Molecular epidemiological studies are of great significance to reveal the population structure, genetic diversity, and prevalence of Mycoplasma spp [4, 15], which facilitates the formulation of effective prevention and control measures, including the development of vaccines and diagnostic methods[4, 16]. MLST studies performed on 44 strains from nine Chinese provinces from 2008 to 2014 showed that ST10, ST32, and ST43 were found in Hubei province (n=25) and that ST10 was also found in Anhui (n=1), Fujian (n=2), Hunan (n=1), Henan (n=8), Inner Mongolia (n=1), Jiangxi (n=3), Guangzhou (n=2), and Shandong (n=1) province . However, there are no reports about the MLST study of M. bovis in Ningxia Hui Autonomous Region. Therefore, this study is the first report on the molecular epidemiology of M. bovis from 2009 to 2018 in Ningxia Hui Autonomous Region.
At present, there are seven STs in M. bovis in China including ST10, ST26, ST32, ST43, ST134, ST172, and ST173. ST10 is widely prevalent in all provinces reported in China, including Ningxia Hui Autonomous Region (n=37, 56.9%) where are no MLST reports. After the ST10 strain was first isolated in 2010 in Ningxia Hui Autonomous Region, the ST10 of M. bovis could be isolated and identified every year. And it has been widely diffused in different cities in Ningxia Hui Autonomous Region. Interestingly, the ST10 strains have been reported that were widely distributed in American, Australia, and Israel. Previously, the international spread of contagious bovine pleuropneumonia was shown to be linked to the movement of cattle[4, 17, 18]. So, it is a similar transfer probably that through international movement of cattle and domestic movement of cattle caused the widespread distribution of the M. bovis ST10 in China and even in Ningxia Hui Autonomous Region. The reason for the widespread prevalence of ST10 strain in Ningxia Hui Autonomous Region may be that the Ningxia Hui Autonomous Region government strongly supports the construction of large-scale cattle breeding parks. For their expansion, intensive cattle farms had to purchase cattle from different provinces of China and different countries in the world, but M. bovis was ignored, which led to the widespread presence of exogenous M. bovis in Ningxia Hui Autonomous Region. It is speculated that the prevalence of M. bovis ST10 in Ningxia Hui Autonomous Region began in 2010.
In 2009, our lab isolated M. bovis from the lung tissue of cows for the first time, which was ST134. From 2009 to 2018, ST134 (n = 28, 43.1%) was isolated and identified from different cities of Ningxia Hui Autonomous Region. However, it has not been identified in other provinces in China. Therefore, it confirmed that ST134 strains were closely related strains with the same origin in Ningxia Hui Autonomous Region, China, and has been widely distributed in Ningxia Hui Autonomous Region for many years.
To evaluate the evolutionary relationship of M. bovis between isolates from Ningxia Hui Autonomous Region and isolates from other provinces in China, a phylogenetic tree was constructed based on concatenated sequences. The evolutionary analysis showed that all ST10 strains were in the same lineage as ST26, ST32, ST43, ST172, including Ningxia Hui Autonomous Region ST134 strains. However, the ST173 strains were in the same lineage as the ST17 strain. The study results indicate that the M. bovis strains with STs different from ST173 and ST17 were closely related strains with the same origin.