Quantification of Rickettsia australis.

Several assay systems were compared for measuring the concentration of viable Rickettsia australis, including embryonated eggs, tissue cultures, and mouse inoculation. Direct rickettsial counts that included the enumeration of both viable and nonviable rickettsiae were used to obtain baseline values. Assays were conducted in parallel using serially diluted R. australis preparations to establish which assay displayed the greatest sensitivity and reproducibility. Overall, the plaque assay using buffalo green monkey kidney cells with centrifugation of the rickettsiae onto the monolayers was the most sensitive assay for detecting R. australis, while the embryonated egg assay and mouse lethality titrations were the least sensitive.