Date of Award

Spring 2009

Document Type



Life & Environmental Sciences

First Advisor

Sam Alvey

Second Advisor

Jennifer Glowienka

Third Advisor

Grant Hokit


The phenomenon of antibiotic resistance has lead to heightened discussion on how these adaptations may have arisen with such universality. Why antibiotic resistance occurs in an unpredictable manner within bacterial populations is poorly understood. It has been observed that resistance to many respective antibiotics is seen within the same organism as part of one phenotype. Each class of antibiotic has a distinct mode of action suggesting that adaptation to one antibiotic would not necessary illicit resistance to another. This study evaluates and outlines the environmental contributions to these multiple antibiotic resistance phenotypes present in bovine of the Rocky Mountain region of western Montana. Fecal samples were obtained from eight sites; several sites were sampled on two occasions. E. coli isolated from bovine feces were evaluated using an antibiotic susceptibility test to disclose whether they displayed multiple drug resistance and what MDR phenotypes were associated with the environments from which they were collected.

The majority of E. coli isolates exhibited resistance to four to five drugs tested. Several sites with no longitudinal likeness displayed resistance more frequently and to greater numbers of antibiotics. In a temporal comparison sites selected for multiple collections expressed resistance phenotypes that varied over time. Of the respective antibiotics used in this study erythromycin, gentamisin, streptomycin, and tetracycline appeared habitually throughout the library. The most common multiple drug resistance phenotype was erythromycin-gentamisin-streptomycin occurring in the total collection with a frequency of 39-66%. Because the mode of action of each of these antibiotics is different, the occurrence of resistance to all three within one organism suggests the presence of a resistance plasmid.