Thesis (M.Sc.)--Chulalongkorn University, 2012

The four virulence genes (pvpA, gapA, mgc2 and LP (MGA_0319)) were analyzed from 19 isolates of Mycoplasma gallisepticum (MG) from central, eastern and western parts of Thailand and 2 reference strains including F (vaccine strain) and S6 (ATCC® 15302TM) by PCR (exp. 1). Results revealed the variation in gapA and pvpA genes existence. The gapA and pvpA genes were found in 15 and 4 of 19 isolates, respectively. Whereas, mgc2 and LP genes were detected in all isolates. PCR results of 2 reference strains were positive for all 4 genes. Interestingly, all 4 gapA-negative isolates also performed pvpA-negative PCR results. Additionally, 3 isolates were obtained from the eastern and 1 from western parts; on the other hand, all MG isolates from the central part showed gapA-positive results. The pathogenicity study of 3 Thai MG isolates (58/46, 31/46 and 54/46) and 2 reference strains compared with the control group were determined in chickens (exp. 2) and chicken embryonated eggs (CEE) (exp. 3). The results showed that the pathogenicity study in chickens and CEE were similar. The 58/46 isolate (from the central part, gapA and pvpA-positive) caused the most severe clinical signs, lesion scores and mortality compared with 31/46 and 54/46 (from eastern part, gapA-positive, pvpA-negative) and reference strains did. This experiment suggested that pvpA-negative isolates produced the lower virulent than pvpA-positive isolates.