TDK conference 2019

Mycoplasma hyorhinis is a facultative pathogen bacterium, common member of the microbial community of the upper respiratory tract of swine. Manifestation of clinical signs is triggered by stress, related to inadequate housing conditions and presence of co-infections. Systemic infections usually occur in piglets between 3 to 10 weeks old, with typical symptoms like polyserositis, arthritis and less often otitis and conjunctivitis. In the past few years the detection of M. hyorhinis in piglets showing these symptoms has increased. Protection against the infection is rely upon the better understanding of the pathogen. For the determination of the source of infection it is crucial to develop genotyping methods which are well standardized and comparable between laboratories. Nowadays, the PCR based methods MLST (multi locus sequence typing) and MLVA (multiple-locus variable-number tandem repeat analysis) are the common techniques for genotyping.

MLST system is publicly available for genotyping M. hyorhinis isolates. MLST is capable to detect mid-term evolutional distances and to determine relationships between the strains, based on point mutations in house-keeping genes. We determined the MLST profile of 37 M. hyorhinis isolates from Hungary, and the analyses showed identical sequence types in isolates originating from the same farms.

MLVA discriminates strains based on the repeat number of tandem repeat units in intergenic regions. We developed an MLVA system for genotyping M. hyorhinis based on six regions. These regions usually harbor mutations, because they do not code any genes, therefore can be used for the analysis of short-term evolutional distances. The sensitivity of the developed MLVA system is 103 copy number, and there are no cross-reactions with any other common swine pathogen Mycoplasmas (M. hyopneumoniae, M. hyosynoviae, M. flocculare). The developed method is suitable for diagnostics due to its sensitivity and specificity.

The MLVA analyses of 37 Hungarian M. hyorhinis isolates showed that the strains clustered into two main groups, similarly to the results of the MLST analyses. However, all strains represented unique MLVA profile, differentiating strains isolated from the same farm in different years. Thus the developed MLVA system is suitable for the resolution of the MLST phylogenetic tree, and can be applied as a complementation of the MLST analysis, providing a molecular tool of high discriminatory power for epidemiological investigations.