Department Chair

Daniel L. Potts, Ph.D.

Date of Award


Access Control

Open Access

Degree Name

Biology, M.A.


Biology Department


Gary W. Pettibone, Ph.D.

Department Home page

First Reader

Robert J. Warren II, Ph.D.

Second Reader

Derek L. Beahm, Ph.D.

Third Reader

Daniel L. Potts, Ph.D.


Antibiotic-resistant (AR) bacteria have been found in environmental ecosystems including beach sand and water, and pose a serious threat to the mitigation of human and animal disease. The presence of antibiotic residues in the environment, fueled by wastewater effluent and agricultural runoff, may produce selective pressure on introduced microbes such as Escherichia coli, leading to the production of AR populations. This study characterized and compared the antibiotic resistance patterns and plasmid content of E. coli isolated from a freshwater beach and clinical urinary tract infection (UTI) samples. A higher level of antibiotic resistance was expected in clinical (UTI) Escherichia coli isolates due to stronger selective pressure. A total of 171 beach isolates (comprised of 66 sampled from nearshore water and 105 sampled from sand) and 111 UTI isolates were screened by disk diffusion for microbial resistance to 11 antibiotics. More clinical UTI E. coli isolates were resistant to one or more of the antibiotics used in this study than were E. coli isolated from freshwater beach sand and adjacent near shore water (p < 2.2-16). Although previous studies have shown higher instances of antibiotic resistance in beach sand isolates than those from adjacent water, none of the E. coli isolated from sand showed resistance to any of the antibiotics tested. Eight percent of water isolates and 49% of UTI isolates demonstrated resistance to at least one antibiotic. Significant correlation was found between resistance to one or more of the antibiotics used in the study and plasmid content in UTI isolates, but there was no correlation between antibiotic resistance and plasmid content in isolates from sand or water. The data suggests that the Escherichia coli isolated from sand, lacking the selective pressure of antibiotic residues typical in clinical and wastewater environments, could represent members of naturalized populations.