DNA probes for the identification of Coxiella burnetti strains.

Isolation of Coxiella Burnetii in the standard laboratory setting is hazardous; therefore most diagnoses are based on retrospective detection of a rising antibody titer to C. burnetti. As a result, this disease is usually undiagnosed or misdiagnosed. Methods for the rapid detection of C. burnetti have now been developed that utilize specific hybridization of labeled DNA probes to nucleic acid in clinical samples. One method detects the presence of C. burnetii 16S ribosomal RNA (rRNA); another uses plasmid sequences. We have developed a probe that detects C. burnetii and one that differentiates between Coxiella strains capable of causing chronic disease and those that cause the acute form. Using these probes, C. burnetii can be identified in blood, urine, and tissue samples. The plasmid-derived probes detect as few as 10(4) organisms and less than 1 ng of Coxiella DNA. A third method differentiates between chronic (endocarditis-causing) strains and those that cause acute Q fever. This method uses the polymerase chain reaction (PCR), in which the target regions of DNA are amplified by iterative cycles of Taq I DNA polymerase chain extension to produce up to a 10(6) amplification of the target sequences. When Southern blotting is used in conjunction with PCR, the test detects as few as 2-9 C. burnetti cells.