Dissemination of bla(IMP-1)-carrying integron In86 among Klebsiella pneumoniae isolates harboring a new trimethoprim resistance gene dfr23.

The genetic context of the bla(IMP-1) gene was evaluated in 9 Klebsiella pneumoniae isolates recovered from 2 hospitals in São Paulo, Brazil. All isolates harbored a copy of In86 carrying bla(IMP-1), aac(6')-31, and aadA1. Eight strains from the same hospital also carried another class 1 integron harboring a new trimethoprim resistance gene (dfr23) that was chromosomally embedded. In86 was likely to be in a 30-kb nontransferable plasmid and was flanked upstream by a sequence identical to one identified in an IMP-1-producing Pseudomonas putida isolate. The bla(IMP-1)-carrying integron In86 was recently reported from nonfermentative bacilli isolated in São Paulo. These isolates appear to be the source of this integron now acquired by K. pneumoniae strains from different hospitals in the same city. Metallo-beta-lactamase production is still rare among Enterobacteriaceae isolates in Brazil, but the acquisition of genetic structures carrying these mobile resistance determinants is worrisome and could lead to an increase in the prevalence of these phenotypes of resistance.