Identification of antimicrobial resistance-associated genes through whole genome sequencing of high and low MIC isolates of Mycoplasma bovis

Antimicrobial resistance (AMR) in Mycoplasma bovis has previously been associated with mutations within topoisomerases and ribosomal genes rather than specific resistance-conferring genes. This study used whole genome sequencing (WGS) to identify potential new AMR mechanisms. It was found that a 2019 clinical isolate with high MIC (2019-043682) had a new core genome multilocus sequencing (cgMLST) type (ST10-like) and 91% homology with the published genome of M. bovis PG45. Closely related to PG45, a 1982 isolate (1982-M6152) shared the same cgMLST type (ST17), 97.2% homology and similar low MIC results. Known and potential AMR-associated genetic events were identified through comparison with the published M. bovis PG45 genome. Isolate 2019-043682 had 507 genes with non-synonymous mutations (NSMs) and 67 genes disrupted. Isolate 1982-M6152 had 81 NSMs and 20 disruptions. Based on functional roles and known mechanisms of antimicrobials, a 55 gene subset was assessed for potential AMR mechanisms. Of these, 14 were previously identified from other bacteria as sites of AMR mutation, 41 shared similar functions to them, and 11 contained gene-disrupting mutations. This study indicated that M. bovis may obtain high AMR characteristics by mutating or disrupting other functional genes, in addition to topoisomerases and ribosomal genes.