Mycoplasma gallisepticum (MG) is an economically important pathogen of poultry worldwide. Genetic characteristics, Infectivity, tissue tropism and pathogenicity differ significantly between MG strains. The aim of this study was to analyze the partial DNA sequence of mgc2, a cytadhesin-encoding gene of MG isolates from broiler breeder flocks in Tehran province, Iran and compare them with MG isolates from other countries. For this purpose, a total of 320 samples were collected from choanal cleft and trachea of broiler breeder flocks with positive RSAT. 38 out of the 320 samples were positive in culture and reacted with specific antisera. The 15 positive samples were subsequently selected for molecular study. The PCR products containing mgc2-cytadhesine gene were generated with specific primers and then sequenced. Alignment and comparison of the sequences in DNASIS program revealed that 3 isolates were quite similar and 12 other isolates were different from first group. Based on clustal-W alignment and phylogenetic analysis of 15 MG feild isolates and 25 MG isolates and strains from other countries (available in GenBank ), the feild isolates were arranged in two distinct groups with 97/6-98/3 percent homogeneity and each one of two groups had higher homogeneity (Up to 99/6 percent) with some of the isolates and strains of MG from other countries. Our study revealed heterogeneity between MG isolates from broiler breeder flocks in Tehran province, Iran and high mgc2 gene- homology between MG isolates of Tehran province origin and some of the MG strains and isolates from other countries. This results can represent the precence of different MG isolates due to the existence of multiple sources of pollution and epidemiological relationships or MG mutagenesis for adaptation to environmental conditions.
