Background and objective: Coxiella burnetii is the bacterial causative agent of Q fever in humans. Because Q fever can establish itself with an initial inoculation of fewer than ten C. burnetii cells, a sensitive detection method for C. burnetii infection is needed for early detection. We aimed to evaluate the effectiveness of a complementary locked primer (CLP)-based real-time PCR method for sensitive detection of C. burnetii infection.
Methods: To evaluate the ability of CLPs to enhance the efficiency of the real-time PCR assay for the C. burnetii IS1111 insertion sequence, the mean threshold cycle values from 20 real-time PCR replicates with either CLPs or conventional primers were determined using tenfold serial dilutions (102-108) of purified C. burnetii Nine Mile genomic DNA. In addition, the cross-reactivity between C. burnetii and 31 non-Coxiella species was examined.
Results: The CLP-based real-time PCR allowed specific and reliable detection of as few as 59 copies of the IS1111 element present in the genome of C. burnetii, which represents approximately 2.96 genome equivalents or three cells of C. burnetii. These results demonstrate the effectiveness of CLP-based real-time PCR for sensitive detection of C. burnetii infection.
Conclusion: It can be concluded that the CLP-based real-time PCR assay is a more appropriate method for sensitive detection and quantification of C. burnetii than previously reported methods.