Differences in the multiplication of Salmonella enteritidis strains in liquid whole egg: implications for detecting contaminated eggs from commercial laying flocks.

Bacterial culturing of eggs for Salmonella enteritidis has become an important tool in efforts to identify laying flocks that potentially threaten public health. As pools of egg contents are generally incubated before culturing to allow S. enteritidis numbers to multiply to easily detectable levels, any differences in the multiplication of S. enteritidis strains in egg pools could result in similar differences in the likelihood of detection. To assess whether 12 S. enteritidis strains would multiply to reach different final levels in pools of egg contents, 100-mL samples of liquid whole egg were experimentally contaminated with < 10 cfu of the various strains. After incubation for 24 h at 37 C, the number of colony-forming units of S. enteritidis in each pool was determined. Significant differences were observed between strains in the extent of expansion of the S. enteritidis population during incubation (some strains grew to levels more than a thousand times greater than others). Iron supplementation of the pools during incubation significantly increased S. enteritidis growth and reduced the extent of variation between strains.