Identification of spotted fever group Rickettsia species by polymerase chain reaction-restriction fragment length polymorphism analysis of the sca4 gene.

DNA samples from four rickettsial species in Japan--R. japonica Aoki, R. asiatica IO-1, R. helvetica IP-1, and Rickettsia tamurae AT-1--were analyzed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) in which a portion of the sca4 gene was amplified and restriction digested with the MspI enzyme. Each spotted fever group rickettsial species exhibited unique restriction profiles after MspI digestion. To examine the possibility of applying PCR-RFLP analysis to field samples, 36 Ixodes persulcatus ticks were collected from the Tokachi region (Hokkaido, Japan) by the flagging method and subjected to PCR-RFLP analysis. Of the ticks collected, five had identical restriction profiles to that of R. helvetica. Amplification and sequencing of the gltA gene for two of the five positive samples revealed that the sequences were identical to that of the Rickettsia sp. Tokachi-B-IP17m, which exhibits the highest similarity to R. helvetica. These results demonstrate that PCR-RFLP analysis is useful for identifying Rickettsia species in Japan and is applicable to epidemiological studies involving tick samples.