MOLECULAR CHARACTERIZATION AND STRAIN DIFFERENTIATION OF THAI MYCOPLASMA SYNOVIAE ISOLATES BY SEQUENCING OF PARTIAL VLHA GENE

Abstract

Mycoplasma synoviae (MS), a remarkable pathogen in poultry industry, causes subclinical infection of upper respiratory tract and an infectious synovitis especially in the tendon sheaths and synovial membranes of joints. In addition, vaccination at farm level might have limitation because the information on diagnostic tests to differentiate field and vaccine strains was deficient. Although the specific detection of MS, 16S rRNA gene-based PCR, has been widely used to detect MS infected flocks, the sequencing of these gene is not suitable for strain differentiation. The vlhA gene-based PCR was designed to differentiate MS strains because it is encoding for hemagglutinin protein and other immunodominant membrane proteins which can be involving in colonization, antigenic variations, and virulence. The sequence analysis of vlhA gene were useful for typing and subtyping of MS strains based on the nucleotide insertion/deletion of proline-rich repeat (PRR) region and the nucleotide polymorphisms of RIII region in vlhA gene fragments. This study was designed to characterize Thai MS field isolates and to determine the strain differentiation between Thai field strains and vaccine strain by using sequence analysis of partial vlhA gene. In total, 20 MS field isolates submitted from registered chicken farms in Thailand during 2015, were identified as C1 (n=1), C2 (n=4), E1 (n=9), E2 (n=1), and L (n=5). The results revealed that six of nine isolates resulting in respiratory signs were type E1. In addition, four isolates from lame chickens showing joint swelling were type L with 105 nucleotides length. This study provides the first molecular data of Thai MS isolates and the first evidence of type L for being arthropathic strain. Furthermore, co-infection of MS types E and L was observed in one farm while other farms were affected by only one type of MS. The result indicated that sequence analysis of partial vlhA gene can be used as a tool for tracing MS characterization.