Term of Award

Fall 2012

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

Lance Durden

Committee Member 2

James Claiborne

Committee Member 3

James Claiborne

Abstract

House flies (Musca domestica L.) feed and breed on septic substrates, putting them in direct contact with a multitude of disease causing agents and can act as a bridge for those agents to humans. The house fly has previously been shown to carry many different species of bacteria that are pathogenic. Escherichia coli O157:H7 is a pathogenic enterohemorrhagic serotype of E. coli that can be vectored by the house fly. Bacillus cereus is a foodborne pathogen that has also been isolated from the house fly in previous studies. To examine vector potential for these pathogens, house flies were fed green fluorescent protein (GFP)-expressing E. coli 157:H7 or B. cereus and then bacterial fate and localization of fly defensive responses were analyzed at various hours post-ingestion (h PI). Bacterial fate was assessed qualitatively by localizing bacteria via microscopy and quantitatively by culturing whole fly homogenate. House fly defensive responses, including three antimicrobial peptides (AMPs; Defensin, Diptericin, and Cecropin) and the peptidoglycan cleaving enzyme Lysozyme, were analyzed using immunofluorescent localization. Localization of B. cereus and E. coli O157:H7 at various time points correlated with evidence of lysed bacteria in microscopy, a decrease in recovered bacteria, and observed expression of AMPs and Lysozyme. Bacterial recovery showed that B. cereus decreased steadily up to 24 h PI and E. coli O157:H7 decreased steadily up to 12 h PI. Flies fed B. cereus induced Defensin, Diptericin, and Lysozyme expression that peaked in the midgut at 6 h PI. In contrast, flies fed E. coli O157:H7 showed noticeable expression of only Lysozyme and Diptericin at 2 and 6 h PI in the midgut and proventriculus. This study shows that B. cereus elicits a strong immune response from the house fly and can persist in the gut until 24 h PI, while E. coli O157:H7 elicits little immune response and can persist up to 12 h PI. These findings help to define whether or not pathogenic bacteria can survive at infectious levels within the fly, how the house fly responds to ingestion of these pathogens, and finally how long the bacteria can persist within the fly.

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