A core genome multilocus sequence typing scheme for Mycoplasma hyorhinis

Mycoplasma (M.) hyorhinis is a commensal and pathobiont residing in the upper respiratory tract in swine and with the ability to spread systemically, mainly causing polyserositis and polyarthritis in nursery pigs. Since little is known on the epidemiology of M. hyorhinis infection, whole genome sequences of 73 strains isolated from pigs in Austria (n = 71) and Germany (n = 2), that have been isolated from clinically affected pigs during routine diagnostics, and publicly available genomes of eight M. hyorhinis strains were analyzed in the presented study. For this purpose, a core genome multi locus sequence typing (cgMLST) scheme encompassing 453 target genes was developed using the Ridom© SeqSphere + software. Results were compared to two previously described conventional MLST schemes and to a core genome single nucleotide polymorphism (cgSNP) analysis approach. Core genome MLST showed high diversity among the M. hyorhinis strains studied and while certain isolates from one farm or a single animal formed cgMLST clusters (≤ 8 allele differences), no isolates with identical allele profiles were identified. In addition, cgMLST had superior discriminatory power (Simpson's ID = 0.995) over conventional MLST (Simpson's ID = 0.952 and 0.985), while demonstrating a lack of congruence between conventional MLST and genome-wide relationship. Core genome SNP results were highly congruent with cgMLST results but lacked in resolution when comparing closely related isolates. Thus, cgMLST is the most suitable method for epidemiological investigations such as outbreak analysis, and to gain insights into M. hyorhinis population structure.