Precut salad may encourage growth of Salmonella

https://www.eurekalert.org/pub_releases/2016-11/asfm-psm111616.php

Public Release: 18-Nov-2016
Precut salad may encourage growth of Salmonella
American Society for Microbiology

A new study from the University of Leicester shows that small amounts of damage to salad leaves in bagged salads encourage the presence of Salmonella enterica. Juices released from damaged leaves also enhance the pathogen's ability to attach to the salad's plastic container. The research is published November 18th in Applied and Environmental Microbiology, a journal of the American Society for Microbiology.

In the study, salad juices in water--to mimic the grocery salad bag environment--more than doubled motility, or movement of individual Salmonella bacteria, abetting salad leaf colonization. In the course of a typical five day refrigeration storage time around 100 Salmonella bacteria multiplied to approximately 100,000 individual bacteria. Salad juices also boosted formation of biofilms on salad leaves. Microbial biofilms generally cling tenaciously to the surfaces they coat--medical implants, stainless steel, or one's teeth, in the form of dental plaque--and Salmonella biofilms on salad leaves are no exception. They are powerfully resistant to being washed off.

Yet surprisingly, the normal microbial flora on salad leaves did not respond to leaf juices, suggesting that the leaf juices give Salmonella a marked advantage in colonizing salad leaves as compared to competing bacteria, according to the report.

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