Ready-to-eat rocket salads as potential reservoir of bacteria for the human microbiome

Reportedly, Western-type diets may induce the loss of key microbial taxa within the gastrointestinal microbiota, promoting the onset of non-communicable diseases. It was hypothesized that the consumption of raw vegetables could contribute to the maintenance of the intestinal microbial community structure. To test this hypothesis, viable plate count and metataxonomics were used to explore the bacteria associated to commercial rocket salads produced through different farming practices: traditional (conventional, organic, and integrated) and vertical farming. Rocket salad from vertical farming had much lower viable bacteria and had a bacterial community structure markedly different from that of rocket salads from traditional farming. Furthermore, although alpha- and beta-diversity analyses did not differentiate rocket samples according to the farming techniques, several bacterial taxa distinguished organic and integrated from conventional farming salads, suggesting that the farming practice could affect the taxonomic composition of rocket bacterial communities. Lactic acid bacteria (LAB) were isolated only from rocket salads from traditional farming, and predominantly belonged to the genus Leuconostoc (60% of isolates). Furthermore, viable rocket-associated LAB belonged to different species, which were variably distributed among samples and could be partly associated to farming practices. Finally, experiments of simulated gastrointestinal digestion revealed that several taxonomically different rocket-associated bacteria could survive the gastrointestinal transit, and that such ability is particularly enhanced for LAB. This study suggests that commercial ready-to-eat rocket salad harbors live bacteria that, once ingested, possess the ability to survive the gastrointestinal transit potentially contributing to the bacterial taxonomic structure of the human gut microbiota.