New Genotypes and Diversity of Orientia tsutsugamushi Isolated from Scrub Typhus Patients in South Korea as Determined by Multilocus Sequence Typing

Orientia tsutsugamushi, an obligate intracellular organism, is the causative agent of scrub typhus, which is endemic in the Asia-Pacific region. No comparative studies on the genotypic properties of O. tsutsugamushi have been performed using multilocus sequence typing (MLST) in South Korea. Here, we characterized 51 clinical isolates from Jeonju, in southwestern Korea, and we compared them to isolates from Thailand, Laos, and Japan. We also identified 10 new alleles and six novel sequence types. Overall, our results suggest that the relative genetic stability and the clonal populations of O. tsutsugamushi strains in South Korea have remained mostly conserved. Author summaryScrub typhus is a life-threatening disease, caused by infection with O. tsutsugamushi, a Gram-negative intracellular bacterium. Approximately one million people are infected globally every year, especially in the Asia-Pacific region. Strains of O. tsutsugamushi are typically distinguished serologically on the basis of sequences of the highly polymorphic 56-kDa outer membrane protein. Multilocus sequence typing (MLST) is a generic typing method that provides a unified bacterial isolate characterization approach that can be used for evolutionary and population studies of bacteria. In this study, we describe the development and application of a MLST scheme that was applied to 51 O. tsutsugamushi isolates. We found 10 new alleles and six new STs, which yielded a total of seven O. tsutsugamushi STs in South Korea. Among seven different STs (ST 48, 93-98), ST 48 account for the largest proportion (49.0%) of O. tsutsugamushi STs in South Korea. With the exception of the appearance of six novel STs, the clonal populations have remained conserved but further study of population structure and evolutionary trends is warranted.