Semester of Graduation
Master of Science (MS)
Since their initial discovery in 1928, antibiotics have been utilized for agriculture and human health purposes. The increasing use of antibiotics by humans and the rapid evolution of antibiotic resistance might be leading to the presence of more antibiotic-resistant bacteria in the environment. Understanding potential relationships between humans, bacteria, and the environment is important in order to study the spread and progression of antibiotic resistance in bacteria. Several past studies have focused on oxidative stress, temperature stress, and antibiotic resistance in bacteria, but to my knowledge few if any have done a wide comparison between these environmental stressors and the fitness of bacteria collected from songbirds. This study examined the responses of forty bacterial isolates cultured from seven songbird species to environmental stressors (oxidative stress and temperature) and evaluates whether the overall fitness of these bacteria in response to these conditions correlated with minimum inhibitory concentrations (MICs). This research uses growth rates calculated from four temperatures and survival percentages after exposure to four different concentrations of hydrogen peroxide (H2O2) over the course of 120 minutes to measure fitness. The MICs for the antibiotics erythromycin, ceftazidime, and ciprofloxacin were compared amongst isolates. In addition, bird species, sex, isolate origin, and age were included as variables. After these experiments were completed, analysis was completed to examine correlations. The isolates studied displayed differences in tolerance to hot and cold temperatures, but the growth rates at the temperatures examined displayed no correlation to MICs for the antibiotics tested. No relationships were observed between MICs and oxidative stress tolerance measured using H2O2 survival data. Analyses were performed to examine possible relationships between known isolate variables and the data collected from determining MICs, H2O2 survival percentages, and growth rate data. A difference in means was observed between isolate origin and H2O2 survival and between MICs and sample origin, although these differences were not statistically significant. These differences could be due to the variance in the bacterial microbiome and/or their intrinsic resistance. This study examined culturable antibiotic-resistant bacteria from songbirds and demonstrated their variable fitness, adaptability, and established preliminary data from which future studies will arise.
Forsyth, Leah R., "Antibiotic Resistance in Bacteria From Songbirds and Fitness Studies Following Environmental Stressors in vitro" (2020). LSU Master's Theses. 5069.