Mycoplasma hyopneumoniae variability highlights the need for new terminology

In this latest article published in Transboundary and Emerging Diseases, Dr. Alyssa Betlach, phD candidate in Dr. Maria Pieters lab, reviews the observed variability in Mycoplasma hyopneumoniae, the effect it can have in swine farms and how a better terminology is possible to improve scientific communication.

Mycoplasma hyopneumoniae variability

A limited variation in M. hyopneumoniae antigenic profiles

Few Mycoplasma proteins have antigenic properties. P36, P43, P44, P50, P65, P70, P74, P76, and P97 among others have been identified as creating an immune response. Variations in the antigenic profile between strains has been described by various researchers. The proposed explanations for such changes are modifications of the size or expression of proteins as well as an evolution of Mycoplasma hyopneumoniae to adapt to its environment.

However, the antigenic variations are limited within and between species. Since numerous proteins cross-react between Mycoplasma hyopneumoniae and other swine mycoplasms such as Mycoplasma hyosynoviae or Mycoplasma hyorhinis. These findings suggest that the antigens are intrinsically related to the survival and the pathogenesis of the organism.

High variability found in M. hyopneumoniae proteins

Mycoplasms like other bacteria, show a decrease in the expression of genes coding for metabolism-related proteins in adverse conditions. Additionally, a high variability in total proteins has been noted between strains. This finding was not influenced by the geographical source of the isolate. It has also been reported that proteins highly varied between strains of different virulence but that the two are not necessarily related.

Post-translational modifications occur frequently in Mycoplasma hyopneumoniae functional proteins because there is little regulation of the transcription process. These changes have been shown in cell surface proteins which means that they could regulate the outside topography of Mycoplasma and influence parameters such as cell adhesion.

Pathogenicity and virulence

Little is known regarding the mechanisms underlying Mycoplasma hyopneumoniae virulence. P97 may be required for cilium binding whereas Locus 1 protein could be associated with increased virulence. Moreover, it is unclear is being infected by several strains at the same time increases the severity of lung lesions in the affected pig.
Mycoplasms are intrinsically resistant to numerous antibiotic classes and acquired resistances against some macrolides, fluoroquinolones, tetracyclines, and lincosamides have also been shown.

Genomic variability

Numerous evidence has been shown of genomic variability across Mycoplasma strains. Genomic variability seems to increase with the geographical distance the strains originated from. Indeed, two strains from the same location tend to be more similar than two strains for different countries. This characteristic tends to also be influences by pig flow and herd management.

Proposed terminology

Betlach et al. propose to classify the different mycoplasms by their VNTR ( Variable Number Tandem Repeats )-type. In this terminology, the number of VNTRs found for two different surface proteins such as P97 and P146 would be used to identify the microorganism. Lastly, the authors make a call for the creation of a tool to illustrate differences and relations between VNTR-types as well as the creation and curation of a public database to inventory them all.


Mycoplasma hyopneumoniae (M. hyopneumoniae) is the aetiologic agent of enzootic pneumonia in swine, a prevalent chronic respiratory disease worldwide. Mycoplasma hyopneumoniae is a small, self‐replicating microorganism that possesses several characteristics allowing for limited biosynthetic abilities, resulting in the fastidious, host‐ specific growth and unique pathogenic properties of this microorganism. Variation across several isolates of M. hyopneumoniae has been described at antigenic, proteomic, transcriptomic, pathogenic and genomic levels. The microorganism possesses a minimal number of genes that regulate the transcription process. Post‐translational modifications (PTM) occur frequently in a wide range of functional proteins. The PTM by which M. hyopneumoniae regulates its surface topography could play key roles in cell adhesion, evasion and/or modulation of the host immune system. The clinical outcome of M. hyopneumoniae infections is determined by different factors, such as housing conditions, management practices, co‐infections and also by virulence differences among M. hyopneumoniae isolates. Factors contributing to adherence and colonization as well as the capacity to modulate inflammatory and immune responses might be crucial. Different components of the cell membrane (i.e. proteins, glycoproteins and lipoproteins) may serve as adhesins and/or be toxic for the respiratory tract cells. Mechanisms leading to virulence are complex and more research is needed to identify markers for virulence. The utilization of typing methods and complete or partial‐gene sequencing for M. hyopneumoniae characterization has increased in diagnostic laboratories as control and elimination strategies for this microorganism are attempted worldwide. A commonly employed molecular typing method for M. hyopneumoniae is Multiple‐Locus Variable number tandem repeat Analysis (MLVA). The agreement of a shared terminology and classification for the various techniques, specifically MLVA, has not been described, which makes inferences across the literature unsuitable. Therefore, molecular trends for M. hyopneumoniae have been outlined and a common terminology and classification based on Variable Number Tandem Repeats (VNTR) types has been proposed.

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