Date of Award


Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy in Biological Sciences (PhD)

Administrative Home Department

Department of Biological Sciences

Advisor 1

Stephen M. Techtmann

Committee Member 1

Ebenezer Tumban

Committee Member 2

Gordon Paterson

Committee Member 3

Daisuke Minakata


The increase in antimicrobial-resistant bacteria has posed challenges to treating resistant diseases. Antimicrobials such as nanoparticles (NPs) and biocides are commonly used to control microbial growth in household and industrial settings. Several studies have shown that bacteria that become resistant to biocides can also resist antibiotics. There are fewer reports of resistance to nanoparticles. Our study goals were to compare the environmental effects of biocides and nanoparticles by investigating their impacts on stream microbial community structure, the mechanism of bacterial resistance, and their interactions with natural organic matter (NOM). Our results showed that biocides dramatically altered microbial community composition and diversity in comparison to NPs. We used an experimental evolution approach to demonstrate that E. coli quickly acquired resistance to both biocides and NPs. We demonstrated that efflux pumps play an important role in resistance to DBNPA and Ag-NPs. Resistance to both Ag-NPs and DBNPA resulted from mutations in multiple genes such as flagellar genes and efflux pumps. We also demonstrated that NOM can interrupt the antimicrobial activity of Ag-NPs and DBNPA. Before this work, there were very few studies directly comparing the impacts of both NPs and biocides on microbial communities and how the microorganisms develop resistance to biocides and NPs on a molecular level. This work provides a comparison of the environmental effects of these antimicrobials as well as a comparison of the mechanisms of acquired resistance. Our findings support the importance of considering the environmental risk of Ag-NPs and DBNPA. This work shows that while nanoparticles resulted in fewer alterations to microbial community composition in microcosms from stream water, bacteria can rapidly develop resistance to nanoparticles. Novel technologies and comparative studies such as the one performed here are important for identifying strategies for microbial control that do not contribute to the spread of antimicrobial-resistant bacteria.