Hemotrophic mycoplasmas (HM) are uncultivable bacteria found on and in the red blood cells (RBCs). The main clinical sign of HM infections is the hemolytic anemia. However, anemia-inducing pathogenesis has not been totally clarified. In this work we used the splenectomized pig as animal model and Mycoplasma suis as a representative for hemotrophic mycoplasmas to study anemia pathogenesis. Eryptosis, i.e. programmed cell death of RBCs, is characterized by cell shrinkage, microvesiculation and phosphatidylserine (PS) exposure on the outer membrane. The eryptosis occurrence and its influence on anemia pathogenesis was observed over the time-course of M. suis infections in pigs using 3 M. suis isolates of differing virulence. All 3 isolates induced eryptosis, but with different characteristics. The occurrence of eryptosis could as well be confirmed in vitro: serum and plasma of an acutely ill pig induced PS exposure on erythrocytes drawn from healthy pigs. Since M. suis is able to induce eryptotic processes it is concluded that eryptosis is one anemia-inducing factor during M. suis infections and, therefore, plays a significant role in the pathogenesis of infectious anemia due to HM infection.

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Mycoplasma suis belongs to the haemotrophic mycoplasmas which colonise red blood cells of a wide range of vertebrates. Adhesion to red blood cells is the crucial step in the unique lifecycle of M. suis. Due to the lack of a cultivation system, identification of adhesion structures has been difficult. So far, only one adhesion protein, i.e. MSG1 was identified. In order to determine further adhesion molecules of M. suis, we screened genomic M. suis libraries and performed Southern blot hybridisation analyses of genomic M. suis DNA. The -enolase of M. suis was identified and analysed genetically and functionally. The encoding gene has 1623bp in size. The deduced amino acid sequence showed an overall identity of 59.6-65.1% to -enolases of other pathogenic mycoplasmas. The 540aa M. suis -enolase displays a size extension of about 90aa in comparison to -enolases of other mycoplasmas. Recombinant -enolase expressed in Escherichia coli demonstrated immunogenicity in experimentally infected pigs. Immunoblot, confocal laser scanning microscopy and immune electron microscopy analysis using antibodies against recombinant -enolase, indicate the membrane and surface localisation of native -enolase in M. suis, though no typical signal sequences exist. Furthermore, we showed that recombinant -enolase binds to porcine erythrocyte lysate in a dose-dependent manner. E. coli transformants which express -enolase on their surface acquire the ability to adhere to porcine red blood cells. In conclusion, our observations indicate that -enolase could be involved in the adhesion of M. suis to porcine red blood cells.