Variability of pMGA/vlhA sequences among Mycoplasma gallisepticum field strains isolated from laying hens and their deformed eggs

Abstract

Mycoplasmosis, attributed to Mycoplasma gallisepticum, poses a significant challenge to poultry farming, leading to substantial economic losses and persistent infections within flocks. This bacterium harbours various surface proteins that are crucial for adhesion, transporter activity and evasion of the host immune response, facilitating its pathogenicity. One such key surface lipoprotein, referred to as pMGA or vlhA haemagglutinin, plays a pivotal role in adhesion processes. In this study, the clonal regions pMGA1.2 and pMGA1.3, as reported by Markham (M83178.1), were investigated to elucidate differences or similarities in the whole DNA sequences of M. gallisepticum field strains. The aim was to analyse sequence diversity within this region. Six internal primers were designed to amplify the target sequence, and isolates were obtained from both eggs and chickens sourced from laying hen flocks. Identification revealed 17 strains of M. gallisepticum and four strains of Mycoplasma synoviae, which were confirmed through the mgc2 and 16S rRNA genes, respectively. Positive and negative controls were established using the MGS6 and MSWUV1853 strains. Amplification results indicated a higher frequency of amplification proximal to the C-terminal region, with segments 4 (33.3 %) and 6 (27.8 %) being the most prevalent. Notably, none of the field strains exhibited the same amplification pattern as MGS6, and none of the strains characterized as M. synoviae amplified any primer set. Upon translation, the amino acid sequences from segments 4 and 6 were found to be compatible with conserved sequences within the Myco_haema protein domains of the genus Mycoplasma, specifically corresponding to Q7NAP3_MYCGA VlhA.3.04. The observed homology suggests a potential genetic transfer, while the variability identified in the pMGA or vlhA gene region of the field strains may have significant implications for protection against M. gallisepticum infection in chickens.