Assay of Coxiella Burnetii by Enumeration of Immunofluorescent Infected Cells

Abstract

A quantitative assay of Coxiella burnetii was developed based on immunofluorescent staining of infected L cell monolayers and enumeration of cells containing fluorescent rickettsial antigens within 48 hr after inoculation. Adsorption of rickettsiae onto coverslip cell cultures was accelerated and highly efficient when augmented by centrifugal force. By this procedure, a proportionality was demonstrated between the number of infected cells and the volume of inoculum. The incubation period of 48 hr for inoculated cell cultures was established from sequential observations of the development of rickettsial infection of cells and infected cell counts. The relationship between rickettsial concentration and cell-infecting units of rickettsiae was linear; the distribution of infected cells was random. The assay of C. burnetii by the infected cell-counting procedure was highly precise and sensitive.