Abstract: Objectives: To Investigate the change in Antibiotic resistance and carriage of class 1 and class 2 integrons of shigella isolates in Tianjin,China.Methods: A total of 57 clinical isolates of shigella identified in Tianjin during the years 1981–1983 and 2009 were studied.Antibiotic susceptibility were detected by K-B disk diffusion method .Carriage of class 1 and class 2 integrons was investigated by polymerase chain reaction (PCR) with specific primers and confirmed by restriction endonuclease analysis of amplicons.Results:In the group duing the years 1981–1983 ,Class 1 integrons were found in 87.88%(29/33) of Shigella isolates.27 of these integron 1-positive isolates contained gene cassette aadA which confer resistance to streptomycin.Only the Shigella sonnei isolates contained gene cassette dfrA17+aadA5 which confer resistance to trimethoprim and streptomycin.None integron 2-positive isolates were found;In the other group duing the years 2009,Class 1 integrase were found in 79.17%(19/24) of Shigella isolates,however,variable region and 3'conserved segment of class 1 integron were negative in all isolates. Class 2 integrons were present in 87.50%（21/24）of the Shigella isolates. All of these integron 2-positive isolates contained constant gene cassette arrays of dfrA1+sat1+aadA1 which confer resistance to trimethoprim,streptothricin and streptomycin.Both class 1 and class 2 integrase were present in 17 shigella isolates.Conclusions: Antibiotic resistance have been developed in the evolution of Shigella strains;Integron carriage were very common among the shigella isolates.

Key words: Integrons, shigella, drug-resistance