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Updated: Aug 9, 2026
Detection of Foodborne Bacterial Pathogens from Individual Filth Flies
Published on: February 13, 2015
Factors affecting the transmission of salmonella by flies: natural resistance to colonization and bacterial
B Greenberg1, J A Kowalski, M J Klowden
1Department of Biological Sciences, University of Illinois at Chicago Circle, Chicago, Illinois 60680.
Abstract:
Groups of immobilized gnotobiotic houseflies, Musca domestica L., were mono-contaminated with graded doses of Salmonella typhimurium, bicontaminated with S. typhimurium and Proteus mirabilis, and multicontaminated with S. typhimurium and a mouse fecal flora. Of 45 flies fed an average of 22 Salmonella cells alone, 26 showed bacterial multiplication, up to 1.4 x 10(7) in one case. There was a fairly consistent increase in percentage of Salmonella excreters with increasing input, so that all flies given 10(4) and 10(5) cells shed Salmonella some time during an observation period of 8 to 13 days. Multiplication, however, reached higher levels in flies given 10(2) or 10(3) organisms. A high input was not necessary to produce a high proportion of Salmonella excreters. Among 22 flies given an average of 90 Salmonella cells, multiplication occurred in 17 and 18 became excreters. Antagonism between P. mirabilis and S. typhimurium, which was previously described in the blowfly maggot tract, also occurred in the gut of the adult housefly. With an input of 10(3) cells each of Salmonella and Proteus, there was a reduction of Salmonella excreters to 27% on the first day and elimination by the second day. With a normal fecal flora which contained no demonstrable P. mirabilis, 37% of the flies were still excreting Salmonella on the fourth day, but not by day 6; among flies fed Salmonella alone at the same input, the organism was excreted by 87% on the first day and 62% on the second day, and outputs continued for at least 8 days. Salmonella was lodged mainly in the mid- and hindgut 3 days after the infective meal, minimizing transmission through vomit. Comparison studies with the common green bottle fly, Phaenicia sericata Mg., showed it to be more resistant than the housefly to establishment and multiplication of S. typhimurium.
Insights
Houseflies can become Salmonella carriers even with low doses, but co-infection with other bacteria reduces Salmonella shedding. Houseflies are more susceptible to Salmonella than green bottle flies.
Area of Science:
- Veterinary Entomology
- Microbiology
- Food Safety
Background:
- Houseflies (Musca domestica L.) are known vectors of pathogens.
- Understanding Salmonella typhimurium (S. typhimurium) transmission dynamics in flies is crucial for public health.
Purpose of the Study:
- To investigate the susceptibility of houseflies to S. typhimurium infection.
- To evaluate the impact of co-infection with Proteus mirabilis (P. mirabilis) and a mouse fecal flora on S. typhimurium shedding in houseflies.
- To compare the susceptibility of houseflies to S. typhimurium with that of the common green bottle fly (Phaenicia sericata Mg.).
Main Methods:
- Gnotobiotic houseflies were experimentally infected with varying doses of S. typhimurium.
- Flies were also co-infected with S. typhimurium and P. mirabilis, or S. typhimurium and a mouse fecal flora.
- Bacterial shedding and multiplication were monitored over 8-13 days.
- Gut localization of Salmonella was assessed.
- Comparative infection studies were conducted with Phaenicia sericata.
Main Results:
- Houseflies showed S. typhimurium multiplication and shedding even with low initial doses (average 22 cells).
- Higher Salmonella excretion rates were observed with increasing input doses.
- Co-infection with P. mirabilis significantly reduced Salmonella shedding, with elimination by day 2.
- A normal fecal flora also reduced Salmonella shedding compared to mono-contamination.
- Salmonella primarily colonized the mid- and hindgut.
- Houseflies were more susceptible to S. typhimurium establishment and multiplication than Phaenicia sericata.
Conclusions:
- Houseflies are efficient carriers of S. typhimurium, with low doses sufficient for establishment and shedding.
- Gut microbiota and specific bacterial antagonists like P. mirabilis play a significant role in modulating Salmonella colonization and transmission.
- Houseflies represent a more significant vector for S. typhimurium compared to Phaenicia sericata.
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