The Pathogenic Mechanism Of YenI Gene In Avian Pathogenic E.Coli (APEC)

Avian colibacillosis is one of the most serious diseases in poultry industry, caused partly or entirely by Avain Pathogenic E.coli (APEC). Acute or chronic infection result in respiratory tract infection or septicemia, which caused huge economic loss all over the world. With the development of intensified raising farm methods, APEC infection cases have been reported in most provinces and areas from China. The mechanism of pathogenesis and prevention and control were always been studied hard, however clarified answer towards APEC infection have not been well solved. Virulence factors are strictly regulated by Quorum Sensing system, and in this study, regulation function of Quorum Sensing-I upon APEC strain have been explored.During growth period, bacteria can utilize Quorum Sensing system to sense cell population density in surrounding environment, therefore to regulate gene expression. This regulation mechanism is called Quorum Sensing, while the signaling molecules in QS are known as auto-inducer. In QS-I, E. coli encodes a single LuxR homolog named SdiA, but does not express the LuxⅠ homolog, the acyl-homoserine lactone (AHL) synthase, which produces AI-1. APEC can regulate its virulence gene expression in response to exogenous AHLs, but QS-Ⅰ regulatory mechanism in APEC are still unknown.This study targets APEC CE129 isolate as the reference strain, and Yersinia enterocolitica yenⅠ genewas cloned and transformed into APEC CE129. The pSB01 biosensors was used to detect the C6-AHL production ability of CE129. CE129 SdiA mutant strain with in-frame sdiA gene deletion was constructed by λRed recombination system, which lost the ability to sense AHL. Growth curve shows CE129, CE129/pyenⅠ, CE129△sdiA and CE129/pBR have no significant difference in growth in vitro. The results of competition test in vitro show that CE129/pyenⅠ have no competition advantage over the mutant CE129△sdiA. Bioflim was examined on surface of the glass, polystyrene and gas liquid interface in glass tubes under AHL influence, which reduced obviously.In serum bactericidal test and antibiotic resistance test, CE129/pyenⅠ has the same results as the CE129 did. The results of swimming test and flagella gene fliC of fluorescence quota PCR examination show that C6-HSL has no effect on the flagella gene fliC, which is different from EHEC and ETEC; CE129/pyenⅠ anti-acid gene gadA expression quantity was lower by 37.1%; in the anti-acid test, CE129//pyenⅠ and CE129 have the same acid resistance. These results may also from genetic background differences of APEC strains. HD11 cell phagocytosis test and DF1 cell adhesion test results show that the anti-phagocytosis and the adhesion ability of CE129/pyenⅠ is better than CE129. However, expression level of type Ⅰ fimbria decreased, in addition to unchanged level of flagella. Expression changes of lsrR pointed complicated regulation exist in QS-1 and QS-Ⅱ system, which has been illustrated in our early study. To sum up, QS-1 regulates APEC virulence in some aspects, but biofilm, flagella and acid tolerance may derive from genetic background or different infection routes, which need our further study.