Sequence analysis of the S1 gene of the vaccinal strains (H120&H52) of infectious bronchitis virus during serial passages in embryonated eggs.
2012
Mehran Bakhshesh
Infectious bronchitis (IB) caused by a gamma-coronavirus is one of the most acute and contagious diseases affecting mainly respiratory tract of chickens with worldwide distribution. The existence of a very large number of IBV- serotypes and variants which insufficiently induce cross protection against each other is the major problem to control the disease. Among viral proteins, the subunit protein S1 (Spike) plays the principle role in inducing neutralizing antibodies which defines serotypes and attachment to the host cells. A few amino acid differences in the S1 result in the change of strains and serotypes. Therefore, analysis of sequences of S1 is very important to characterize field isolates and to define their degree of identity with vaccine strains. To characterize H52 and H120 strains and their serial embryonated egg - passaged of Razi institute, this study was performed. The results revealed that H52 and H120 strains of Razi institute are identical to the standard of strains in the Gene Bank. In addition, H120 strains was completely stable after 5 passage in embryonated egg, however, H52 strain showed one amino acid change from passage 3 at position 118 from Glycine (G) to Valin (V) which remained stable to 5th passage . Interestingly, passage 3-5 of H52 strain is 100% identical to H120 strain. Comparison of the both diverse H52 passages determined that they are both identical to H52 and H120 strains registered in Gene Bank meaning that this minor change could not affect the function of egg-passaged H52 strain. To better characterization of these strains and their serial embryonated egg - passaged, analysis of other genes involved in virulence and pathogenesis of the virus and performing protective tests against field strains are recommended.
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