Unraveling persistent host cell infection with Coxiella burnetii by quantitative proteomics

The interaction between the immune system and invading bacteria is sufficient to eradicate microorganisms for the majority of bacterial infections, but suppression of the microbicidal response leads to reactivation or chronic evolution of infections and to bacterial persistence. To identify the cellular pathways affected by bacterial persistence, we applied the MS-driven combined fractional diagonal chromatography (COFRADIC) proteomics technique for a comparative study of protein expression in the C. burnetii strains Nine Mile (NM) and its respective strain (NMper) isolated from 18 months persistently infected cell cultures. In total, three different proteome comparisons were performed with the total bacterial proteome, potentially secreted bacterial proteins, and the eukaryotic infected proteome being assessed. Our results revealed that among the 547 identified bacterial proteins, 53 had significantly altered levels of expression and indicated potential metabolic differences between the two strains. Regarding differences in the secreted proteins between both strains and different modulation of the host cell, machineries reflect at least large rearrangements of both bacterial and eukaryotic proteomes during the persistent model of infection when compared to the acute one, which emphasizes that C. burnetii orchestrates a vast number of different bacterial and eukaryotic host cell processes to persist within its host.