Introduction An overwhelming majority of eggs contain no bacteriological contamination. As described in the section on Egg Quality, the intact eggshell and the albumen provide a very secure barrier to microbiological invasion. However, a very limited range of bacteria can enter the egg directly from the body of the hen. One of these, Salmonella pullorum, is highly pathogenic to newly hatched chicks (though not to humans) and has been eradicated from all commercial chicken populations. This eradication process was accomplished many years ago and very few outbreaks of S. Pullorum are reported today. All of the breeding stock sold by ISA are free of Salmonella at the time of shipping. Salmonella enteritidis Salmonella enteritidis (SE) began to appear in the yolks of intact shell eggs in the 1980's and created significant problems for the egg industry. SE bacteria, if ingested in large numbers, can cause serious illness in humans who consume contaminated eggs. The SE infection is picked up by the laying hen from the environment. It is seldom pathogenic for the hen. SE migrates eventually to the ovary and is deposited on the surface of developing ova. Not every egg is contaminated. The infection is located outside the vitelline membrane and so multiplication may be limited by antibacterial proteins in the egg white. If the egg undergoes prolonged storage and the yolk membrane begins to deteriorate, bacterial multiplication can accelerate as the organisms come in contact with yolk material. In eggs that have been broken open prior to cooking, and the contents mixed, bacterial multiplication occurs extremely fast, the rate dependent on temperature. Uncooked or under-cooked food like mayonnaise, custard, etc may still contain viable bacteria which continue to multiply unless the food is refrigerated. Control of SE is by eliminating it as far as possible from the environment of the laying hens. This is accomplished by rigorous testing of environmental samples and by stringent anti-microbial treatment of layer facilities found to be positive for SE. Vaccination of laying flocks is also used to limit infection and/or spread of SE. Other Salmonella A variety of other Salmonella serotypes that occur in the layers' environment can occasionally create public health challenges. These bacteria may contaminate the egg shell surface and eventually reach the consumer. Risk of such an event is greatly reduced if eggs are properly washed during the grading process. In jurisdictions where eggs are not washed, the bacteria may remain on the eggshell surface and cross-contaminate other foods during meal preparation. Other bacteria While all kinds of micro organisms will undoubtedly exist in the layers' environment, they are unlikely to contaminate eggs because of the defence mechanisms described elsewhere in this document. Food safety issues with eggs Most egg dishes involve only partly cooking the eggs; some, for example, mayonnaise, use raw eggs. Seldom is the cooking process sufficient to kill bacteria. Fried or scrambled eggs, omelettes etc. fall into this category. This raises serious food safety issues even though the eggs themselves may be uncontaminated. Once eggs are removed from the shell, they may be easily cross-contaminated from bacteria in the environment, for example from other foods being prepared at the same time. Regardless of the source of bacteria, it must be remembered that at room temperature, bacterial numbers double every twenty minutes. Therefore it is important to consume cooked egg dishes immediately. Do not allow them to stand at room temperature or under a heat lamp for more than a few minutes prior to eating them. With raw egg products like mayonnaise, keep them refrigerated when not in use. |