Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 30, 1997
Publication Date: N/A
Interpretive Summary: Quality assurance programs for reducing egg-associated transmission of Salmonella enteritidis (SE) to humans often rely on culturing pools of egg contents to detect infected laying flocks. After egg contents are pooled together for sampling, they are often incubated to allow small numbers of SE cells to multiply to easily detectable levels. The direct plating method for culturing eggs relies on this incubation step to increase SE levels so that a sample of each pool can be transferred directly to agar culture media for detection of SE (without any additional enrichment steps). Direct plating is simple and rapid, but may not detect very small numbers of SE. The present study evaluated the effectiveness of adding highly concentrated broth enrichment media to incubating egg pools for promoting SE growth and thereby supporting detection by direct plating. Adding tryptone soya broth, at concentrations of 5 times normal strength or more, led to a significant improvement in the recovery of SE cells added experimentally to egg pools in very small numbers. This method thus enables detection of contaminating SE cells in eggs to be accomplished rapidly and effectively.
Technical Abstract: Culturing egg contents to detect Salmonella enteritidis (SE) is an important tool for identifying infected laying flocks in programs for reducing the transmission of SE to humans by contaminated eggs. A relatively rapid and inexpensive (but comparatively insensitive) culturing protocol allows pools of eggs to incubate to promote the expansion of low contaminant levels, followed by direct plating on selective agar to detec SE. The present study evaluated the efficacy of supplementing incubating egg pools with highly concentrated selective and non-selective enrichment broth media for rapidly and efficiently recovering SE. When pools of liquid whole egg were contaminated with fewer than 10 SE cells each, both iron and concentrated media supplementation improved SE recovery. Supplementation with concentrated tryptone soya broth resulted in significantly better SE recovery than iron supplementation. Highly efficient presumptive detection of very low incidences and levels of SE contamination by direct plating was accomplished in a total of 48 hours by adding 5X tryptone soya broth to incubating egg pools.