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J Bacteriol Virol. 2016 Dec;46(4):275-282. English.
Published online December 31, 2016.  https://doi.org/10.4167/jbv.2016.46.4.275
Copyright © 2016 The Korean Society for Microbiology and The Korean Society of Virology
Isolation and Genetic Characterization of Orientia tsutsugamushi from Scrub Typhus Patients in Gyeongsangnam-do, Korea
Jong-Hun Ha,1 Dong-Hae Lee,1 Jin-Sik Park,1 Oh Hyun Cho,2 Dong-Hoon Kim,3 Na-Young Ha,4 Nam-Hyuck Cho,4 Kyu Jam Hwang,5 Yong-Gon Cho,6 Hye-Soo Lee,6 Won Kil Lee,7 Yoo Chul Lee,8 Myung-Je Cho,1 Woo-Kon Lee,1 and Min-Kyoung Shin1
1Department of Microbiology, Gyeongsang National University School of Medicine, Jinju, Korea.
2Department of Internal Medicine, Gyeongsang National University School of Medicine, Jinju, Korea.
3Department of Emergency Medicine, Gyeongsang National University School of Medicine, Jinju, Korea.
4Department of Microbiology and Immunology, Seoul National University College of Medicine, Seoul, Korea.
5Pathogen Resource TF, Center for Infectious Diseases, Korea National Institute of Health, Korea Center for Disease Control and Prevention, Cheongju, Korea.
6Department of Laboratory Medicine, Chonbuk National University Medical School, Jeonju, Korea.
7Department of Laboratory Medicine, Kyungpook National University School of Medicine, Daegu, Korea.
8Department of Microbiology, Kyungpook National University School of Medicine, Daegu, Korea.

Corresponding author: Woo-Kon Lee. Department of Microbiology, Gyeongsang National University School of Medicine, 816-15, Jinju-daero Jinju, Gyeong-Nam 52727, Korea. Phone: +82-55-772-8083, Fax: +82-55-772-8089, Email: wklee@gnu.kr Corresponding author: Min-Kyoung Shin. Department of Microbiology, Gyeongsang National University School of Medicine, 816-15, Jinju-daero Jinju, Gyeong-Nam 52727, Korea. Phone: +82-55-772-8081, Fax: +82-55-772-8089, Email: mkshin@gnu.kr
Received December 05, 2016; Revised December 07, 2016; Accepted December 07, 2016.

This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/).


Abstract

Orientia tsutsugamushi (O. tsutsugamushi), which is endemic to an Asia-Pacific region, has increased its incidence and caused annually around 10 thousand patients infected with scrub typhus in Korea in the past several years. In the present study, we isolated 44 O. tsutsugamushi from the patients with febrile illness accompanied with or without an eschar in Gyeongsangnam-do, Korea. These isolates were characterized by genetic analysis of the major outer membrane protein, the 56-kDa type-specific antigen (tsa56), which is unique to O. tsutsugamushi. Two types of sequences of tsa56, designated by JJ1 and JJ2, were determined from 37 and 7 isolates of the 44 isolates, respectively. JJ1 and JJ2 showed 74.7~90.8% identity in nucleotide sequence and 66.1~90.5% identity in amino acid sequence with 33 reference strains except for Boryong and Kuroki. JJ1 and JJ2 had 100 and 99.9% nucleotide identity to Boryong strain, and 99.9 and 99.8% to Kuroki, which has been known to be similar to Boryong, respectively. In addition, they showed 77.9~ 81.4% nucleotide identity with the cluster of Gilliam-related genotypes, whereas they showed higher nucleotide identity (89.6~90.8%) with the cluster of Karp-related genotypes. To our knowledge, this is the first report to isolate O. tsutsugamushi and characterize their genotype as the Boryong in Jinju and West Gyeongsangnam-do, Korea, even though it has been reported that the Boryong was the predominant genotype in isolates from chiggers, domestic rodents, and patients in the southern part of Korea. Furthermore, our isolates could be useful source to study on the pathophysiology and epidemiology of scrub typhus in Korea.

Keywords: Scrub typhus; Orientia tsutsugamushi; 56-kDa type-specific antigen; tsa56; West Gyeongsangnam-do

INTRODUCTION

Scrub typhus is an acute febrile disease caused by infection with Orientia tsutsugamushi (O. tsutsugamushi), which is transmitted by a trombiculid mite (1). It is characterized by fever with eschar as a pathognomonic sign and accompanied by other non-specific clinical signs such as headache, chills, cough, myalgia, conjunctival injection and skin rash, and sometimes serious complications such as meningitis, disseminated intravascular coagulation and multi organ failure (2, 3). The prevention of scrub typhus via mechanical control such as avoiding mite bites is the best because there is no available vaccine, and infection may be fatal without aggressive medical treatment (4). Genotypes of O. tsutsugamushi strains were classified according to the diversity of outer membrane protein 56-kDa type-specific antigen (tsa56): Gilliam, Karp, Kato, Kawasaki, Kuroki, Shimokoshi, Boryong, Yonchon, and so on (3). The tsa56, which is essential to attach and penetrate to cells, has four variable domains I - IV and they show genotypes specificity (5, 6). Virulence of O. tsutsugamushi for humans varies depending on its genotypes. Therefore, the surveillance of geographical distribution of O. tsutsugamushi genotypes has been continuously performed.

