Dose-dependent effects on survival of Salmonella enterica serovar Typhimurium in house flies (Musca domestica L.)

Authors: CHIFANZWA, RABECCA - Georgia Southern University; Nayduch, Dana

Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/8/2017
Publication Date: N/A
Citation: N/A

Interpretive Summary: Adult house flies ingest variable numbers of bacteria when they encounter microbe-rich substrates. Bacterial abundance may affect survival within the fly gut, which subsequently impacts vector potential. This study investigated the dose-dependent survival of GFP (green fluorescent protein)-expressing Salmonella enterica serovar Typhimurium (GFP S. Typhimurium) within the fly digestive tract. Adult house flies were fed two doses (expressed as colony forming units, CFU) of GFP S. Typhimurium (high, ~350,000-410000 CFU and low, ~15,000 CFU). Bacteria were examined at 2, 4, 6, 12 and 24 h post-ingestion (PI) in the digestive tract using a flourescent microscope (to see the green fluorescing bacteria) and enumerated by culture using selective media. In both treatment groups, GFP S. Typhimurium proliferated and persisted in flies for 24 h. In the high dose group, the number of bacteria peaked at 6 h PI (a >500% increase from the amount that was fed). In the low dose group, the number of bacteria peaked at both 4 and 6 h PI (a >900% increase from the amount that was fed). Dose significantly affected bacterial survival within the house fly alimentary canal, particularly at 4, 6 and 12 h PI (P<0.05). The ability of S. Typhimurium to proliferate, survive and persist in the alimentary canal demonstrates that house flies may serve as significant reservoirs and probable disseminators of this pathogen. Our results show that bacterial abundance should be considered when assessing the potential of house flies to harbor and transmit pathogens.

Technical Abstract: Adult house flies ingest variable numbers of bacteria when they encounter microbe-rich substrates. Bacterial abundance may affect survival within the fly gut, which subsequently impacts vector potential. This study investigated the dose-dependent survival of GFP-expressing Salmonella enterica serovar Typhimurium (GFP S. Typhimurium) within the fly alimentary canal. Adult house flies were fed two doses (colony forming units, CFU) of GFP S. Typhimurium (high, ~10^5 CFU and low, ~10^4 CFU). Bacteria were examined at 2, 4, 6, 12 and 24 h post-ingestion (PI) in situ in the gut via epifluorescence microscopy and enumerated by culture on selective media. In both treatment groups, GFP S. Typhimurium proliferated and persisted in flies for 24 h. In the high dose group, proliferation peaked at 6 h PI (>500% increase). In the low dose group, proliferation peaked (>900% increase) at both 4 and 6 h PI. Dose significantly affected bacterial survival within the house fly alimentary canal, particularly at 4, 6 and 12 h PI (P<0.05). The ability of S. Typhimurium to proliferate, survive and persist in the alimentary canal demonstrates that house flies may serve as significant reservoirs and probable disseminators of this pathogen. Our results show that bacterial abundance should be considered when assessing the potential of house flies to harbor and transmit pathogens.