Molecular characterization of integron gene cassettes in Escherichia coli strains isolated from blood cultures

Antibiotics are known to play a very important role in human health. However, incorrect and excessive use leads to multiple antibiotic resistance of many bacteria and the rapid spread of resistance genes. These resistance genes are spreading among bacterial species with various mobile genetic elements such as plasmids, transposons and integrons. Integrons are known genetic elements that encode many antibiotic resistance determinants and have the ability to carry or integrate specific gene cassettes. In this study, identification of the presence of integron gene cassette and its resistance patterns in 112 E. coli isolates isolated from blood cultures sent to Farabi Hospital Medical Microbiology Training and Service Laboratory of Karadeniz Technical University between January and December 2014, and determination of the resistance patterns of the conjugative plasmids involved in the transfer of integrons, and the incompatibility (Inc) groups of these plasmids were grouped by replicon typing method. Polymerase chain reaction (PCR) was performed by using intI1 gene specific primers to identify the integron gene region of the class 1 integron in the 112 E. coli isolates. Based on PCR results, in 51 (45.5%) of the 112 E. coli isolates were detected positive for intI1. For the identification of the integrase gene region of the class 2 integron, in 7 of the 112 E. coli isolates (6.3%) were identified as intI2 positive using intI2 gene specific primers. It was determined that 13 isolates contained empty integrons while class 1 integron presence was detected in 38 (33.9%) of the 112 isolates resulting from the PCR reaction to determine the presence of class 1 and class 2 integron. In 7 (6.3%) of 112 isolates class 2 integrons were present. Sequence analysis of 38 isolates with class 1 integron revealed 5 types of gene cassettes called dfrA7, dfr17-aadA5, dfrV, dfrA1-aadA1 and dfrA12-aadA2, which are responsible for resistance to trimethoprim and streptomycin-spectinomycin resistance. Sequence analysis of 7 isolates found to be positive for class 2 integron amplification revealed two types of gene cassettes identified as dfrA1-sat2-aadA1 and dfrA1-sat2-aadA30. Sequence analysis results of 14 isolates could not be obtained. Conjugation experiment was performed based on the principle of broth mating method. Of the 45 E. coli having class 1 and class 2 integron tested, 35 (78%) of them were found to be conjugated to the recipient cell (E. coli J53-2 met pro RifR) and conjugation efficiency was ranged from 10-6 to 10-10. PCR amplification for the identification of Inc groups in the 35 transconjugant containing conjugated plasmid resulted in IncN in 6 (17%) isolates, IncQ in 1 (3%) isolates. And no isolates were found in IncP and IncW.