Reorganization of actin cytoskeleton in L929 cells infected with Coxiella burnetii strains isolated from placenta and foetal brain of sheep (Sardinia, Italy)

Coxiella burnetii, the etiological agent of Q Fever, is a zoonotic pathogen distributed worldwide. It has been reported that virulent strains of C. burnetii are poorly internalized by monocytes compared to avirulent variants. Virulence is also associated to the formation of pseudopodal extensions and transient reorganization of filamentous actin. In this article, we investigated the ability of 2 Coxiella strains isolated from ovine aborted samples to induce reorganization of the actin cytoskeleton in mouse fibroblast cells. Cells were exposed for 24 and 48 hours to ovine placenta and foetal brain tissue homogenates and then analysed by polymerase chain reaction (PCR) in order to detect Coxiella infection. The formation of pseudopodal extensions, the polarized distribution of F-actin, and the involvement of C. burnetii strain in cytoskeleton reorganization have been assessed using a laser scanning confocal fluorescence microscope. Results indicate that similarly to the virulent reference strain, strains of C. burnetii isolated from foetal brain induced morphological changes – modification in F-actin distribution and in the localization of bacteria. By contrast, C. burnetii strain isolated from ovine placenta did not induce any significant change in L929 cell morphology. In conclusion, both C. burnetii strains isolated from ovine placenta and foetal brain were pathogenic causing ovine abortion, but in vitro the C. burnetii strain isolated from brain only was able to induce F-actin reorganization in L929 infected cells.