Macrophage infectivity potentiator protein, a peptidyl prolyl cis-trans isomerase, essential for Coxiella burnetii growth and pathogenesis

Author summaryThe bacterium Coxiella burnetii is a highly infectious organism that is found worldwide and can cause debilitating disease in both animals and humans. Treatment of chronic infections remains very difficult and therefore it is essential to identify new drug targets to treat this infection. The Macrophage infectivity potentiator (Mip) protein has been reported as an attractive anti-virulence target in several pathogenic bacteria but its role has not been investigated in C. burnetii. This study demonstrates that inhibitors of the Mip protein from C. burnetii reduce replication inside host cells, increase the sensitivity of the bacteria to oxidative stress, and exhibit antibiotic properties against both the virulent and avirulent forms of C. burnetii. Furthermore, using a moth larvae infection model, the inhibitors demonstrated protective activity. These results suggest that, unlike other studied bacterial pathogens, C. burnetii requires Mip for replication, and that the further development of potent inhibitors against Mip offer potential as novel therapeutics to treat this infection. Coxiella burnetii is a Gram-negative intracellular pathogen that causes the debilitating disease Q fever, which affects both animals and humans. The only available human vaccine, Q-Vax, is effective but has a high risk of severe adverse reactions, limiting its use as a countermeasure to contain outbreaks. Therefore, it is essential to identify new drug targets to treat this infection. Macrophage infectivity potentiator (Mip) proteins catalyse the folding of proline-containing proteins through their peptidyl prolyl cis-trans isomerase (PPIase) activity and have been shown to play an important role in the virulence of several pathogenic bacteria. To date the role of the Mip protein in C. burnetii pathogenesis has not been investigated. This study demonstrates that CbMip is likely to be an essential protein in C. burnetii. The pipecolic acid derived compounds, SF235 and AN296, which have shown utility in targeting other Mip proteins from pathogenic bacteria, demonstrate inhibitory activities against CbMip. These compounds were found to significantly inhibit intracellular replication of C. burnetii in both HeLa and THP-1 cells. Furthermore, SF235 and AN296 were also found to exhibit antibiotic properties against both the virulent (Phase I) and avirulent (Phase II) forms of C. burnetii Nine Mile Strain in axenic culture. Comparative proteomics, in the presence of AN296, revealed alterations in stress responses with H2O2 sensitivity assays validating that Mip inhibition increases the sensitivity of C. burnetii to oxidative stress. In addition, SF235 and AN296 were effective in vivo and significantly improved the survival of Galleria mellonella infected with C. burnetii. These results suggest that unlike in other bacteria, Mip in C. burnetii is required for replication and that the development of more potent inhibitors against CbMip is warranted and offer potential as novel therapeutics against this pathogen.