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ABSTRACTOuter membrane proteins (OMPs) serve as the permeability channels for nutrients, toxins, and antibiotics. In Escherichia coli, OmpA has been shown to be involved in bacterial virulence, and OmpC is related to multidrug resistance. However, it is unclear whether OmpC also has a role in the virulence of E. coli. The aims of this study were to characterize the role of OmpC in antimicrobial resistance and bacterial virulence in E. coli. The ompCdeletion mutant showed significantly decreased susceptibility to carbapenems and cefepime. To investigate the survival of E. coliexposed to the innate immune system, a human blood bactericidal assay showed that the ompCmutant increased survival in blood and serum but not in complement-inactivated serum. These effects were also demonstrated in the natural selection of OmpC mutants. Also, C1q interacted with E. colithrough a complex of antibodies bound to OmpC as a major target. Bacterial survival was increased in the wild-type strain in a dose-dependent manner by adding free recombinant OmpC protein or anti-C1q antibody to human serum. These results demonstrated that the interaction of OmpC-specific antibody and C1q was the key step in initiating the antibody-dependent classical pathway for the clearance of OmpC-expressing E. coli. Anti-OmpC antibody was detected in human sera, indicating that OmpC is an immunogen. These data indicate that the loss of OmpC in E. coliis resistant to not only antibiotics, but also the serum bactericidal effect, which is mediated from the C1q and anti-OmpC antibody-dependent classical pathway.

ABSTRACTHelicobacter pyloriis a Gram-negative, spiral-shaped bacterium that infects more than 50% of the human population and can cause gastritis, peptic ulcer, or gastric malignancies. It is generally viewed as an extracellular microorganism. In a gentamicin protection assay on AGS or MKN45 cells, H. pyloricould invade the epithelial cells and multiply within double-layer vesicles either on the plasma membrane or in the cytoplasm. A 5-fold increase in the number of bacteria was recultured from the infected cells at 12 h, compared with the number of invading cells at 2.5 h postinfection. The autophagic vesicles induced by H. pyloriare the sites of replication and also of the degradation of the replicating bacteria after fusion with lysosomes. Many H. pyloribacteria in coccoid form associated with the plasma membrane can be released into culture. Only cell-penetrating antibiotics can enhance the intracellular killing of the replicating bacteria. The multiplication of H. pyloriwithin cells provides a niche for its resistance to antibacterial therapy and has a significant impact on its biological life cycle.

ABSTRACTLewis X (Lex) antigen is expressed on the human gastric mucosa and the O-specific chain of lipopolysaccharides of Helicobacter pylori. This antigen can induce autoantibodies, which may be involved in bacterial colonization and thus deserve further investigation. Flow cytometry was used to examine the effects of anti-Le monoclonal antibodies (MAbs) on H. pyloriadhesion. A babA2mutant was also constructed to evaluate the effect of an anti-LexMAb on adhesion. The bacterial agglutination and in situ adhesion assays were used to confirm the anti-LexMAb effect on H. pyloriadhesion. This study revealed that an anti-LexMAb, but not an anti-LebMAb or an anti-LeyMAb, could enhance the adhesion of H. pyloristrains that expressed high levels of Lexantigen to AGS cells. The enhancement was not found on an H. pyloristrain with a low level of Lexantigen. Anti-LexMAb could increase the adhesion of both the wild-type strain and its isogenic babA2mutant to AGS cells. When AGS cells were pretreated with anti-LexMAb, the adhesion of the babA2mutant also increased. Only anti-LexMAb could promote bacterial agglutination, and the in situ adhesion assay further confirmed that adding anti-LexMAb resulted in denser bacterial adhesion on the gastric epithelia collected from clinical patients. These results suggest anti-LexMAb could specifically enhance the adhesion abilities of H. pyloristrains through a mechanism by which anti-LexMAb promotes bacterial aggregation and mediates bivalent interaction (antigen-antibody-antigen) between bacteria and host cells.