Molecular epidemiology of orf513-bearing class 1 integrons in multiresistant clinical isolates from Argentinean hospitals

Abstract

The spread of orf513-bearing class 1 integrons is associated with bla(CTX-M-2) in gram-negative clinical isolates in Argentina, with In35 being the most frequently found integron (74%). Among 65 isolates without bla(CTX-M-2), only one harbored a novel orf513-bearing class 1 integron with the dfrA3b gene. The finding of orf513 not associated with class 1 integrons in two gram-positive strains indicates the widespread occurrence of this putative site-specific recombinase.

FIG. 1.

(A) Structure of In35 containing the bla_CTX-M-2 gene. Orf3::QacEΔ1 is a fusion protein (GenPept AAM03346). (B) Percentages of the different arrangements of cassettes characterized in the variable regions (solid bars) of the unusual class 1 integrons harboring bla_CTX-M-2.

FIG. 2.

Characterization of the genetic structure of In38 from an isolate of Citrobacter freundii. (A) Region characterized by PCR mapping. (B) Lengths of the PCR products obtained with different combinations of primers listed in Table 2.(C) Representation of sequence reported in this study (GenBank accession number AY162283) relative to structures depicted in panels A and B.

FIG. 3.

Deletionsat the 5′ ends of the second 3′-CSs in In35 (bla_CTX-M-2), In7 (dfrA10), In6 (catII), and In38 (dfrA3b). Base 1 corresponds to the first base of a typical 3′-CS. Nucleotides that differ from those in a typical 3′-CS are shown in bold.