Dose-dependent fate of GFP-E. coli in the alimentary canal of adult house flies

Authors: KUMAR H.V., NAVEEN - Georgia Southern University; Nayduch, Dana

Submitted to: Medical and Veterinary Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/9/2015
Publication Date: 6/1/2016
Citation: Kumar H.V., N., Nayduch, D. 2016. Dose-dependent fate of GFP-E. coli in the alimentary canal of adult house flies. Medical and Veterinary Entomology. 30(2):218-228. doi:10.1111/mve.12162.

Interpretive Summary: Adult house flies disseminate bacteria from microbe-rich substrates to areas where humans and domesticated animals reside. Because bacterial abundance fluctuates widely across substrates, flies encounter and ingest varying amounts of bacteria. We investigated the dose-dependent survival of bacteria in house flies. Flies were fed four different “doses” of GFP-expressing Escherichia coli (GFP E. coli; very low, low, medium, high, from 10e3 to 10e5 bacteria per fly) and survival was determined at 1, 4, 10 and 22 h post-ingestion via culture of whole homogenized flies and epiflourescent microscopy of the alimentary canal. Over 22 h, decline of GFP E. coli was significant for all treatments (P<0.04) except the very low dose (P=0.235). Change in survival (the amount recovered minus the amount fed) did not differ between flies fed low and very low doses of bacteria across all time points, although both treatments differed from flies fed high and medium bacterial doses at several time points. At 4, 10 and 22 h, GFP E. coli change in survival significantly differed between medium and high dose-fed flies. The low dose-fed flies excreted the highest percentage of the fed dose, but the high dose fed flies excreted the largest numbers of bacteria (although a low percentage of the fed amount). The medium dose fed flies excreted the lowest percentage of the fed dose. Flies fed either the medium or high doses of bacteria showed a large amount of bacteria destruction (lysis) when in the alimentary canal. A threshold dose, above which bacteria are detected and destroyed by house flies, may exist and likely is immune-mediated. Understanding dose-dependent bacterial survival in flies can help in predicting bacteria transmission potential.

Technical Abstract: Adult house flies (Diptera: Muscidae; Musca domestica L.) disseminate bacteria from microbe-rich substrates to areas where humans and domesticated animals reside. Because bacterial abundance fluctuates widely across substrates, flies encounter and ingest varying amounts of bacteria. We investigated the dose-dependent survival of bacteria in house flies. Flies were fed four different “doses” of GFP-expressing Escherichia coli (GFP E. coli; very low, low, medium, high, defined in text) and survival was determined at 1, 4, 10 and 22 h post-ingestion via culture and epiflourescent microscopy. Over 22 h, decline of GFP E. coli was significant for all treatments (P<0.04) except the very low dose (P=0.235). Change in survival (' S) did not differ between flies fed low and very low doses of bacteria across all time points, although both treatments differed from flies fed high and medium bacterial doses at several time points. At 4, 10 and 22 h, GFP E. coli ' S significantly differed between medium and high dose-fed flies. A threshold dose, above which bacteria are detected and destroyed by house flies, may exist and likely is immune-mediated. Understanding dose-dependent bacterial survival in flies can help in predicting bacteria transmission potential.