| Summary: | 碩士 === 國立中興大學 === 微生物暨公共衛生學研究所 === 105 === Avibacterium paragallinarum is the causative agent of infectious coryza (IC), an important acute respiratory disease that leads to growth retardation and reduced egg production of chickens . The hemagglutinin (HA) protein plays a key role in virulence and immunogenicity of Av. paragallinarum, and HA has been sub-typed into three serotypes: A, B, and C. Field strains of Av. paragallinarum isolated previously in Taiwan are known to be serotype C. In this study, we used hemagglutination inhibition (HI) tests to identify the serotype of two strains of Av. paragallinarum (TW15-B1 and TW16-3) isolated in Taiwan in 2015-2016. The results showed that the antisera against reference strains 221 (serotype A), H18 (serotype C) and TW07 (Taiwanese strain of serotype C) failed to react with strains TW15-B1 and TW16-3, indicating that TW15-B1 and TW16-3 are not conventional serotype A or C strains. Although the antisera prepared TW15-B1 and TW16-3 did not react with strain 221 or H18, these two sera reacted with strain TW07, suggesting that TW15-B1 and TW16-3 are serotype-C-like strains. Sequence comparisons showed that the HA protein sequence of TW15-B1 is highly similar to that of TW16-3, but differs from those of strains 221, H18 and TW07. Moreover, the most diversified sequences are located at the N-terminal portion of the HA protein. These finding suggested that sequences at the N-terminal portion of HA might play an important role in determining the serotypes of TW15-B1 and TW16-3. Taken together, these results showed that TW15-B1 and TW16-3 have a serotype that cannot be determined by HI test using the antisera prepared from the conventional references strains 221 and H18. This result is important for identification of serotype and selection of vaccine strains against Av. paragallinarum in Taiwan.
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