Term of Award

Summer 2011

Degree Name

Master of Science in Biology (M.S.)

Document Type and Release Option

Thesis (restricted to Georgia Southern)

Copyright Statement / License for Reuse

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.


Department of Biology

Committee Chair

Dana Nayduch

Committee Member 1

Oscar Pung

Committee Member 2

William Irby

Committee Member 3



House flies feed and reproduce in decomposing material such as feces and garbage. Since they are synanthropic and feed indiscriminately, house flies are potential vectors involved in the transmission of human bacterial diseases. The amount of bacteria flies ingest from their environment varies depending on the substrate. Likewise, flies are tolerant to particular levels of ingested bacteria. It has been demonstrated in Drosophila melanogaster that the dose-dependent tolerance to bacteria is immune-regulated. Besides the immune response, the fly gut has other physical and chemical defenses, which may serve in immobilizing and lysing ingested bacteria. This study investigated the dose dependent survivability of GFP-expressing Escherichia coli (GFP E. coli) in the fly alimentary canal and transmissibility of each bacterial dose was assessed by culturing excreta and also from food substrate. Four different doses of GFP E. coli (very low, low, medium and high, which corresponded to a 1046, 7266, 74000 and 726667 CFU, respectively) were fed to flies and survivability was determined quantitatively via culture-recovery at 1, 4, 10 and 22 h PI. Culture recovery, irrespective of dose, showed that GFP E. coli decreased in number temporally, from the amount initially fed. Statistical analysis showed that the decline in survivability of GFP E. coli was significant, except for very low dose-fed flies. Pair wise comparisons across bacterial dose within each time point revealed significant affects of dose on the survivability of GFP E. coli across all time points. For instance, survival, expressed as change in survival (Δ S), was significantly affected by dose ingested (P < 0.05), for all dose comparisons at all time points, but similar differences were observed in percent survival (% S) at 10 and 22 h PI only. Epiflourescence microscopy of GFP E. coli in the alimentary canal showed viable cells in the hindgut even at 22 h PI except for low dose-fed flies (1240 CFU). Flies that were fed with a high dose of GFP E. coli (over 105 CFU) disseminated an average 7990 CFU via vomitus within 4 h PI, and orally contaminated a food source with 436 CFU at 9 h PI. Understanding the dose-dependent survivability of GFP E.coli in house flies can help in quantitatively assessing the dissemination potential risks of flies that encounter different doses of bacteria.

Research Data and Supplementary Material