Submitted to: Journal of Food Protection
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/4/2004
Publication Date: 8/1/2004
Citation: Gast, R.K., Holt, P.S. 2004. Incubation of Egg Contents Pools at an Elevated temperature (42 degrees Centigrade) Does Not Improve the Rapid Detection of Salmonella Enteritidis Phage Type 14b. Journal of Food Protection. 67(8):751-1754. Interpretive Summary: Detecting Salmonella Enteritidis inside eggs is important for protecting consumers against disease transmitted by contaminated eggs. Some new methods can detect S. Enteritidis contamination very rapidly, but these approaches typically require very large numbers of bacteria (as many as 10 million per ml) to be present. Because egg contamination typically involves very small initial numbers of S. Enteritidis cells, standard procedures for finding this pathogen in pools of liquid egg contents often include a preliminary incubation step to encourage bacterial multiplication to levels that can be consistently detected. The present study determined whether small initial numbers of S. Enteritidis (approximately 10 cells) would multiply fast enough in 10-egg pools incubated at 42° C to allow detection of contamination by a rapid lateral flow immunodiffusion test within a single 8-hour working day. Incubation at 42° C did result in significantly greater multiplication of S. Enteritidis after 6, 8, 10, and 12 hours than was observed at 37° C. However, 12 hours of incubation at 42° were required before S. Enteritidis contaminants were detected consistently in egg pools by the rapid test. Accordingly, detection of S. Enteritidis contamination within a single standard working day does not appear to be possible using current technologies for incubating and testing egg pools.
Technical Abstract: Detecting internal contamination of eggs with Salmonella enterica serovar Enteritidis (Salmonella Enteritidis) is essential for protecting public health. Pooling together 10 or more eggs for sampling allows many eggs to be screened for contamination, but such pools must be incubated at 25-37° C to permit small numbers of Salmonella Enteritidis to multiply before further testing. The present study determined whether incubating egg contents pools at an elevated temperature (42° C) could increase the rate of multiplication of Salmonella Enteritidis sufficiently to support the detection of contamination by a rapid lateral flow immunodiffusion method within a single day. Pools of 10 eggs were contaminated with approximately 10 CFU of Salmonella Enteritidis , supplemented with concentrated broth enrichment medium, and incubated at either 37° C or 42° C. Incubation of contaminated egg pools at 42° C resulted in significantly higher Salmonella Enteritidis levels after 6, 8, 10, and 12 hours. However, incubation at 42° C could only generate a mean log Salmonella Enteritidis concentration of 4.21 CFU/ml within a single working day (8 hours), inadequate to support efficient detection by most rapid assays. Accordingly, detection of Salmonella Enteritidis contamination in egg pools by a rapid lateral flow immunodiffusion test was not achieved at a high frequency until 12 hours of incubation at 42° C.