Coxiella burnetii antigens for detection of Q fever antibodies by ELISA in human sera.

Different concentrations of chemically-treated (by potassium periodate oxidation or mild acid hydrolysis) purified phase I Coxiella burnetii (C.b.) corpuscles and natural (untreated) purified phase I and phase II C.b. corpuscles were compared by ELISA for detection of both phase I (directed to antigen 1) and phase II (directed to antigen 2) antibodies in human Q fever convalescent sera. As to the absorbance values the most sensitive was the antigen obtained by mild acid hydrolysis (0.1 mol/l HCl of phase I corpuscles for 30 min at 100 degrees C) followed by phase I corpuscular antigen (treated with 0.01 mol/l potassium periodate for 4 hr at 45 degrees C). The natural phase I (the 3rd egg passage) and phase II (the 162th egg passage) C.b. corpuscles gave lower absorbance with some sera not even distinguishing the 6th egg passage (EP6 or EP3 in phase I) from EP 162 or from negative controls.