses And Dissertations.
Wastewater treatment plants (WWTP) are a key link between anthropogenic activity and the environment, facilitating the development and horizontal transfer of antibiotic resistance among populations of commensal environmental microorganisms and clinical pathogens. It is vital to understand the ecological factors associated with antibiotic-resistant microbes, encompassing their origins, evolution, selection, and dissemination, focusing on WWTPs as they are suspected to be major hotspots for the evolution and propagation of antibiotic resistance. Extensive research has been conducted on clinically relevant antibiotic- resistant pathogens; however, investigations into environmental reservoirs of antibiotic- resistant determinants and their influence on clinical situations have only been considered recently. By identifying sources of antibiotic-resistant bacteria (ARB), their environmental distribution, and how anthropogenic factors affect dissemination, we can institute approaches to contend with antibiotic resistance.We have employed culture-dependent and -independent approaches to address the following aims: (1) determine changes in resistance levels, (2) evaluate the community structure in multiple environments when exposed to treated wastewater products, and (3) identify antibiotic resistance fitness costs to those with such phenotypes.Within this investigation of four WWTPs located in Charlotte, North Carolina, we have demonstrated that the release of treated wastewater into the Charlotte watershed does not significantly increase ARB abundance within environmental compartments. The highest concentrations of ARB were found in raw sewage and the preliminary treatment stages. These concentrations were reduced considerably with biological aeration treatment, and the final treated effluent resembled that of natural stream communities, indicating that the Charlotte Water WWTPs are effective in the removal of ARB and their associated resistance genes. Similar findings were observed with the application of the treated biosolids as fertilizers upon agricultural crop fields where the application of ARB-rich biosolid sources resulted only in an immediate increase in resistant communities, leveling off over time to pre-application levels. We also found that the acquisition of multiple antibiotic resistance genes does not necessarily confer a fitness disadvantage in those exhibiting multi-drug resistance. More resistant strains of Enterococcus faecium, strains harboring a greater number of resistance genes, showed no fitness costs to heat, cold, osmotic, acid, or oxidative stressors relative to less resistant strains.We did, however, demonstrate that the culturable fractions of total environmental source populations are higher than previously speculated. On average, 12.8% of the total bacterial population was recovered using standard plating techniques, with some proportions greatly exceeding the widely accepted 1% culturability ideology. Though higher percentages of the microbial population were cultivable, the overall makeup of the cultured fractions varied considerably from that of the natural communities with culturing biases favoring Gammaproteobacteria. With the increasing threat of antibiotic resistance within healthcare settings, it is imperative to gain a better understanding of the phenotypic and ecological characteristics displayed by these resistant bacteria outside of these clinical settings.