Preparation Of Monoclonal Antibody Against Riemerella Anatipestifer And The Study Of Bacterial Biofilm And OmpA Gene Deletion

Riemerella anatipestifer infection is a contagious disease of ducks, gose, turkeys and various other birds, and has caused the highest mortality among duck diseases. 21 serotypes had been identified by slide and tube agglutination tests with antisera. There was no cross-protection among the 21 serotypes. RA infection has been a continued problem in many duck farms.The precise mechanisms of RA persistence in duck farms are still unknown.In this study, we prepared 14 or 12 monoclonal antibodies (mAbs) against serotype 1 or 2 Riemerella anatipestifer (RA). All 14 mAbs from serotype 1 reacted with all RA strains of serotype 1, 6, 12 and 15 using ELISA. It was suggested that common antigens existed among strains of those serotypes. Importantly, 3 mAbs from serotype 2 reacted with all the strains of different serotypes tested, suggesting common epitope existed among different serotype strains.It was reported that bacterial biofilm was related to the bacterial virulence. In this study, we investigated the ability of 43 RA strains to produce biofilm, tested the effect of various chemical treatments on biofilmed versus planktonic isolates, and challenged ducklings with RA isolates to elucidate whether the ability to form biofilm plays a role in the persistence of RA infections. The result indicated that RA isolates produced biofilm (18 out of 43). Glucose, but not sucrose, was shown to inhibit biofilm formation, antimicrobial agents and detergent often fail to reach bacteria which are enclosed in a biofilm. Although we failed to demonstrate a directly correlation between biofilm-forming ability and virulence in RA, but successfully concluded that biofilmed RA isolates are more resistant than planktonic ones. This conclusion may explain the persistence of RA infections on duck farms, as infections by biofilmed bacteria are difficult to clear and viable biofilm-enclosed bacteria can cause a second infection when conditions are favorable.Using suicide vector, we obtained OmpA deleted mutant from RA strain Th4. The mutant will be helpful for the further study of OmpA as a virulence factor.