Prevalence and diversity of integrons and associated resistance genes in faecal Escherichia coli isolates of healthy humans in Spain.

OBJECTIVES: To analyse the prevalence and diversity of integrons in faecal Escherichia coli isolates from healthy humans in Spain.

METHODS: One hundred E. coli isolates were obtained in Levine agar plates from faecal samples of 100 healthy humans during March to October 2007. Susceptibility to 16 antimicrobial agents was determined by the disc diffusion method. The presence and characterization of class 1, 2 and 3 integrons, as well as the presence of other antimicrobial resistance genes, were performed by PCR and DNA sequencing.

RESULTS: Integrases associated with class 1 and/or class 2 integrons were identified in 29 E. coli isolates (intI1 gene in 26 isolates, intI2 in 1 isolate and intI1 + intI2 in 2 isolates), the remaining 71 isolates being free of these integrons. Seven different gene cassette arrangements were demonstrated in 27 of the 28 intI1-positive isolates and were as follows (number of isolates): dfrA1 + aadA1 (12), aadA (8), dfrA17 + aadA5 (3), dfrA7 (1), dfrA5 (1), dfrA1 (1) and dfrA12 + orfF + aadA2 (1). Four isolates presented defective class 1 integrons lacking the 3'-conserved region. The three isolates containing class 2 integrons harboured the dfrA1 + sat + aadA1 gene cassette array in their variable region. Integron-positive isolates showed higher percentages of resistance to streptomycin, ampicillin, tetracycline, trimethoprim, sulfamethoxazole, chloramphenicol and nalidixic acid than integron-negative isolates. Sixty-five percent of the integron-positive isolates belonged to phylogenetic groups A or D.

CONCLUSIONS: A high prevalence of integrons was detected in faecal E. coli of healthy humans. Individuals in the community could be a reservoir of integron-containing E. coli isolates.