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eggs are sterile at the time of oviposition or harbor
very few microorganisms. Contamination of the shell
occurs afterwards. Eggs
possess several natural barriers that prevent bacterial invasion
including the shell, membranes, and antibacterial factors
present in the egg white. Bacterial contamination can
occur through improper washing, e.g., using a wash solution
at a temperature less than the temperature of the egg or
a wash solution with a high iron content (excess iron overcomes
the ability of the conalbumin to inhibit bacterial growth). Eggs
are usually spoiled by gram-negative bacteria such us Pseudomonas,
Serratia, Proteus, Alcaligenes, and Citrobacter. Good
sanitation practices are essential.
Salmonella is the principal
pathogen currently associated with eggs and egg products. Beginning
in the late 1980's, the incidence of human S. enteritidis infections
began to increase dramatically in the United States. Outbreaks
have been associated with clean, intact, Grade A shell eggs. This
serotype of Salmonella can colonize the reproductive
organs in laying hens leading to internal contamination of
eggs before oviposition. Most egg-associated S.
enteritidis outbreaks
have also involved temperature abuse that allowed the pathogen
to multiply to more dangerous levels.
Recommended tests:
Aerobic Plate Count (should
be <10
per g).
Salmonella test.
Additional tests:
Total Coliforms.
Yeast and Mold Count.
Liquid, frozen, and dried egg
products are usually pasteurized and, thus, the
likelihood of finding Salmonella in a pasteurized
product is very low. However, products can be recontaminated
after pasteurization. This is also the case with Listeria
monocytogenes. Good sanitation practices are very
important. Indicators of lack of sanitation are the
coliform group and E. coli.
Recommended tests:
Aerobic Plate Count (should
be <25,000
per g).
Salmonella test.
Listeria test.
Additional tests:
Total Coliforms and E. coli (should
be <10 per g).
Yeast and Mold Count (should be <10 per g).
Adapted from:
Ricke, S. C., Birkhold, S. G.,
and Gast, R. K. 2001. Eggs and Egg Products, p.
473. In F. P. Downes and K. Ito (eds.), Compendium of
Methods for the Microbiological Examination of Foods. American
Public Health Association, Washington, DC.
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