Novel pESI-encoded autotransporter adhesin PeaP of epidemic Salmonella strains mediates adhesion, atypical biofilm formation, and poultry colonization

Abstract

Salmonella enterica serovar Infantis (SIN) has rapidly become the dominant serovar in poultry worldwide, a success largely linked to the acquisition of the 285 kb megaplasmid pESI. While pESI-encoded antibiotic-resistance and iron-uptake systems are well characterized, pESI-mediated adhesion mechanisms remain poorly understood. Here we identify a novel pESI-encoded monomeric autotransporter adhesin, designated PeaP (pESI-encoded autotransporter protein), and demonstrate its pivotal role in atypical biofilm formation, interference with motility, and colonization of the chicken host. Biofilm assays revealed that pESI-harboring strain SIN 119944 forms robust biofilms at 37 {degrees}C and 42 {degrees}C, temperatures at which CsgD-dependent biofilm formation is negligible. Deletion of csgD did not impair this phenotype, whereas deletion of peaP abolished high-temperature biofilm development and restored motility to wild-type levels. Proteomic profiling of sessile versus planktonic cells highlighted PeaP as the most abundant pESI-derived protein in the biofilm fraction. AlphaFold-based modelling and negative-stain transmission electron microscopy showed that PeaP comprises a C-terminal {beta}-barrel and a 1,500 aa passenger domain with three tandem repeats, projecting filamentous appendages [~]37-nm from the outer membrane. Antibody blockade of PeaP reduced surface adhesion >6-fold, confirming its adhesive function. In an infection model of 2 day-old chicken, the peaP mutant displayed significantly lower colonization, indicating PeaP-mediated adhesion in vivo. Collectively, pESI-positive SIN deploys PeaP for CsgD-independent, temperature-tolerant biofilm formation and enhanced gastrointestinal colonization, providing a mechanistic basis for the epidemic spread of this multidrug-resistant pathogen in poultry.