Leafy vegetables are the foods second most commonly associated with outbreaks of foodborne illness in the United States, most notably when contaminated with Escherichia coli O157:H7.
 Now Maria Brandl and colleagues of the Agricultural Research Service, USDA, Albany, Calif., show via transcriptome analysis that O157:H7 undergoes a variety of stresses within the chemical environment of lettuce cells broken during cutting and packaging. They show further that the pathogen adapts to these stressors, including oxidation, which "may partly explain why chlorine has been ineffective in sanitizing fresh-cut produce," says Brandl. Her study, she notes, is the first to map the microbe's physiological response to this environment, and "its weaknesses can now be exploited to design new, multifaceted approaches to decontamination. Surprisingly, we also observed in lettuce lysates that the pathogen upregulated its arsenal to cause disease in the human host." The findings suggest that in contaminated lettuce, even fewer cells may be necessary to sicken humans. "We are actively pursuing this line of research to gain a better understanding of the epidemiology in association with fresh produce." (J. L. Kyle, C. T. Parker, D. Goudeau, and M. T. Brandl. 2010. Transcriptome analysis of Escherichia coli O157: H7 exposed to lysates of lettuce leaves. Appl. Environ. Microbiol. 76:1375-1387.)
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