Mycoplasma bovis in Nordic European Countries: Emergence and Dominance of a New Clone

Abstract

Mycoplasma (M.) bovis is an important pathogen of cattle implicated in a broad range of clinical manifestations that adversely impacts livestock production worldwide. In the absence of a safe, effective commercial vaccine in Europe, the reported reduced susceptibility to antimicrobials for this organism has contributed to difficulties in controlling infection. Despite global presence, some countries have only recently experienced outbreaks of this pathogen. In the present study, M. bovis isolates collected in Denmark between 1981 and 2016 were characterized to determine (i) genetic diversity and phylogenetic relationships using whole genome sequencing and various sequence-based typing methods and (ii) patterns of antimicrobial resistance compared to other European isolates. The M. bovis population in Denmark was found to be highly homogeneous genomically and with respect to the antimicrobial resistance profile. Previously dominated by an old genotype shared by many other countries (ST17 in the PubMLST legacy scheme), a new predominant type represented by ST94-adh1 has emerged. The same clone is also found in Sweden and Finland, where M. bovis introduction is more recent. Although retrieved from the Netherlands, it appears absent from France, two countries with a long history of M. bovis infection where the M. bovis population is more diverse.

Keywords: Mycoplasma bovis; antimicrobial resistance; cattle; genomic epidemiology; phylogenetics.

Figure 1

Nucleotide identity matrix for all isolates. Color values denote high (red) and lower (blue) similarity for each pairwise comparison. Clusters are based on complete linkages.

Figure 2

Phylogenetic tree based on cgMLST as generated by FastTree and stratified by body site of isolation and country and labeled by year of isolation. The PG45 type strain from the USA as well as two Chinese isolates (Chinese cluster) and the recent Swiss isolate, JF4278, were included for comparison. The Chinese Hubei-1 isolate was used as an outgroup. The core genome was generated by Roary and was constituted of 500 genes out of a total of 1807 genes. nk, not known.

Figure 3

Minimum spanning tree, based on the MLST-1a from Register et al., 2015. Strains from this study are color-coded. The two isolates from China included for comparison are in grey.

Figure 4

Comparison of MIC distributions of five antimicrobials for 81 Mycoplasma bovis isolates collected in Denmark and five other Northern and Western European countries between 1981 and 2017. X-axis, MICs in µg/mL; Y-axis, number of isolates. Black blocks represent old Danish isolates collected prior to and including 2000, striped blocks are for more recent Danish, Swedish, and Finnish isolates, with white blocks for recent isolates from Estonia, France, and the Netherlands. Arrows indicate break points for clinical categorization according to the CLSI standards for Pasteurellaceae. Any MICs above the plain arrow will categorize the strain as “Resistant”, any MICs above the dotted arrow will categorize the strain as “Intermediate or Resistant”.