Abstract
Antimicrobial resistance (AMR) in Mycoplasma bovis has been previously associated with topoisomerase and ribosomal gene mutations rather than specific resistance-conferring genes. Using whole genome sequencing (WGS) to identify potential new AMR mechanisms for M. bovis, it was found that a 2019 clinical isolate with high MIC (2019-043682) for fluoroquinolones, macrolides, lincosamides, pleuromutilins and tetracyclines had a new core genome multilocus sequencing (cgMLST) type (ST10-like) and 91% sequence similarity to the published genome of M. bovis PG45. Closely related to PG45, a 1982 isolate (1982-M6152) shared the same cgMLST type (ST17), 97.2% sequence similarity and low MIC results. Known and potential AMR- associated genetic events were identified through multiple sequence alignment of the three genomes. Isolate 2019-043682 had 507 genes with non-synonymous mutations (NSMs) and 67 genes disrupted. Isolate 1982-M6152 had 81 NSMs and 20 disruptions. Using functional roles and known mechanisms of antimicrobials, a 55 gene subset was assessed for AMR potential. Seventeen were previously identified from other bacteria as sites of AMR mutation, 38 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.
Highlights
Mycoplasma bovis is a member of the Mollicutes; membrane-bound bacteria which lack a cell wall, precluding the use of many common antimicrobial agents such as the β-lactams [1]
Cultures of two isolates of M. bovis (1982-M6152 and 2019-043682) and M. bovis strain PG45 were tested in triplicate for minimum inhibitory concentration of 16 antimicrobials (Table 1), with the results of MIC testing identical within each triplicate
Of the M. bovis genes previously linked by Sulyok et al with Antimicrobial resistance (AMR) for various classes of antimicrobial, two sites linked with fluoroquinolone resistance display multiple non-synonymous mutations (NSMs) for the high-MIC isolate 2019-043682 and no NSMs for the low-MIC
Summary
Mycoplasma bovis is a member of the Mollicutes; membrane-bound bacteria which lack a cell wall, precluding the use of many common antimicrobial agents such as the β-lactams [1]. M. bovis is a causative agent of pneumonia, arthritis, otitis media, and reproductive disease and is a contributor to the bovine respiratory disease (BRD) complex, known as ‘shipping fever’, which is a major source of morbidity, mortality and financial loss in calf and feedlot operations. M. bovis is capable of persisting for the life of a colonized animal, which may remain asymptomatic while acting as a source of infection for herdmates or offspring [1,2]. Given the asymptomatic nature of many M. bovis infections, and the high rates of colonization when animals are co-mingled (potentially over 90%) [4,5], conditions are favourable for the development of multi-drug resistant strains. With global rates of antimicrobial resistance increasing, understanding the molecular mechanisms underlying antimicrobial resistance, for multi-drug resistant
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