Downy mildew is usually a lettuce grower’s worst nightmare; it’s the biggest problem in lettuce production. Multiple applications of protectants are usually needed to control the fungus-like water mold Bremia lactucae that causes downy mildew, and it may cost millions of dollars more in bad years when it can wipe out entire crops regardless of treatment.
But ARS microbiologist Maria Brandl at the Produce Safety and Microbiology Research Unit in Albany, California, is more interested in another pathogen that sometimes can be traced to lettuce fields: Escherichia coli O157:H7. This highly virulent bacterium is one of the most common causes of foodborne illness in people. While food sources of E. coli O157:H7 are as diverse as undercooked beef, sprouts, raw dairy, shelled walnuts, fruits, and vegetables, multi-state outbreaks have been traced back to lettuce.
How this pathogenic bacterium gets ensconced on lettuce plants has been a persistent mystery. Various possible pathways have been investigated, from wandering feral pigs to contaminated irrigation water to the feces of snails, flies, and flying birds.
To read the rest of the story, please go to: USDA AgResearch Magazine
