Isolation of Salmonella enterica serovar Enteritidis from houseflies (Musca domestica) found in rooms containing Salmonella serovar Enteritidis-challenged hens

Abstract

Houseflies (Musca domestica) released into rooms containing hens challenged with Salmonella enterica serovar Enteritidis (Salmonella serovar Enteritidis) rapidly became contaminated with Salmonella serovar Enteritidis. Forty to 50% of the flies were contaminated at 48 h, and the percentage increased to 50 to 70% at 4 and 7 days postexposure and then decreased to 30% at day 15. Initial attempts at recovering surface organisms for culture using an aqueous rinse were largely unsuccessful, while cultures of internal contents readily recovered Salmonella serovar Enteritidis. However, when 0.5% detergent was incorporated into the rinse, high recovery levels of bacteria were observed from both external and internal culture regimens, indicating equal distribution of the organism on and in the fly and a tighter interaction of the organism with the host than previously thought. Salmonella serovar Enteritidis was isolated routinely from the fly gut, on rare occasions 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 Salmonella serovar Enteritidis can become colonized with the organism and might serve as a source for transmission of Salmonella serovar Enteritidis within a flock situation.

FIG. 1.

Recovery of Salmonella serovar Enteritidis (SE) from flies captured in rooms containing infected hens. The results represent the percentage of flies (n = 20 flies/sampling day) that were positive for Salmonella serovar Enteritidis on each sampling day postchallenge in experiments 1, 2, and 3. Expt., experiment; *, flies sampled on day 9 postchallenge in experiment 3.

FIG. 2.

Concentrations of Salmonella serovar Enteritidis (SE) in feces that collected under cages of infected hens over different times postchallenge (n = 4 samples/time period). The results represent the log₁₀ Salmonella serovar Enteritidis cells/gram of feces at the sampling times noted for experiment 1 (Expt. 1) and experiment 2 (Expt. 2). ND, not determined.

FIG. 3.

Simple aqueous rinsing does not remove Salmonella serovar Enteritidis (SE) from fly exteriors. The results represent the percentage of flies that were positive for Salmonella serovar Enteritidis for each sample type in trial 1 (n = 14 flies/sample type) and trial 2 (n = 10 flies/sample type). The number within the bar is the statistical difference between the numbers of Salmonella serovar Enteritidis cells recovered from fly interiors and exteriors. ?, questionable lack of organism.