| Doctor candidate: Gao SongAdvisor:Prof. Liu XiuFanChapter 1: Serogroups and outer membrane protein patterns of avian pathogenic Escherichia coli isolated from some regions in China595 avian Escherichia coli isolates derived from specimens of diseased birds coming from 18 provinces in China were identified by standard biochemical procedures. Among these E.coli isolates, 440 were placed in determined serogroups, 144 were unable to be classified as certain group, and 11 were self-agglutinated. These isolates distributed in 60 serogroups and 60% belonged to 10 0 serogroups: 018, 078, 02, 088, 011, 026, 04, 01, 0127 and 0131. Isolates in these 0 serogroups were 262 in total, out of which 204 belonged to 018, 078, 02, 088, 011 and 026. Therefore they were predominant serogroups.The relative pathogenicity of 60 Escherichia coli isolates in predominant serogroups from different regions was evaluated in specific-pathogen-free (SPF) dayold chickens. Six birds per isolate were inoculated intratracheally with 0.lml of a 24hour Luria-Bertani (LB) broth culture containing i07 colony-forming units (CFU) of E.coli. Based on mortality and lesions examined during a 7-day postinoculation period, 83.33%, 10% and 6.67% of the isolates were characterized as with high, intermediate and low pathogenicity respectively. The pathogenicity of 30 isolates from other common serogroups which belonged to 04, 01, 0127 and 0131 serogroups, and 10 isolates from uncommon serogroups was also evaluated by the same way in susceptible day-old chickens, and 90%, 10% and 0% of these isolates were with high, intermediate7and low pathogenicity respectively. These results suggested that all the Escherichia coli isolates we identified were pathogenic, in which more than 83% were highly pathogenic, less than 17% were intermediately to low pathogenic.The outer membrane protein (OMP) patterns of 204 avian Escherichia coli isolates in predominant serogroups of 018, 078, 02, 088, 011 and 026 originated from 18 provinces, autonomous regions and municipal cities in China were characterized. The outer membrane proteins of these isolates were isolated with the modified Nlauroylsarcosine method and analyzed by SDS-PAGE. Four different OMP patterns were identified with these isolates of predominant serogroups. Three different OMP patterns with 56 isolates of 018, 4 with 54 isolates of 078, 2 with 28 isolates of 02, 1 with 26 isolates of 088, 3 with 22 isolates of 011 and 1 with 18 isolates of 026 respectively, were found. Isolates with OMP pattern 1 were distributed in 6 different serogroups, and OMP-3 pattern was also shared by isolates in 018, 078 and 011 serogroups. These results indicated that the OMIP patterns of avian pathogenic Escherichia coli isolates of 018, 078, 02, 011 serogroups which were isolated from different regions in China were heterogeneous, however, all isolates in serogroups 088 and 026 belonged to OMP pattern 1. Moreover, the OMP pattern 1 was shared by isolates in six different predominant 0 serogroups.Chapter 2: Experiment studies of immune protection mechanism of avian colibacillosisChickens were immunized with vaccine preparations of the 018 and 078 isolates of avian Escherichia coli inactivated by ultrasonic treatment. The results of the challenoæŠ revealed that the 078 isolate vaccine provided the greatest protection against the challenge of 078 isolates with the same or different outer membrane protein pattern (OMP pattern), and the 018 isolate vaccine only provided the best protection against the challenge of 018 isolate with the same OMP pattern but did not offer protection against challenge of 018 isolates with different OMIP patterns. There was no evidence that these vaccines provided any protection against challenge isolates in different8ThJ]1 k j~: t~ ?~IE? ~ZZserogroups no matter whether the vaccine isolate and challenge isolate share the same OMP patterns or not.Antibody responses of chickens to OMPs and lipopolysaccharides (LI扴) antigen...
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