Antimicrobial resistance patterns and characterization of integrons of Shigella sonnei isolates in Seoul, 1999-2008.

A total of 66 Shigella sonnei isolates from 1999 to 2008 in Seoul was analyzed for their antimicrobial resistance, carriage of integron, and the patterns of Pulsed-field gel electrophoresis (PFGE). A high level of antimicrobial resistance to streptomycin (100%), trimethoprim/sulfamethoxazole (95%), tetracycline (94%), nalidixic acid (65%), and ampicillin (41%) was observed among S. sonnei isolates. Fourteen profiles of antimicrobial resistance were identified with the most common resistance profile being nalidixic acid, streptomycin, tetracycline, and trimethoprim/sulfamethoxazole (35%). PCR and DNA sequencing analysis revealed the presence of class 2 integron in all isolates, and class 1 and 2 integrons in 7 isolates. The class 2 integron carried two types of gene cassettes. One cassette array was dfrI, sat2, and aadA1 (91%), and the other was dfr1 and sat1 (8%). dfrA12 and aadA2 gene cassette was found in one isolate containing class 1 integron. PFGE was carried out to examine the genetic relatedness among isolates. All isolates except for one showed similar PFGE patterns (similarity of 80.1%). These results suggest that the S. sonnei isolated during 1999-2008 in Seoul have similar lineages that have not undergone evolutionary changes with time.