Comparison of serologic typing, sodium dodecyl sulfate-polyacrylamide gel electrophoresis protein analysis, and genetic restriction fragment length polymorphism analysis for identification of rickettsiae: characterization of two new rickettsial strains.

In 1990, 17 adult Rhipicephalus turanicus ticks were collected in the south of France. Two spotted fever group rickettsiae, Mtu1 and Mtu5, were isolated from the hemolymphs of two of these ticks by the centrifugation shell-vial technique by using HEL cells. These isolates were compared with reference spotted fever group rickettsial serotypes by using three identification methods: microimmunofluorescence serologic typing, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and polymerase chain reaction followed by restriction endonuclease fragment length polymorphism analysis. The results obtained by all these techniques showed that Mtu1 and Mtu5 are each previously undescribed rickettsial serotypes. A comparison of the three methods used to identify the isolates led us to the conclusion that, in large-scale epidemiological studies, the simplest way to identify isolates in ticks is to first use the polymerase chain reaction-restriction fragment length polymorphism analysis directly on triturated ticks as a screening method to detect interesting rickettsiae, and then attempt to isolate rickettsiae from ticks for identification by microimmunofluorescence and SDS-PAGE, both of which are time-consuming and expensive to carry out.