Genetic variability of Mycoplasma hyorhinis in German and Swiss pig farms

Mycoplasma hyorhinis is a common inhabitant of the upper respiratory tract and tonsils of pigs. Its role as a potential respiratory pathogen remains controversial. Information on the population structure of M. hyorhinis might help to get a clearer picture on specific strains in the pig population involved in clinical disorders. Using multilocus sequence typing (MLST) we therefore genetically characterized M. hyorhinis isolates from Swiss and German pig herds previously included in a transnational cross-sectional study determining the prevalence of M. hyorhinis.

A fresh culture of 60 M. hyorhinis isolates from stocks kept at -80°C was prepared and an aliquot was lysed at 96° C for 15 minutes and then submitted to PCR. All primers for the six target genes used in the MLST scheme of Tocqueville et al. (J.Clin.Microbiol. 2014) were newly designed to allow amplification and sequencing with a single protocol. The resulting sequences of the target genes adk, dnaA, gltX, gmk, gyrB, and rpoB contained the corresponding sequence parts used for allele definition on the PubMLST database (pubmlst.org). Edited sequences were entered to Bionumerics® and sequence types (ST) defined using the MLST plugin. New alleles and allele combinations were submitted to the PubMLST database.

A total of 25 ST were observed with the 60 strains, 24 of them were new types. Only one ST was previously observed with a French isolate. Generally, identical genotypes were observed within most farms. The same genotype was also observed in three different Swiss farms. On the other side different genotypes were found within 3 German farms and even within single animals from German farms.

The study revealed that MLST based on the six housekeeping genes is a very useful tool to analyze M. hyorhinis genetic variation and population structure. Data obtained shows a high variability of the Mycoplasma hyorhinis strains with, however, some limited clonality. The high diversity of both Swiss and German strains indicates that recombination of the M. hyorhinis genome is common and similar to what is observed for M. hyopneumoniae. Similar to this pathogen the population structure of M. hyorhinis also shows some limited clonality with predominant genotypes within a single herd and different ones between herds. This is more pronounced with Swiss strains where genotypes seem somewhat more conserved than strains in German farms. The similar population structure of M. hyopneumoniae and M. hyorhinis could indicate a kind of co-selection of the two species.

Disclosure of Interest: None Declared.