Date on Senior Honors Thesis


Document Type

Senior Honors Thesis

Degree Name




Author's Keywords

antibiotic; resistant; bacteria; water; Louisville


Antibiotic resistant bacterial strains are an increasing problem, particularly in clinical health care settings. As a result, bacterial infections are becoming increasingly challenging to treat with more cases becoming life threatening. Aquatic environments facilitate microbial diversity and the transfer of genetic elements and thus may serve as a reservoir for antibiotic resistant microbes. Human misuse of antibiotics may further facilitate the spread of resistance in water environments. With little known about the bacteria communities in local water environments, this study aimed to learn more about these populations through the following aims: 1) identify the microbial community composition from water environments around Louisville, KY; and 2) examine of the communities were resistant to two clinically used antibiotics—vancomycin and colistin. In this study, water sites were sampled and sorted into 4 categories: agricultural waters, commercial drains, natural waters, and wastewaters. In total, 155 single colony isolates resistant to vancomycin and colistin were identified through 16S sequencing. Whole community metagenomics analysis characterized the bacterial composition of 87 communities from the initial sample collection. Community diversity and the relationship between diversity and income was analyzed. One of the most striking results was the presence of Ochrobactrum sp. in 78 of the 87 communities. Two of the most prevalent genera, Ochrobactrum and Pseudochrobactrum, were characterized by assessing relative antibiotic resistance profiles and were found to be tolerant to high doses of a spectrum of antibiotics. Finally, a representative Ochrobactrum sp. isolate was tested for its ability to confer antibiotic resistance to a susceptible recipient bacterium. This Ochrobactrum sp. isolate was unable to transfer colistin resistance to another bacterial species, Pseudomonas aeruginosa, despite repeated efforts. The results indicate that there is a large diversity of microbes resistant to vancomycin and colistin though the ability of these microbes to transfer this resistance remains to be seen.

Lay Summary

The development of antibiotic resistant bacteria is a great concern to public health, especially with reports of bacterial resistance to important last resort antibiotics, such as vancomycin and colistin. Additionally, freshwater environments can be reservoirs of bacterial diversity and can facilitate the spread of antibiotic resistance genes. This study analyzes antibiotic resistant bacteria found in freshwater communities throughout Louisville, Kentucky and analyzes the antibiotic resistance profiles of two common genera: Ochrobactrum and Pseudochrobactrum.