Systematic analyses of factors required for adhesion ofSalmonella entericaserovar Typhimurium to corn salad (Valerianella locusta)

Abstract

27Salmonella enterica is a foodborne pathogen leading to gastroenteritis and is commonly 28 acquired by consumption of contaminated food of animal origin. However, numbers of 29 outbreaks linked to the consumption of fresh or minimally processed food of non-animal origin 30 are increasing. New infection routes of S. enterica by vegetables, fruits, nuts and herbs have to 31 be considered. This leads to special interest in S. enterica interactions with leafy products, e.g. 32 salads, that are consumed unprocessed. The attachment of S. enterica to salad is a crucial step 33 in contamination, but little is known about the bacterial factors required and mechanisms of 34 adhesion. S. enterica possesses a complex set of adhesive structures whose functions are only 35 partly understood. Potentially, S. enterica may deploy multiple adhesive strategies for adhering 36 to various salad species, and other vegetables. Here, we systematically analyzed the 37 contribution of the complete adhesiome, of LPS, and of flagella-mediated motility of S. enterica 38 serovar Typhimurium (STM) in adhesion to corn salad. We deployed a reductionist, synthetic 39 approach to identify factors involved in the surface binding of STM to leaves of corn salad with 40 particular regard to the expression of all known adhesive structures using the Tet-on system. 41 This work reveals the contribution of Saf fimbriae, type 1 secretion system-secreted BapA, an 42 intact LPS, and flagella-mediated motility of STM in adhesion to corn salad leaves. 43 44 Importance 45 Human gastrointestinal pathogens are often transmitted by animal products, but recent 46 outbreaks show increasing importance of vegetables as source of infection by pathogenic E. 47 coli or Salmonella enterica. The mechanisms of binding of S. enterica to vegetables such as 48 salad are only poorly understood. We established an experimental model system to 49 systematically investigate the role of adhesive structures of S. enterica serovar Typhimurium 50 in binding to corn salad leaves. The contributions of all members of the complex adhesiome, 51 24.11.2019S. Typhimurium adhesion to corn salad 3 flagella, and O-antigen were evaluated. We identified that Saf fimbriae, type 1 secretion system-52 secreted BapA, an intact LPS, and flagella-mediated motility contribute to adhesion of 53 Salmonella to corn salad leaves. These results will enable future investigations on factors 54 contributing to contamination of vegetables under agricultural conditions. 55 56 24.11.2019 S. Typhimurium adhesion to corn salad Furthermore, SR11 ∆12 strains with additional deletions of single adhesive structures showed 131 no altered levels of adhesion compared to SR11 ∆12, except for deletion of Salmonella 132 157