Interspecies dissemination of a novel class 1 integron carrying blaIMP-19 among Acinetobacter species in Japan

Abstract

Objectives: To analyse the dissemination of metallo-β-lactamase genes and mobile genetic elements among Acinetobacter spp.

Methods: From January 2004 to December 2010, 16 Acinetobacter isolates that were positive for metallo-β-lactamase production were collected and analysed. Antimicrobial susceptibilities were studied, and molecular typing was performed using PFGE and multilocus sequence typing (MLST). The resistance genes, including carbapenemase-encoding genes and aminoglycoside resistance genes, were detected by PCR. Mobile genetic elements were identified by nucleotide sequence analysis and PCR mapping of the integron gene cassettes and the insertion sequence (IS) elements.

Results: We identified 10 Acinetobacter genospecies 3 isolates that belonged to three PFGE clusters and four MLST types, 4 Acinetobacter johnsonii isolates that belonged to the same PFGE cluster, 1 Acinetobacter baumannii isolate and 1 Acinetobacter junii isolate. Each isolate was not susceptible to at least one carbapenem. The bla(IMP-19) gene was found in two PFGE clusters of genospecies 3, in the one PFGE cluster of A. johnsonii and in each of the A. baumannii and A. junii isolates, and was located in a class 1 integron as a gene cassette array of bla(IMP-19)-aac(6')-31-bla(OXA-21)-aadA1. One genospecies 3 isolate harboured bla(IMP-11), bla(OXA-58). This isolate harboured three mobile elements, including a class 1 integron that carried bla(IMP-11), another class 1 integron that carried catB8-like/aacA4-aadA5 and an IS element (bla(OXA-58) flanked an either side by ISAba3).

Conclusions: We demonstrated that the bla(IMP-19) gene carried in the novel class 1 integron gene cassette array of bla(IMP-19)-aac(6')-31-bla(OXA-21)-aadA1 has been horizontally disseminated among different Acinetobacter spp. Additionally, one isolate harboured multiple mobile genetic elements.