It is not uncommon to directly correlate the consumption of
salads with a healthy lifestyle. That is why it may come as a surprise to many
that salads are now ranked as the second most common source of outbreaks of
food borne illness. This is because salad leaves, particularly lettuce and
spinach, have a high probability of being infected by enteric pathogens due to
their minimal processing, raw ingestion, and high-water content. A research
carried out by Koukkidis and colleagues showed that there is a significant
increase in the probability of bagged salad leaves acquiring Salmonella. This occurs as the lettuce leaves become physically
damaged and release juices. These juices are what allow Salmonella to grow,
colonize, and linger in the salad leaves. Even though the growth of Salmonella
was higher at non-refrigeration temperatures, leaves that were refrigerated over
five days also displayed growth. Next time you reach for your bagged salad leaves,
be aware that they may pose a serious infection risk.
Panels A and B show typical pictures of a salad microbiota. Panel C displays light microscopy images of salmonella of salad bag plastic in water in the absence and presence of spinach juice. Panel D shows blue light microscopy of salmonella incubated in water in the presence and absence of spinach juice. Figure from Koukkidis et al. 2017
Original article:
Original article:
Koukkidis G, Haigh R, Allcock N, Jordan S, Freestone P. 2017. Salad leaf juices enhance Salmonella growth, colonization of fresh produce, and virulence. Appl Environ Microbiol 83:e02416-16
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