Genotyping Mycoplasma gallisepticum by multilocus sequence typing.

Mycoplasma gallisepticum causes chronic respiratory disease and reproductive disorders in many bird species, resulting in considerable economic losses to the poultry industry. Maintenance of M. gallisepticum-free flocks is the most adequate method to control infection. To this end, monitoring systems and vaccination programs with live vaccine strains are applied worldwide. There is strong demand for efficient epidemiological investigation tools to distinguish M. gallisepticum strains in order to control disease. Up to now, multilocus sequence typing (MLST) has been regarded as gold standard for genotyping bacteria due to its good reproducibility and high discriminatory power. The aim of this study was to develop an MLST assay which can determine phylogenetic distances between M. gallisepticum strains. After analysing more than 30 housekeeping genes, six loci (atpG, dnaA, fusA, rpoB, ruvB, uvrA) were selected for the MLST assay due to their genomic location and high diversity. Examination of 130 M. gallisepticum strains with this MLST method yielded 57 unique sequence types (STs) with a 0.96 Simpson's index of diversity. Considering the large number of STs and high diversity index, this MLST method was found to be appropriate to discriminate M. gallisepticum strains. In addition, the developed method was shown to be suitable for epidemiological investigations, as it confirmed linkage between related strains from outbreaks in different farms. Besides, MLST also suggested high impact of extensive international trade on the spread of different M. gallisepticum strains. Furthermore this method can be used for differentiation among vaccine and field strains.