UMPS and infection: Such as OmpD in S. Enteritidis is nearly identical to the S. Typhimurium and differs only by a single amino acid, which is located on the outer membrane and exists as a trimer to generate a tunnel aperture size that allows a single Fab to cross the LPS channel and bind to the bacterial surface.17 Although only one Fab can access the LPS channel created by certain trimeric proteins in the surrounding LPS layer, it is also able to confer protection against infection of Salmonella.