O. tsutsugamushi is endemic to the geographical triangle, called as a tsutsugamushi triangle, of an Asia-Pacific region covering from northern Japan in the east to Pakistan in the west and northern Australia in the south (3, 7). The distribution of genotypes varies geographically. The Gilliam, Karp, Kato, TA678, Ta686, TA716, TA763, and TH1817 have been identified in Thailand, Malaysia, Philippines, and Australia (6). The Gilliam, Karp, Kato, Kawasaki, Shimokoshi, Irie, and Hirano were identified in Japan (6). TA716 and Gilliam were predominant in Australia and Russia, respectively (8). Meanwhile, the Karp and TA716 were predominant in Taiwan (8). The Boryong was the most common in southern part of Korea, but Karp and Gilliam were identified in northern and central part of Korea (6). O. tsutsugamushi isolates from chigger mites, field rodents, and human were identified as the Boryong in Gyeongsangnam-do, the southern part of Korea according to the reports of Chang et al. and Ree et al. in 1999 and 2001 (6, 9). Even though the Boryong shows 99.9% homology of the nucleotide and amino acid sequences of tsa56 variable domain in comparison with the Kuroki, it has different features from the Kuroki in terms of virulence in mice and reactivity to KP10, a Karp-specific monoclonal antibody (2). In the present study, we isolated 44 O. tsutsugamushi from the patients with scrub typhus in Jinju, Korea and characterized their genotypes using tsa56.

MATERIALS & METHODS

Isolation and identification of O. tsutsugamushi from the patients with scrub typhus

O. tsutsugamushi isolates used in this study were obtained from National Culture Collection for Pathogens (NCCP, Cheongju, Korea). O. tsutsugamushi isolates were isolated and identified from the patients enrolled in Gyeongsang National University Hospital, Gyeongsangnam-do, Korea in 2015 as follows: Blood samples were drawn from the patients who had high fever and an eschar in 2015. Buffy coat was collected after centrifugation at 3,000 rpm for ten min and inoculated into L-929 (mouse fibroblast) cell culture. The inoculated cells were incubated in the presence of 5% CO2 at 37℃ for one half-hour, and then washed with Dulbecco's phosphate buffered saline (DBPS; Gibco BRL Co., Gaithersburg, USA) after removal of the supernatant. The infected cells were maintained with media change twice a week under conditions of 5% CO2 at 35℃ until the cytopathic effect appeared. Orientia infection was identified using indirect immunofluorescence assays (IFA) and PCR and sequencing for tsa56, as previously described (10, 11). For IFA, the infected cell culture prepared on slide glass were diagnosed using pooled serum from ten patients with scrub typhus whose IFA titers were more than 1:128. After O. tsutsugamushi was identified by IFA, the cells were detached using a scraper, and stored at - 80℃. All the isolates identified were then deposited at NCCP.

Amplification and sequencing of the tsa56

Amplification reactions of tsa56 were performed using genomic DNA, which was extracted from the infected L-929 cell using DNeasy tissue kits (QIAGEN, Hilden, Germany) according to manufacturer's protocol. The primer set for tsa56 gene are p33 (forward): 5'-TCAAGCTTATTGCTAGTGCAATGTCTGC-3', and p55 (reverse): 5'-AGGGATCCCTGCTGCTGTGCTTGCTGCG-3' according to the method of Furuya et al. (11). The PCR was performed as the following conditions: an initial denaturation step at 94℃ for 7 min was followed by 35 cycles of 94℃ for 1 min, 57℃ for 1 min, and 72℃ for 1 min, and then a final incubation step of 72℃ for 10 min. The PCR products were purified using the GeneAll PCR SV (GeneAll, Seoul, Korea) and sequenced using automatic dye terminator DNA sequencing (Thermo Fisher Scientific, Waltham, USA).

Phylogenetic analysis

The sequence data were aligned with reference sequences of tsa56 in the BLASTN database (National Center for Biotechnology Information) using MegAlign 5.0 DNASTAR (DNASTAR Inc., Madison, USA). Nucleotide identity of the gene was calculated on the basis of pairwise comparison using Lasergene, 5.0 DNASTAR. Phylogenetic relationships were generated via Neighbor-joining methods, bootstrap analysis (500 repeats) using MEGA software (version 6.0, Arizona State University, Tempe, USA).

