ABSTRACT
@#Abstract：Objective To investigate the feasibility of outer membrane protein C（OmpC）as a protein presenting platform targeting antigen to the surface of outer membrane vesicle（OMV）. Methods The recombinant expression plasmid containing ompC gene fragment and Staphylococcus aureus EsxA antigen gene（esxA gene）was constructed，transformed to competent E. coli BL21（DE3），inducedbyIPTG，andanalyzedforexpressedproductby 12%SDS⁃PAGE. Thetotalproteinofrecombinant strain OMV was analyzed by 12% SDS⁃PAGE，and the localization of fusion protein on the surface of OMV was detected by Western blot and Flow NanoAnalyzer. Results The recombinant expression plasmid containing ompC gene and esxA gene was constructed correctly as proved by sequencing. 12% SDS⁃PAGE showed that the fusion protein OmpC⁃EsxA had a relative molecular mass of about 57 000，which was consistent with the expected size，while the total protein of OMV showed multiple target protein bands，indicating that recombinant strain OMV was successfully extracted. The fusion protein OmpC⁃ EsxA on the surface of recombinant strain OMV specifically bound to mouse antibody against His⁃Tag，and OMVs labeled with fluorescent antibody were detected by Flow NanoAnalyzer. Conclusion OmpC may be used as a protein presenting plat⁃ form to locate antigen to OMV surface，which was expected to be applied in the development of antigen presentation vaccine. Keywords：Outer membrane protein C（OmpC）；Protein presentation；Outer membrane vesicle（OMV）
ABSTRACT
Salmonella enterica serovar Typhimurium is one of the most important bacterial pathogens causing diarrhea. The resistance of S. typhimurium to antimicrobial agents, which has recently been isolated from patients, is causing serious problems. We investigated the effects of salicylic acid (Sal) and acetyl salicylate (AcSal) on the susceptibility of S. typhimurium to cephalosporin antibiotics, which are known to increase resistance to cephalosporin and quinolone antibiotics. The MIC of cephalosporin antibiotics was higher than that of the media without Sal. The rate of accumulation of ethidium bromide (EtBr) in the bacteria by the outer membrane protein (Omp) was not different from that of the bacteria cultured in the medium containing Sal. However, Carbonyl cyanide-m-chlorophenylhydrazone (CCCP), an inhibitor of bacterial efflux pumps, significantly reduced the rate of accumulation of EtBr in bacteria cultured on Sal containing medium. In the medium containing CCCP, the MIC of the antimicrobial agent tended to decrease as compared with the control. In addition, the MIC of the bacteria treated with CCCP and Sal was higher than that of the antimicrobial agent against the CCCP treated experimental bacteria. These results suggest that Sal decreases the expression of OmpF in the Omp of S. typhimurium and reduces the permeability of cephalosporin antibiotics to bacteria, which may induce tolerance to cephalosporin antibiotics.