Lettuce Salad as a Carrier of Microorganisms of Public Health Significance 1.
Culture, distribution, and preparation of lettuce for salad offers opportunities for contamination with and growth of microorganisms. Protection and preservation methods, even when appropriate, may likewise be favorable for the contaminants. Fresh lettuce, as commercially available, was studied to determine the magnitude of contamination and the nature of representative contaminants. Specific contaminants of public health interest were added to test portions to determine their fate during storage of lettuce as a salad at room temperature. Storage of lettuce in bowls on ice resulted in very little cooling of most of the lettuce. Microbial plate counts on fresh lettuce commonly were over 105/g and the diversity of the microflora indicated a generally favorable microenvironment for many types of bacteria. Inocula of Salmonella typhimurium , Escherichia coli , and Staphylococcus aureus fared well on lettuce salad and were able to grow at room temperature storage. Commmercial "whitener" added to lettuce to preserve freshness reduced the total microflora and indicator organisms of public health significance.