Genetic diversity of Mycoplasma bovis associated with bovine respiratory disease outbreaks.

Mycoplasma bovis is one of the main bacterial pathogens involved in bovine respiratory disease (BRD) outbreaks and is commonly found in feedlots worldwide. This study investigated the genetic diversity of M. bovis within and between BRD outbreaks occurring in Spanish feedlots and compared it with results obtained elsewhere. A total of 147 M. bovis isolates from 147 BRD outbreaks in beef fattening cattle from 127 feedlots located in 30 different provinces of Spain ( n= 123 feedlots) and Portugal ( n= 4 feedlots) were characterized by multilocus sequence typing (MLST). A total of 36 different STs were detected among the 141 typeable M. bovis isolates analyzed (Simpson’s diversity index =0.892). ST8 (21.3%) and ST29 (18.4%) were the most frequent and widely distributed geographically STs, with no other accounting for >10% of the isolates. Different STs were identified in successive outbreaks occurring in the same feedlot. In addition, 19 isolates from five BRD outbreaks in which more than two isolates from different animals were available were subjected to whole genome sequencing (WGS) to assess M. bovis intra-outbreak genetic diversity: isolates belonging to different STs separated by > 700 SNPs were found within a single BRD outbreak, indicating that more than one strain of M. bovis can be involved simultaneously. Nevertheless, the presence of closely related isolates (0-10 SNPs) in different animals from a single outbreak strongly suggests clonal spread. Our results demonstrated the high genetic diversity of M. bovis circulating in Spanish feedlots and the dynamism and complexity of the M. bovis epidemiology.