High prevalence of atypical class 1 integrons and class 2 integrons in multi-drug resistance Shigella flexneri isolated from China

Abstract

Shigella flexneri is an important cause of bacterial dysentery in the developing world. Treatment with most widely used and inexpensive antimicrobial drugs became limited due to globally emerging antimicrobial resistance. Integron-associated antibiotic resistance was observed in S. flexneri. This study described the antimicrobial susceptibility and the characteristic of classes 1 and 2 integrons in S. flexneri in China. 90.5% (48/53) S. flexneri strains accounted for multi-drug resistance and carried integrons of class 1 (90.5%), class 2 (86.8%), or both (86.8%). The gene cassettes of typical class 1 integrons, dfrV and dfrA17-aadA5, were detected in 6 strains and 2 strains, respectively. Atypical class 1 integrons with gene cassettes blaOXA-30-aadA1 were detected in 45 (84.9%) strains. The typical and atypical class 1 integrons coexisted in 6 strains; 46 (86.8%) strains carried class 2 integrons with gene cassettes dfrA1-sat1-aadA1. No intI3was detected. The PFGE profiles showed spread of integrons among different serotypes in S. flexneri. The majority of Shigella strains are resistant to ampicillin, chloramphenicol, tetracycline, streptomycin and trimethoprim-sulfamethoxazole. Atypical class 1 and class 2 integrons are widely present in these Shigella strains. Typical and atypical class 1 integrons coexist among some multi-drug resistant Shigella strains. Key words: Shigella flexneri, integrons, multi-drug resistance, pulsed-field gel electrophoresis.