Chlamydia suis causes reproductive failure, conjunctivitis, enteritis and pneumonia in pigs. Tetracycline resistant C. suis strains are emerging. The infection is transmittable to humans as we recently isolated C. suis from the eyes of abattoir personnel. There is no vaccine. There are biological differences between C. suis strains. Recently, we annotated the genome of a C. suis strain which caused severe economic loss due to reproductive failure in sows. We found the family of polymorphic membrane proteins (Pmps) that likely play an important role in disease pathogenesis as they might contribute to the biological differences observed for C. suis strains. Pmps might play a role in adhesion of the bacterium to the host cell as well as in tissue tropism and transfer to humans. Pmps might cause inflammation, contributing to the development and progression of lesions. The project aims at: 1) genome sequencing of biologically different C. suis strains, 2) studying the phylogenetic diversity of C. suis isolates by multi locus sequence typing (MLST), analysis of the variable number of tandem repeats (VNTR) and outer membrane protein A (ompA) gene sequencing, 3) functional analysis of the Pmps of genetically and biologically different C. suis strains and finally, 4) determination of the Pmp profile in relation to tissue tropism. Fulfilment of the objectives will enable: (i) more effective disease prevention using the results from the proposal for development of vaccines based on a combination of Pmps, (ii) detection and differentiation of C. suis strains in relation to tissue tropism/virulence by newly developed nucleic acid amplification assays, (iii) treatment and epidemiological surveillance in both pigs and humans.