Term of Award

Summer 2011

Degree Name

Master of Science in Biology (M.S.)

Document Type and Release Option

Thesis (open access)

Department

Department of Biology

Committee Chair

Dana Nayduch

Committee Member 1

Laura Regassa

Committee Member 2

Jonathan Copeland

Abstract

House flies (Musca domestica L), feed and breed in decomposing organic waste and therefore are constantly in contact with different species of microorganisms. Because house flies live in close proximity to human and animal habitats, they pose a danger of transmitting pathogenic microorganisms from diseased sources to new environments. To elucidate pathogen vector potential of house flies, this study investigated dose-dependent survivability of GFPexpressing Streptococcus pyogenes and Salmonella typhimurium SR11 within the fly alimentary canal both spatially via epifluorescence microscopy and quantitatively via culture-recovery. Adult house flies were fed known amounts of bacteria (high or low dose), and were dissected to remove the entire alimentary canal for microscopy or were homogenized and cultured at intervals within 24 h post-ingestion. Excreta also were cultured to determine transmission potential. Also investigated was the dose-dependent local intestinal epithelial immune response of house flies to S. pyogenes and S. typhimurium, where the upregulation of three antimicrobial peptides Defensin, Cecropin and Diptericin were investigated. Both bacterial dose and species affected survivability of these pathogens in the house fly alimentary canal. High dose of both species survived throughout the 24 h period. The number of viable S. typhimurium increased in 2 numbers in both high and low dose, whereas S. pyogenes decreased in number with time progression. Viable S. typhimurium were recovered in large quantities from excreta as compared to S. pyogenes. Both bacterial species and dose also affected the temporal, spatial and class of AMP expression profiles in the gut. In S. pyogenes-fed flies, only Defensin was regionally produced in midgut tissue. In contrast, tissues from flies that were fed S. typhimurium expressed both Cecropin and Diptericin. In both species, the higher dose of bacterial challenge induced greater AMP expression than the low dose. The region of the gut showing AMP expression in both bacterial challenges was mainly the midgut, and peak expressions correlated with high numbers of bacteria as determined by culture-recovery. Dose-dependent effects or survival and transmission of bacteria from house flies has significant implications on vector potential.

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