Master's Theses



Degree Name

Master of Science (MS)


Antibiotics are used in human medicine as well as agriculture. In the United States thousands of tons of antibiotics are annually given in low levels to livestock as prophylactics and to promote growth. This is in addition to antibiotic treatments needed when they have a bacterial infection. Antibiotics used in human medicine, such as penicillin, have shown a general trend of decreasing effectiveness that has been attributed in part to overuse or improper use. The use of antibiotics in agriculture might lead to similar resistance patterns. This might render antibiotics and their analogs less effective when needed in a clinical setting. To examine current resistance trends, soil samples were collected from pens at ten beef cattle feedlots across western Kansas. Soil samples were screened for bacteria resistant to ciprofloxacin, chloramphenicol, and tetracycline, all of which are considered broad spectrum antibiotics. Each antibiotic was tested at a concentration of 100[micro] g mL[-1]. Some bacteria isolates showed single drug resistance while others showed resistance to more than one antibiotic. Half of the antibiotics produced each year in the United States are used in human medicine. After antibiotics are administered they might pass through the patient and leave the body without being completely metabolized. This might contribute to an enormous amount of antibiotics entering sewage wastewater. The selection for antibiotic resistant bacteria might occur in sewage wastewater. Bacteria might develop high levels of resistance and perhaps resistance to multiple antibiotics. The mechanisms of horizontal gene transfer might facilitate the transfer of resistance genes within a bacterial population. Bacteria or their DNA might leave a sewage treatment plant (STP). Therefore, an understanding of antibiotic resistant bacteria leaving sewage treatment plants might be medically important to humans. I sampled the influent of five sewage treatment plants and isolated bacteria resistant to ciprofloxacin, chloramphenicol, and tetracycline, all broad spectrum antibiotics. I determined the minimum inhibitory concentration of each isolate and also determined multiple resistance to either ciprofloxacin, chloramphenicol or tetracycline. All sewage plants sampled contained bacteria resistant to at least one of the three antibiotics tested.


Eric Gillock

Date of Award

Spring 2007

Document Type

Thesis - campus only access


© 2007 Samuel Rich Zwenger


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