Metagenomic Characterization of Bacterial Communities on Ready-to-Eat Vegetables and Effects of Household Washing on their Diversity and Composition.

Soultana Tatsika,Savvas Genitsaris,Hera Karayanni,Katerina Karamanoli

doi:10.3390/pathogens8010037

Abstract

Ready-to-eat (RTE) leafy salad vegetables are considered foods that can be consumed immediately at the point of sale without further treatment. The aim of the study was to investigate the bacterial community composition of RTE salads at the point of consumption and the changes in bacterial diversity and composition associated with different household washing treatments. The bacterial microbiomes of rocket and spinach leaves were examined by means of 16S rRNA gene high-throughput sequencing. Overall, 886 Operational Taxonomic Units (OTUs) were detected in the salads’ leaves. Proteobacteria was the most diverse high-level taxonomic group followed by Bacteroidetes and Firmicutes. Although they were processed at the same production facilities, rocket showed different bacterial community composition than spinach salads, mainly attributed to the different contributions of Proteobacteria and Bacteroidetes to the total OTU number. The tested household decontamination treatments proved inefficient in changing the bacterial community composition in both RTE salads. Furthermore, storage duration of the salads at refrigeration temperatures affected the microbiome, by decreasing the bacterial richness and promoting the dominance of psychrotropic bacteria. Finally, both salads were found to be a reservoir of opportunistic human pathogens, while washing methods usually applied at home proved to be inefficient in their removal.

Highlights

Plant associated bacteria have gained attention in recent years due to the potential relationships to human health in terms of the spread of foodborne pathogens and the contribution of edible plant diversity to human gut microbiomes [1,2]
The aim of the current study was to determine the bacterial community composition of two different RTE leafy salads at the point of consumption and to investigate the changes in bacterial diversity and composition associated with different household washing treatments and different storage periods, using 16S rRNA gene high-throughput sequencing (HTS) methods
High-throughput 16S rRNA gene amplicon sequencing was used to characterize the bacterial community composition associated with RTE leafy salads at the point of consumption

Summary

Introduction

Plant associated bacteria have gained attention in recent years due to the potential relationships to human health in terms of the spread of foodborne pathogens and the contribution of edible plant diversity to human gut microbiomes [1,2]. Ready-to-eat (RTE) leafy vegetables are minimally processed products considered as foods that can be consumed immediately at the point of sale without further preparation or treatment. They are colonized by a variety of bacteria and recent outbreaks of human disease. Pathogens 2019, 8, 37 associated with fresh products have shown their vulnerability to colonization by foodborne pathogens such as Escherichia coli O157:H7 and Salmonella enterica [6,7]. European legislation is posing several microbiological criteria as indexes of the hygienic process and safety, proposing that the recovery of E. coli in RTE vegetables is an index of the hygienic process under which they are produced, and the recovery of Salmonella spp. and Listeria monocytogenes is an index of safety

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