DETECTION OF AIRBORNE SALMONELLA ENTERITIDIS IN THE ENVIRONMENT OF EXPERIMENTALLY INFECTED LAYING HENS BY AN ELECTROSTATIC SAMPLING DEVICE

Authors: Gast, Richard; Mitchell, Bailey; Holt, Peter

Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/30/2003
Publication Date: 4/5/2004
Citation: Gast, R.K., Mitchell, B.W., Holt, P.S. 2004. Detection of airborne salmonella enteritidis in the environment of experimentally infected laying hens by an electrostatic sampling device. Avian Diseases. 48:148-154.

Interpretive Summary: Contamination of the edible contents of table eggs with Salmonella enteritidis is an internationally significant cause of human illness. Because infected hens can deposit S. enteritidis inside eggs before they are laid, identifying infected flocks is an important objective in efforts to reduce the transmission of this pathogen to consumers. Testing to detect the presence of S. enteritidis in the poultry house environment has been the most common approach for determining whether laying flocks are infected. Because dust and aerosols that circulate in the air can carry bacteria, testing air samples could offer an efficient and inexpensive alternative for detecting S. enteritidis in poultry house environments. In this study, an experimental electrostatic sampling device was evaluated for its ability to detect S. enteritidis in the air of a room that housed infected laying hens in individual cages. Air samples were collected onto agar plates with the electrostatic device, a commercially available impaction sampler, and by passive exposure to the settling of aerosols and dust. Air samples were positive for S. enteritidis throughout the 4 weeks following inoculation of the hens. The electrostatic device led to more frequent and more numerous recovery of S. enteritidis colonies on agar plates than was obtained by passive exposure and performed similarly to the much more expensive impaction sampler. When used to expose agar plates to air for a period of 3 hours, the electrostatic device was able to detect S. enteritidis at a 75% frequency over the 4 weeks of the study.

Technical Abstract: Bacteriological culturing of environmental samples taken from sources such as manure pits and egg belts has been the principal screening tool in programs for identifying commercial laying flocks that produce eggs contaminated with Salmonella enteritidis. Because airborne dust and aerosols can carry bacteria, air sampling offers a potentially efficient and inexpensive alternative for detecting S. enteritidis in poultry house environments. In the present study, an electrostatic air sampling device was applied to detect S. enteritidis in a room containing experimentally infected, caged laying hens. After oral inoculation of hens with a phage type 13a S. enteritidis strain, air samples were collected onto agar plates with the electrostatic sampling device, an impaction air sampler, and by passive exposure to the settling of aerosols and dust. Even though the floor of the room was cleaned once per week (removing most manure, dust, and feathers), air samples were positive for S. enteritidis for up to 4 weeks post-inoculation. Based on both the number of S. enteritidis colonies observed on incubated agar plates and the frequency of positive results, the efficiency of the electrostatic device was significantly greater than that of the passive exposure plates (especially at short collection intervals) and was similar to that of the far more expensive impaction sampler. The electrostatic device, used for a 3-hour sampling interval, detected airborne S. enteritidis on 75% of agar plates over the 4 weeks of the study.