Ann Lab Med 2020; 40(5): 370-381
Clonal Distribution of Clindamycin-Resistant Erythromycin-Susceptible (CRES) Streptococcus agalactiae in Korea Based on Whole Genome Sequences
Takashi Takahashi, M.D., Ph.D.1, Takahiro Maeda, B.P.1, Seungjun Lee, M.D.2, Dong-Hyun Lee, M.D.3, and Sunjoo Kim, M.D., Ph.D.2,4
1Laboratory of Infectious Diseases, Graduate School of Infection Control Sciences & Kitasato Institute for Life Sciences, Kitasato University, Tokyo, Japan; 2Department of Laboratory Medicine, Gyeongsang National University Changwon Hospital, Changwon, Korea; 3Department of Laboratory Medicine, Gyeongsang National University Hospital, Jinju, Korea; 4Department of Laboratory Medicine, Gyeongsang National University College of Medicine, Institute of Health Sciences, Jinju, Korea
Corresponding author: Sunjoo Kim, M.D., Ph.D.
Department of Laboratory Medicine, Gyeongsang National University Changwon Hospital, 11 Samjungja-ro, Seongsan-gu, Changwon 51472, Korea
Tel: +82-55-214-3072
Fax: +82-55-214-3087
Received: December 23, 2019; Revised: January 17, 2020; Accepted: March 27, 2020; Published online: September 1, 2020.
© Korean Society for Laboratory Medicine. All rights reserved.

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Background: The clindamycin-resistant erythromycin-susceptible (CRES) phenotype is rare in Streptococcus agalactiae (group B streptococci). We aimed to determine the molecular characteristics of CRES S. agalactiae using whole genome sequencing (WGS).
Methods: Sixty-six S. agalactiae isolates obtained from blood (N=26), cerebrospinal fluid (N=10), urine (N=17), and vaginal discharge (N=13) between 2010 and 2017 in Korea were subjected to WGS. Based on the WGS data, we analyzed antimicrobial resistance (AMR) determinants, sequence types (STs), capsular polysaccharide (CPS) genotypes, and virulence gene profiles, and constructed a phylogenetic tree. We included the clindamycin-susceptible erythromycin-resistant (CSER) phenotype for comparison.
Results: We identified seven CRES S. agalactiae isolates from urine (N=5) and vaginal discharge (N=2) collected between 2010 and 2011. All CRES isolates harbored AMR determinants of lnu(B), lsa(E), and aac(6’)-aph(2’’), revealed ST19 and CPS genotype III, and had a virulence gene profile of rib-lmb-cylE. Phylogenetic tree analysis revealed that all CRES isolates belonged to the same cluster, suggesting a clonal distribution. In contrast, seven CSER isolates showed a diverse distribution and clustered separately from the CRES isolates.
Conclusions: CRES isolates collected between 2010 and 2011 showed a unique cluster with ST19 and CPS genotype III in Korea. This is the first report on WGS-based characteristics of S. agalactiae in Korea.
Keywords: Streptococcus agalactiae, Group B streptococci, Antimicrobial resistance, Whole genome sequencing, Sequence types, Clonal distribution, CRES (clindamycin-resistant erythromycin-susceptible)

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