Objectives: Avibacterium paragallinarum (AP) is a causative agent of infectious coryza, a contagious bacterial respiratory disease of chickens with substantial economic losses. AP was isolated from an Infectious coryza outbreak in a layer flock in Mashhad, Iran. As there was no report for circulating AP serotypes in Iran, therefore, this study was conducted to determine the serotype and further information of the isolate by Multiplex PCR and nucleotide sequence Analysis of Hypervariable Region of Its HMTp210 gene. Material &Method: Isolation of the AP was carried out on blood agar culture cross-streaked with a NAD positive Staphylococcus. Bacterial DNA extraction was made by boiling method. A specific PCR assay was performed to confirm identity of the isolate. Then a Multiplex PCR targeting hypervariable region of HMTp210 gene was employed to detect the A, B and C serotypes. Furthermore, the entire length of hypervariable region of this gene was also amplified, sequenced followed by multiple alignment and phylogenetic analysis. Result &Conclusion: On blood agar, the isolate showed tiny dewdrop and nonhemolytic colonies with satellitic growth pattern. The PCR using specific primers for AP confirmed the identity of the bacteria. Moreover, the Multiplex PCR revealed that the isolate could be belong to serovar A. Nucleotide sequence analysis of the region, except for three nucleotide substitutions at positions 75‚443 and 1010, were identical to available sequence data of AP, serovar A. Due to lack of sequence data of other AP serovars in this region, we consider that sequence data of the this regionand its phylogenetic tree might be employed as an initial approach, but not as an unique molecular marker, for serovar differentiation of AP isolates.

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