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Adaptation of Commensal Escherichia coli in Tomato Fruits: Motility, Stress, Virulence

A. Vassallo,R. Amoriello,Prandvera Guri,Lorenzo Casbarra,M. Ramazzotti,M. Zaccaroni,C. Ballerini,D. Cavalieri,M. Marvasi

Published 2023 in Biology

ABSTRACT

Simple Summary When pathogenic bacteria contaminate food, they can harm humans, causing, for example, gastrointestinal disorders. This is a main concern, especially in the case of foods that are consumed fresh and/or are not cooked following common hygiene standards. Thus, it is important to understand how bacteria can survive and prosper once they have contaminated fruits and vegetables, regardless of the presence of defense mechanisms in these plant tissues. In this work, we investigated the ability of a harmless E. coli strain’s ability to adapt to a tomato’s external portion, where bacteria encounter harsh growth conditions. E. coli grown in tomatoes was isolated and compared with E. coli grown in standard laboratory conditions: this comparison allowed us to identify potential molecular determinants helping E. coli to survive in tomatoes. This investigation was conducted through sequencing of DNA and through assays proving that growth in tomatoes altered, at least in part, some features of this bacterium, such as its ability to withstand chemical compounds. Abstract Food contamination can be a serious concern for public health because it can be related to the severe spreading of pathogens. This is a main issue, especially in the case of fresh fruits and vegetables; indeed, they have often been associated with gastrointestinal outbreak events, due to contamination with pathogenic bacteria. However, little is known about the physiological adaptation and bacterial response to stresses encountered in the host plant. Thus, this work aimed to investigate the adaptation of a commensal E. coli strain while growing in tomato pericarp. Pre-adapted and non-adapted cells were compared and used to contaminate tomatoes, demonstrating that pre-adaptation boosted cell proliferation. DNA extracted from pre-adapted and non-adapted cells was sequenced, and their methylation profiles were compared. Hence, genes involved in cell adhesion and resistance against toxic compounds were identified as genes involved in adaptation, and their expression was compared in these two experimental conditions. Finally, pre-adapted and non-adapted E. coli were tested for their ability to resist the presence of toxic compounds, demonstrating that adaptation exerted a protective effect. In conclusion, this work provides new information about the physiological adaptation of bacteria colonizing the tomato fruit pericarp.

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