Molecular diversity of class 1 integrons in human isolates of Aeromonas spp. from southern Taiwan.

This work studies antimicrobial resistance and class 1 integrons of Aeromonas spp. in human isolates from southern Taiwan. PCR amplification and DNA sequence analyses were performed to characterize the gene cassette regions of the class 1 integron in 204 isolates of Aeromonas hydrophila, 36 isolates of A. sobria, 23 isolates of A. veronii, and 4 isolates of A. caviae. By using Southern hybridization with an intI1 probe to determine the presence of class 1 integrons in the 9 isolates of Aeromonas spp. harboring plasmid DNA, only 2 isolates, one A. veronii AV69 harboring 176-kb plasmid DNA, and one A. hydrophila AH207 harboring 149-kb plasmid DNA were identified. A conjugation experiment was carried out with 2 isolates of A. veronii AV69 and A. hydrophila AH207. Only one transconjugant of Escherichia coli AH207, containing 149-kb plasmids obtained from A. hydrophila AH207, was identified. ERIC-PCR analysis was performed to analyze the genetic relatedness in all isolates of Aeromonas spp. that carry class 1 integrons. The results of cluster analysis in this experiment revealed that none of these isolates were clonal, which may indicate that they were not related to the outbreak. Among the 267 isolates tested, class 1 integrons were detected in 37 isolates (13.9%) of Aeromonas spp. from humans. No class 2 or class 3 integrons were detected in this study. Gene cassette structures were identified in 30 (81.0%) of 37 isolates of Aeromonas spp. containing class 1 integrons. The gene cassette of dfrA12-orfF-aadA2 was the most prevalent in the gene cassette array (16.0%), followed by arr3-aacA4 (13.3%) and dfr2d-catB3-aadA1 (10.0%). Four novel arrays of gene cassettes were also identified, namely, dfr2d-catB3-aadA1, aadA1-aac(6')-II, aadA4a, and aac(6')-II-blaOXA-21-catB3. This is the first report of Aeromonas spp. isolates from humans.