Epidemiologic analysis of Shigella sonnei Isolates by using Antimicrobial Resistance Gene Probes

Seol, Sung Yong; Jeong, Young Sook; Kang, Hee Young; Yu, Hak Sun; Lee, Yoo Chul; Cho, Dong Taek

Abstract

Thirty-four Shigella sonnei isolates from 6 outbreaks and sporadic cases from May 1999 until January 2000 in Daegu and 9 regions of Gyeongsangbuk-Do were epidemiologically analyzed by plasmid profiling, pulsed-field gel electrophoresis (PFGE), and hybridization with 2 antimicrobial resistance gene probes, tetA and dfrA1. In outbreak cases, resistance pattern in all of the strains was identical: they were resistant to tetracycline (Tc), streptomycin (Sm), sulfisomidine (Su), trimethoprim (Tp), and nalidixic acid (Na). In sporadic cases, Tc, Sm, Su, Na, ampicillin (Ap), and kanamycin (Km) pattern and TcSmSuTpApNa pattern were additionally observed. Isolates from the same outbreak showed identical plasmid profile and PFGE pattern. Most of different outbreak strains and sporadic strains showed different plasmid profiles, and identical or different PFGE patterns, while all of the isolates shared common tetA gene on a non-conjugative 18.3 kbp R plasmid carrying resistance to tetracycline, streptomycin, and sulfisomidine, and dfrA1 gene on the chromosome. Non-conjugative R plasmids derived from all of the isolates were confirmed to be identical by the Southern hybridization analysis of restriction endonuclease treated or non-treated plasmid profiles using the tetA probe. The same strains also reacted with dfrA1 probe at the same-sized DNA fragment (60 kbp) on pulsed-field gel electrophoresis of total genomic DNA. Our findings suggested that epidemic strains of Shigella sonnei prevalent in the Daegu and Gyeongsangbuk-Do area during the test period should have originated from an identical or closely related strain source although most of strains did not show the same plasmid profile and PFGE pattern.