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

Multiple genetically distinct M. bovis strains can co-circulate within a single BRD outbreak, complicating control strategies.

This study investigated the genetic diversity of Mycoplasma bovis isolates associated with bovine respiratory disease (BRD) outbreaks in Spanish and Portuguese feedlots. A total of 147 M. bovis isolates collected from 147 BRD outbreaks across 127 feedlots in 30 provinces were characterized using multilocus sequence typing (MLST). Among 141 typeable isolates, 36 distinct sequence types (STs) were identified, with ST8 (21.3%) and ST29 (18.4%) being the most prevalent and geographically widespread. The high Simpson's diversity index (0.892) underscores the substantial genetic heterogeneity of circulating strains. Notably, different STs were found in successive outbreaks within the same feedlot, suggesting ongoing reintroduction or persistence of diverse strains. Whole genome sequencing (WGS) was applied to 19 isolates from five outbreaks with multiple animal samples. Results revealed that isolates differing by more than 700 SNPs could co-exist within a single outbreak, confirming that multiple distinct M. bovis strains can simultaneously contribute to a single BRD event. Conversely, closely related isolates (0–10 SNPs) recovered from different animals within a single outbreak provide strong evidence of clonal transmission. These findings highlight the epidemiological complexity of M. bovis in feedlot settings, with implications for outbreak management, biosecurity protocols, and vaccine development. The combination of MLST and WGS proved valuable for characterizing both inter- and intra-outbreak diversity, offering a robust framework for future epidemiological surveillance of M. bovis.

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