Commercially prepared mayonnaise may offer some slight protection against food poisoning. Studies conducted nearly 30 years ago at the University of Wisconsin's Food Research Institute in Madison found that the high acid content of commercially prepared mayonnaise, not the variety made at home with fresh eggs, killed strains of salmonella and staphylococcus bacteria. In the 1980s, the University of Georgia's Center for Food Safety and Quality found that the acid in commercial mayonnaise made it lethal to salmonella and Listeria. The bacteria failed to grow in either type of mayonnaise. Recipes that use uncooked eggs are what tainted mayonnaise's reputation.
Raw eggs are a common source of salmonella.
An investigation showed that raw eggs had been used to make mayonnaise for patients on low-sodium diets. While most patients received commercially prepared mayonnaise, all batches of salad became contaminated by utensils that were used to mix the salads. Nine people died. But just because commercially prepared mayonnaise has a good track record for killing common bacteria does not mean that it can be used without taking the proper precautions. Wash your hands with water and soap, especially before food preparation.