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Journal of Antimicrobial Chemotherapy

Year: 2009  |  Volume: 64  |  Issue: 1  |  Page No.: 46 - 51

Increased prevalence and clonal dissemination of multidrug-resistant Pseudomonas aeruginosa with the blaIMP-1 gene cassette in Hiroshima

S Kouda, M Ohara, M Onodera, Y Fujiue, M Sasaki, T Kohara, S Kashiyama, S Hayashida, T Harino, T Tsuji, H Itaha, N Gotoh, A Matsubara, T Usui and M. Sugai

Abstract

Objectives

The aim of this study was to evaluate the dissemination of metallo-β-lactamase (MBL)-encoding genes among multidrug-resistant (MDR) Pseudomonas aeruginosa isolates recovered from major hospitals in the Hiroshima region.

Methods

During July to December from 2004 to 2006, a surveillance of eight major hospitals in the Hiroshima region identified 387 non-duplicate isolates resistant to imipenem (MIC ≥ 16 mg/L). They were screened for resistance to amikacin (MIC ≥ 64 mg/L) and ciprofloxacin (MIC ≥ 4 mg/L) and MBL-encoding genes. The structure of the variable regions of the integrons was determined using PCR mapping. Clonality was assessed using PFGE and multilocus sequence typing (MLST).

Results

The frequency of MBL-positive isolates in MDR P. aeruginosa isolates significantly increased from 42.3% in 2004 to 81.4% in 2006. Most of the MBL-positive isolates produced IMP-1 followed by VIM-2. The blaIMP-1 and blaVIM-2 genes were present in class 1 integrons. Characterization of the variable regions of the integron showed the presence of six different gene cassette arrays in blaIMP-1 cassettes and a single array in blaVIM-2 cassettes. The IMP-1 producers belonged to two clonal lineages using PFGE and MLST analyses and the integron variations correlated well with the clonal complexes. Among them, strains positive for a newly identified In113-derived blaIMP-1 gene cassette array were most widely distributed in Hiroshima.

Conclusions

This study shows a dramatic increase in MBL genes, primarily blaIMP-1, in MDR P. aeruginosa isolates in Hiroshima during these 3 years. In addition, MDR P. aeruginosa with the newly discovered In113-derived blaIMP-1 gene cassette array appears to be clonally expanding.

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