Mutant 6137 of Salmonella enterica serovar Typhimurium has a transposon inserted in the putative transporter gene yjeH and shows a more-than-fourfold reduction in resistance to ceftriaxone. In this report we have used proteomic analysis to compare outer membrane protein profiles between this mutant and its parental strain R200. Five identified proteins were found to be altered. Of these proteins, the level of expression of the porin OmpD was increased and those of the putative outer membrane proteins STM1530 and STM3031, a subunit of the proton-pumping oxidoreductase NuoB and the heat shock protein MopA were decreased in 6137 strain. Although the function of the yjeH gene remains unknown, a complementation assay suggested that the OmpD, STM1530, STM3031, NuoB, and MopA proteins are associated with ceftriaxone resistance and the expression of these proteins is influenced by the putative transporter gene yjeH in S. enterica serovar Typhimurium. (c) 2007 Elsevier Inc. All rights reserved.