This is a family of archaeal and bacterial proteins predicted to be periplasmic. YdeI is important for resistance to polymyxin B in broth and for bacterial survival in mice upon oral, but not intraperitoneal inoculation, suggesting a role for YdeI in the gastrointestinal tract of mice [1]. Production of the ydeI gene is regulated by the Rcs (regulator of capsule synthesis) phospho-relay system pathway independently of RcsA, and additionally transcription of the protein is regulated by the stationary-phase sigma factor, RpoS (sigma-S) [1]. YdeI confers protection against cationic AMPs (Antimicrobial peptides) or bacteriocins in conjunction with the general porin Omp, thus justifying its name of OmdA, for OmpD-Associated protein [2].

1: The Rcs phosphorelay system is specific to enteric pathogens/commensals and activates ydeI, a gene important for persistent Salmonella infection of mice. Erickson KD, Detweiler CS; Mol Microbiol. 2006;62:883-894. PMID:17010160

2: A protein important for antimicrobial peptide resistance, YdeI/OmdA, is in the periplasm and interacts with OmpD/NmpC. Pilonieta MC, Erickson KD, Ernst RK, Detweiler CS; J Bacteriol. 2009;191:7243-7252. PMID:19767429