Molecular characterization of integrons in Acinetobacter baumannii: description of a hybrid class 2 integron

Abstract

Twenty Acinetobacter baumannii strains resistant to various antibiotics were analyzed for integron content and sequences of the amplification products. Sixteen clinical isolates had a class 1 integron, 2 contained an additional class 1 or class 2 integron, but no class 3 integron was detected. Thirteen strains had integrons with a single cassette: aac(3)-Ia (9 strains), ant(2")-Ia (2 strains), or aac(6')-Ib (2 strains); 1 had aac(6')-Ib and oxa20 cassettes and an unknown gene; and 1 had an integron containing ant(2")-Ia and an oxa3 cassette truncated by IS6100. The remaining strains harbored class 1 integrons with gene cassettes previously found in Enterobacteriaceae. One integron had a hybrid structure composed of intI2 and the 3' conserved segment of class 1 integrons. These data indicate that integrons play a major role in multidrug resistance in Acinetobacter.

FIG. 1

Physical maps of the class 1 integron of BM4430 (A) and of the hybrid integron of BM4431 (B). Filled circle, attC site; open arrows, coding sequences; arrowheads, primers.