Structural Diversity of Class 1 Integrons in Multiresistant Strains of Escherichia coli Isolated from Patients in a Hospital in Mexico City.

Since a decade, Escherichia coli has been considered an important nosocomial pathogen due to the high number of isolates multiresistant to antimicrobials reported worldwide. In clinical and environmental strains, transposons, plasmids, and integrons are currently considered the principal genetic elements responsible for the acquisition of antibiotic resistance through horizontal transfer. The objective of this research was to correlate the resistance to antibiotics of E. coli clinical strains with the presence class I integrons. In the present study, one hundred E. coli strains were isolated and tested for susceptibility and resistance to antimicrobials. Class 1 integrons were detected by PCR, and the arrangement of gene cassettes was determined by sequencing. Twenty two strains were found to carry Class 1 integrons. Sequence analysis of the variable regions revealed the presence of several gene cassettes, such as dihydrofolate reductases (dfr2d, dfrA17, and dhfrXVb), adenylyl transferases (aadA2, addA5, and addA22), and chloramphenicol efflux pump (cmlA), and oxacillinase (bla OXA-1 ). The dfrA17-addA5 arrangement prevailed upon other integrons in the study. This is the first report of the presence of the dfr2d and dhfrXVb-aadA2 cassette arrangements in a Class 1 integrons from clinical strains of E. coli. In most of the strains, it was found a direct relationship between genetic arrangements and resistance phenotypes. Four integrons were detected in plasmids that might be involved in the resistance genes transfer to other bacteria of clinical importance. Our results confirm the presence of Class 1 integrons and their essential role in the dissemination of resistance cassettes among E. coli strains.