The rabbit enteropathogenic E. coli (rEPEC) strain RDEC-1 possesses a lifA homologue adjacent to the LEE pathogenicity island. To study the entire nucleotide sequence and biological function of lifA,the DNA sequence and biological function of RDEC-1 lifA were analysed with gene cloning,gene knock-out and in vivo virulence examination. The result showed that the entire coding sequence of the lifA of RDEC-1 shares nearly absolute homology with the lifA of human isolates. RDEC-1 lifA inhibited IL-2 expression in stimulated rabbit peripheral blood mononuclear cells. We further demonstrated significant reduction in fecal bacterial shedding by RDEC-1 derivative lifA mutant when compared with its parent strain. In a competitive study when rabbits were inoculated with a combination of the WT and the mutant, the WT was the predominant bacteria recovered from fecal samples, while fewer mutant bacteria were recovered. However,the lifA mutant is able to induce A/E type of lesions as efficient as the parent strain. The data provide direct evidence that lifA of rEPEC plays a role in immunomodulation and in in vivo colonization in the intestinal tract.

AIM: To express chimeric toxin Stx2a’-LHRH a nd to investigate the cytotoxic activity of recombinant toxin Stx2a’-LHRH to huma n carcinoma cells.METHODS: Stx2a’-LHRH sequences that added the res tri ction endonucleases NcoⅠ and EcoRⅠ at the 5' and 3 ends were amplified by PCR a nd digested with appropriate restriction enzymes. The digested fragment was subc loned into the vector obtatined by digestion of plasmid pET-28a(+) with NcoⅠ an d EcoRⅠ. E. coli BL21 (DE3) cells were transformed with plasmids of interst and cultured in LB medium containing ampicillin. Expression of the recombinant protein was induced by the addition of isopropylthio-?-D-galactoside (IPTG). T h e cytotoxity of Stx2a’-LHRH to Hep-2 cells was observed under the microscop y. RESULTS: Recombitant plasmid pET-SL was constructed successfu lly and the clones expressing pET-SL stablely were obtained. A special electroph oretic band in SDS-PAGE (a glycoprotein of 28kD) was noted. Stx2a’-LHRH killed He lp-2 cells clearly. CONCLUSION: In this study, construction of c himeric toxin Stx2a’-LHRH and its expression were described. Moreover, it has o bvious cytotoxity to Hep-2 cell. These finding could open up new vistas in the s tudy of targeted durgs.

A novel genomic island (GI) in Streptococcus suis serotype 2(SS2) was identified, which resided in the highly virulent strains but not in the hypo-virulent strains or avirulent strains of SS2 of the Chinese isolates. This newly discovered GI strain was designated as SSGI4 and its whole length of genome was 11 269 bps, sharing the typical properties of pathogenicity islands, such as the distinct G+C content, a mosaic architecture characteristics and the specificity for virulent isolates. There were 11 genes within SSGI4, in which some genes were putative cell surface protein genes and others were amino acid-binding protein genes. Our finding sheds light on the investigation of horizontal gene transfer in SS2 and their influence on pathogenicity.