Master's Theses

Document Type

Thesis - campus only access

Date of Award

Spring 2009

Degree Name

Master of Science (MS)

Department

Biology

Advisor

Eric Gillock

Abstract

The most common type of antibiotics prescribed in the U.S. and worldwide for clinical infections are beta lactams. It is estimated that 28 million pounds of antibiotics a year are consumed in the U.S. with approximate equal usage between agriculture and medicine. Some percentage of an antibiotic dose given to a patient leaves the body unaltered, is disseminated, and can persist in the environment, putting selection pressure on populations of bacteria for antibiotic resistance. Bacteria that are able to survive exposure to an antibiotic will be able to reproduce, passing resistance to future generations. Also, bacteria that have resistance genes located on transferable plasmids can pass this resistance to other bacteria via horizontal gene transfer. This transfer of resistance genes might pose a significant threat to the medical community if non-resistant human pathogens acquire resistance from other bacteria and then limit the options of treating a patient's infection. Some bacteria have evolved a way to combat beta-Iactam antibiotics by producing beta-Iactamase enzymes that render the antibiotics useless. These extended spectrum beta-Iactamases (ESBLs) confer resistance to bacteria able to produce them. Most of the study of beta-Iactamase production has focused on clinical infections. Limited study has been done with beta-Iactamase producing bacteria isolated from human sewage. / To study the production of extended spectrum beta-lactamases (ESBLs) in bacteria from human sewage, I screened wastewater influent from the Hays, Ellis County, KS wastewater treatment plant on Mueller-Hinton Agar embedded with 50 microgram/milliliter cefotaxime. Cefotaxime was used due to its broad spectrum of activity against bacteria and also because it is a relatively “new" class of cephalosporin. I also screened the bacteria on MacConkey Agar, which is differential for lactose fermentation and selective for gram negative bacteria. Because gram positive bacteria are not thought to produce ESBLs, I limited this study to gram negative bacteria. I performed double disc diffusion assays and E-tests to look for the presence of extended spectrum beta lactamases (ESBLs). An isolate of Escherichia coli serotype 0157:117 was found to produce an ESBL, which conferred resistance to cefotaxime. In addition to resistance assays I viewed and photographed two of my isolates under a Scanning Electron Microscope (SEM). / The clinical implications of the overuse of all antibiotics had become apparent with the spread of multiple resistant Staphylococcus aureus (MRSA), and Escherichia coli O 157:H7. As newer classes of ESBLs evolve, the resistance problem only increases. Pathogenic species of bacteria have been able to pick up and transfer resistance genes, limiting therapeutic options for patients with infections. Adding to this problem is that non-pathogenic species of bacteria can act as "resistance gene reservoirs", harboring plasmids that can be exchanged with previously non-resistance species of bacteria. Without the prudent use of antibiotics, resistance will become an increasingly complex medical problem worldwide.

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© 2009 Jerad Gorney

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