Introduction

Rodentibacter heylii (R. heylii) is a frequently detected pathogen causing pneumonia, abscesses and mastitis in laboratory mice. In a recent infection experiment, we observed an unexpected high virulence of a strain not harboring any known virulence-associated factor. Furthermore, efficient colonization of the upper respiratory tract was detected 28 days after experimental infection. In R. heylii, three RTX-Proteins are described. However, the used strain harbors none of these known virulence factors, suggesting that an unknown virulence factor must be expressed by this strain.

Goals

Aim of this study was to identify a new potential virulence factor crucial for the pathogenesis of bronchopneumonia caused by R. heylii.

Materials and Methods

Immunogens of R. heylii strain were identified via immunoproteomics. Using an RhiA-specific IgY, flowcytometry and immunohistochemistry were conducted to evaluate the in vitro and in vivo expression of RhiA. Further experiments are in progress to characterize RhiA functionally.

Results

Sera from convalescent mice were immunoreactive to a specific band of a protein extract from R. heylii labeled to an SDS-Page. The corresponding protein was identified and designated as R. heylii immunogen A (RhiA). Flow cytometry confirmed expression on the bacterial surface in vitro, indicating that RhiA is a surface-associated protein. Immunohistochemistry showed that RhiA is expressed in vivo in association with putative bacterial biofilms on epithelial surfaces in bronchioli and alveoli after experimental infection. In silico analysis revealed similarity to a TISS secreted RTX agglutinin of a different strain in the family of Pasteurellaceae (NI1060).

Summary and Outlook

RhiA is an immunogenic protein, which is associated to the bacterial surface and expressed in vivo during infection. Similarities to known RTX-proteins suggests, that it is a new potential virulence factor. Further a deletion mutant of the used R. heylii strain without RhiA should be constructed by Crispr/Cas to analyze the function of RhiA. Therefore, several in vitro assays including adherence and biofilm formation followed by in vivo studies will be conducted.