Analysis of Coxiella burnetii isolates in cell culture and the expression of parasite-specific antigens on the host membrane surface.

Coxiella burnetii isolates may be classified into several groups based on plasmid character. These groups may also be correlated with disease syndrome--chronic or short-term acute. L929 mouse fibroblast cells were exposed, independently, to two members of the three major C. burnetii groups, and their growth/morphological characteristics analysed by light and electron microscopy, including High Voltage Electron Microscopy. The fates of the isolates were followed. Two acute isolates [Nine Mile (RSA 493) and Henzerling (RSA 331), QpH1-type plasmids] and two chronic isolates (S Q217 and L Q216, plasmidless) readily infected L929 cells in static culture. Priscilla (Q177) and F (Q228) isolates (QpRS-type plasmid, and implicated in causing chronic Q fever) took longer to infect cells, and, unlike the members of the other two groups, gradually disappeared when shifted to suspension culture. Cells infected with Q177 and Q228 exhibited a higher degree of vacuolation than cells infected with the other isolates. Parasite-specific antigens on the surfaces of the host cells were analysed by immunofluorescence/flow cytometry. The acute and plasmidless isolates caused the display of significantly more C. burnetii-specific antigen on the host cell membrane than the two QpRS plasmid-containing isolates. This host cell model system clearly reveals biological differences among the C. burnetii groups.