E. coli- fresh produce interactions

<p dir="ltr">Fresh produce such as leafy green vegetables and ready-to-eat salads are an essential part of a healthy human diet. However, they have recently become associated with food- borne illness outbreaks by bacteria such as E. coli. Further, enteric pathogen contamination of non-cooked fresh produce such as lettuce and spinach is also becoming recognized as a food safety problem of economic importance. Therefore, the aim of this project was to investigate whether juice released from salad leaf tissues during damage caused by commercial salad processing affected E. coli growth, virulence and its ability to colonize fresh salad produce and cause infection of host cells. E. coli responsiveness to salad juices was analyzed in water, which reflects the watery environments inside salad bags, and in host-like serum media (to mimic the consumption of contaminated salad leaves). The effect of lettuce and spinach extract on E. coli growth, biofilm formation and virulence were investigated. Experiments showed that E. coli recognized and strongly responded to juices released from salad leaves. Lettuce and spinach leaf juices at less than 0.5% v/v stimulated E. coli growth in water and serum media over controls by more than 1000-fold, due to the provision of iron from transferrin in serum. Salad leaf juices also induced E. coli to produce a more extensive biofilm and caused marked changes in gene expression, as shown by proteomics studies. Salad leaf extract exposure also enhanced the virulence of E. coli infecting Galleria mellonella. Further impact of salad extract exposure on E. coli virulence represented an enhancement of its ability to adhere to and invade a Caco-2 cell line. Exposure to salad extract increased salad leaf colonization by E. coli.</p><p dir="ltr">Collectively, this work suggests that measures to prevent enteric pathogen contamination of fresh produce must be considered a food safety priority.</p>