Food Poisoning Law Blog

Contrary to what most people would think, young (inner) lettuce greens may pose a greater risk of E. coli O157:H7 contamination than older (middle) leaves, according to a study conducted by researchers at Produce Safety and Microbiology Research Unity, Albany, California and the University of California, Berkeley. The study found that E. coli O157:H7 consistently colonized on young (inner) romaine lettuce leaves at a rate ten-times greater than on the middle leaves of the romaine lettuce. The reason may be nitrogen content. Young-leaf exudates used in the study were found to have about 2.9 times more nitrogen than the middle-leaf exudates. 

According to the researchers involved in this study, “Our results indicate that leaf age and nitrogen content contribute to shaping the bacterial communities of preharvest and post-harvest lettuce and that young lettuce leaves may be associated with a greater risk of contamination with E. coli O157:H7.”

Reference: M.T. Brandl, R. Amundson. 2008. Leaf age as a risk factor in contamination of lettuce with Escherichia coli O157:H7 and Salmonella enterica. Applied and Environmental Microbiology, 74. 8: 2298-2306.