The Role of International Travellers in the Spread of CTX-M-15-producing Shigella Sonnei in the Republic of Korea

Background: Multidrug-resistant Shigella isolates have recently emerged as a serious public health threat worldwide. In particular, overseas travel is a risk factor for acquisition of antimicrobial-resistant Shigella strains. To explore the role of travel in the spread of cefotaxime-resistant Shigella sonnei in Korea, we screened 751 Shigella spp. isolates from 2007 to 2016 through the National Surveillance system, and 28 cephalosporin-resistant S. sonnei isolates were identified. Methods: For cephalosporin-resistant S. sonnei isolates, epidemiological and molecular analyses (plasmid structure analysis, pulsed-field gel electrophoresis (PFGE) and high-quality single-nucleotide polymorphisms (hqSNPs) based on whole-genome sequencing (WGS)) were conducted to investigate the source of infection and transmission route. Results: Among the 28 cefotaxime-resistant S. sonnei strains, 18 were isolated from travellers returning from Asia, including Vietnam (n = 11). Molecular analysis of 18 bla(CTX-M)-type isolates revealed that 15 contain CTX-M-15; 50% of isolates from domestic patients contain CTX-M-14. Analysis of the genetic environments of the bla(CTX-M-14) and bla(CTX-M-15) genes revealed different genetic organization surrounding the bla(CTX-M) genes. Additionally, PFGE and hqSNP results suggested a large phylogenetic distance between the S. sonnei isolates related to overseas travel and those acquired domestically in Korea. Conclusion: Our study data demonstrates that two prevalent bla(CTX-M) genes, bla(CTX-M-14) and bla(CTX-M-15), have been circulating in S. sonnei in Korea over the last 10 years. Recently, international travellers are at a high risk for acquisition of CTX-M-15-producing S. sonnei in Korea. (C) 2019 Published by Elsevier Ltd on behalf of International Society for Antimicrobial Chemotherapy.