Isolation of Salmonella enterica serovar Enteritidis from House Flies (Musca domestica) Found in Rooms Containing Salmonella serovar Enteritidis-challenged hens.

Authors: Holt, Peter; Geden, Christopher - Chris; Moore, Randle; Gast, Richard

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/31/2007
Publication Date: 10/1/2007
Citation: Holt, P.S., Geden, C.J., Moore, R.W., Gast, R.K. 2007. Isolation of Salmonella enterica serovar Enteritidis from house flies (Musca domestica) found in rooms containing Salmonella serovar Enteritidis-challenged hens. Applied and Environmental Microbiology.73:6030-6035.

Interpretive Summary: Many insect species have long been considered to be carriers of disease organisms and responsible for disease spread. The current study examined whether houseflies released into a room containing hens infected with Salmonella enterica serovar Enteritidis (S. enteritidis) would become colonized with the organism and, if so, how long did the colonization take, where in and on the fly did it occur, and are these flies capable of transmitting the S. enteritidis to other hens. A large percentage of flies became colonized with S. enteritidis within 24-48 hours of release into the room. The organism was equally found on the exterior and the interior of the flies, and those S. enteritidis found inside the fly were primarily found in the gut and rarely in the crop while no S. enteritidis was found in fly salivary glands. Contaminated flies released into a room containing uninfected hens were not able to transmit the organism to the hens while a percentage of hens receiving contaminated flies orally did become intestinally colonized, indicating that the S. enteritidis was still viable and capable causing infection. These results indicate that house flies residing in an S. enteritidis-contaminated poultry environment rapidly become contaminated themselves, both internally and externally, and could potentially serve as a mechanism of S. enteritidis spread to other individuals within a flock.

Technical Abstract: House flies (Musca domestica) released into rooms containing hens challenged with Salmonella enterica serovar Enteritidis (S. enteritidis) rapidly became contaminated with S. enteritidis. Forty to 50% of the flies were contaminated at 48 hours which increased to 50-70% at 4 and 7 days post exposure and then decreased to 30% at day 15. Initial attempts at recovering surface organisms for culture using a PBS rinse was largely unsuccessful while culture of internal contents readily recovered S. enteritidis. However, when 0.5% detergent was incorporated into the rinse, high bacterial recoveries were observed from both external and internal culture regimes, indicating equal distribution of the organism on and in the fly and a tighter interaction of the organism with the host than previously thought. S. enteritidis was isolated routinely from the fly gut, on rare occasion from the crop, and never from the salivary gland. Feeding contaminated flies to hens resulted in gut colonization of a third of the birds but release of contaminated flies in a room containing previously unchallenged hens failed to result in colonization of any of the subject birds. These results indicate that flies exposed to an environment containing S. enteritidis can become colonized with the organism and might serve as a source of S. enteritidis transmission within a flock situation.