Isolation And Identification As Well As S1 Gene And M Gene Sequence Analysis Of Avian Infectious Bronchitis Virus XT Strain

In this study, a strain of avian infectious bronchitis named XT was isolated from pathological materials of suspected illness chickens which come from a farm in Xing Tai area, He Bei province. The p Hysicochemical and biological characteristics were identified and the hereditary variability was analyzed by sequencing and comparing the gene.The trachea, kidney and glandular stomach sterilely collected from suspected IB chickens were grinded into virus liquid which would passage in chicken embryos and be collected. Allantoic fluid treated with 1% pancreatin could agglutinate erythrocyte, but couldn’t do it without 1% pancreatin. NDV replication has been interfered by XT virus so as to the titers have decreased by 2 to 3 in NDV interference test. Compared with control group, the development of test group was extremely slow after inoculating XT allantoic fluid by SPSS V17 analyzing which shows that XT strain can dwarf chicken embryo. In animal regressive research, typical clinical and anatomic symptoms were appearing after inoculating XT allantoic fluid, pathological materials were collected and been tested by IBV RT-PCR diagnosis kit, the result shows that all animal of control group are negative and most of the test group are positive which indicate chickens have infected IBV in varying degree.PHysicochemical characteristic tests show that XT strain is resistant to acid(p H 3.0) and base(p H 11.0)but more resistant to acid, can be decreased virus titer by heat however can be improved when add Mg2+, is sensitive both to ether and chloroform with which treated the titer has decreased by 2 to 3, all the characters above are confirming to IBV. According to determination, the EID50 of XT strain is 10-5.69/0.1ml. Serological cross-neutralization test displays that the relationship coefficient R between XT strain and immune strain H120, W93 are respectively 77.98%, 44.88% which indicate they are different sub-serotypes of the same serotype on the basis of determination standard(when R>80%, the two strains are the same serotype; when 25%<R<80%, the two strains are different subserotypes of the same serotype; when R<25%, the two strains belongs to different serotypes).In this study, S1 gene and M gene sequence of XT strain were cloned and sequenced, further analyzed comparing with 18 reference strain published in Genbank, the result shows that the homology between XT S1 gene and domestic common vaccine strain H120, H52, Ma5, M41, W93 are in low level ranging from 76% to 77%, however, it’s relatively high when compared with isolate strain WF from Shan Dong, the nucleotide homology is 91.3%, the amino acid homology is 90.9%. The case of M gene homology between XT and 18 reference strains is basically consistent with S1 gene, but is higher than it overall, which indicate that M gene is more conserved than S1 gene. Sequence comparison reveals that the homology between XT strain and domestic common vaccine strains is low, and WF is high.