RESULTS & DISCUSSION

As shown in Fig. 1, the total number of the scrub typhus patients diagnosed in Gyeongsang National University Hospital increased since 2013, even though the number of patients decreased somewhat in 2014. The incidence was focused on from October to December, and was the highest in November. Ninety-four cases were diagnosed or suspected as incidence of the scrub typhus from the patients with acute febrile illness with or without eschar in 2015. Among the ninety-four cases, blood samples were collected from 57 patients and 44 isolates of O. tsutsugamushi were finally obtained and deposited at NCCP.


Figure 1
The incidence of the scrub typhus patients of Gyeongsang National University Hospital in 2013 to 2015.
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Forty-four isolates from Gyeongsangnam-do in 2015 were obtained from NCCP, and the identification was confirmed by PCR amplification of tsa56, which was predicted to be a length of 1,028-bp (Fig. 2). A total 44 isolates were obtained from 26 women and 18 men. In addition, age distribution of the scrub typhus patients was 10~80 years. The number of patients for each age group is as follows: 10s, 1; 30s, 1; 40s, 1; 50s, 10; 60s, 6; 70s, 20; and 80s, 5.


Figure 2
The PCR products of the 56-kDa type-specific antigen gene of O. tsutsugamushi from 15 representative isolates in the present study. Forty-four O. tsutsugamushi isolates were confirmed by tsa56-specific PCR assay, and PCR products of 15 representative isolates among 44 isolates were presented. M, DNA sizer marker.
Click for larger image

In the present study, nucleotide sequence of tsa56 from 44 isolates, which is a species-specific marker gene of O. tsutsugamushi was divided into two types, JJ1 and JJ2. JJ1 and JJ2 were determined from 37 and 7 isolates, respectively. Therefore these two sequences and 35 reference sequences of tsa56 were enrolled in the nucleotide and amino acid identity analysis and phylogenetic analysis. JJ1 and JJ2 showed 74.7~90.8% nucleotide identity and 66.1~90.5% amino acid identity with 33 reference sequences except for Boryong and Kuroki. Since both Boryong and Kuroki strains showed 100% and 99.9% nucleotide identities with JJ1 and 99.9% and 99.8% to JJ2, they were clustered within the same phylogenic tree (Table 1 and Fig. 3). In addition, they showed 77.9~81.4% nucleotide identity with the cluster of Gilliam-related genotypes consisting of FPW2016, Gilliam, Ikeda, Kawasaki, TW461, UT125, UT144, UT196, and Yonchon, whereas they showed higher nucleotide identity (89.6~90.8%) with the cluster of Karp-related genotypes consisting of Hirahata, Je-cheon, Karp, LA-1, TW45R, UT176, UT177, Yeojoo (Table 1 and Fig. 3).


Figure 3
Phylogenetic tree based on partial 56-kDa type specific antigen of O. tsutsugamushi. Two nucleotide sequences of O. tsutsugamushi isolates were analyzed phylogenetic relationship with reference sequences retrieved from the GenBank database as shown in Table 1. Solid triangle and diamond indicate two sequences of O. tsutsugamushi determined in this study.
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Table 1
Sequence homologies of partial 56-kDa type specific antigen gene between Orientia tsutsugamushi strains
Click for larger image

In the previous report, Chong et al. isolated 11 strains of O. tsutsugamushi from scrub typhus patients in Jinhae, which is central area of Gyeongsangnam-do and identified 10 of them as the Karp type based on the indirect immunoperoxidase test with monoclonal antibodies specific to Gilliam, Karp or Kato strain (12). Even though they were reported as Karp type in 1989, they could be considered the Boryong type since the Boryong was determined as a new type in 1990. Moreover, most O. tsutsugamushi isolates from chigger and rodents in Gyeongsangnam-do have identified as the Boryong. The fact that the amino acid identities of JJ1 and JJ2 are the highest in the comparison with the Karp type (84.6%) among the three original prototypes (Gilliam, Karp and Kato) in this study (Table 1) can partially explain the reason why they were identified as the Karp type serologically in the previous report.

To our knowledge, this is the first report to isolate O. tsutsugamushi characterized as their genotypes to the Boryong in Jinju and nearby area, Gyeongsangnam-do, Korea, even though it has been reported that the Boryong was the predominant genotype isolated from chiggers, domestic rodents, and patients in the southern part of Korea. Our isolates could be useful source for microbiological and epidemiological study on O. tsutsugamushi infection in Korea.

Notes

The pathogen resources for this study were provided by Gyeongsang National University Hospital (GNUH), as the Branch of National Culture Collection for Pathogens (NCCP). This research was supported by the National Culture Collection for Pathogens (NCCP) R&D project of the Ministry of Health & Welfare (2015-ER4701-00).

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