UMPS and infection: This could reflect higher stringency of our model (challenge infection with virulent Salmonella vs. highly attenuated mutant Salmonella), denatured three-dimensional structures of our recombinant antigen preparations vs. native antigens, and/or presence of undetected minor protective antigens (such as IroN and CirA) besides OmpC, OmpD, and OmpF in the previously used outer membrane antigen preparations.