JAC Advance Access originally published online on April 27, 2009
Journal of Antimicrobial Chemotherapy 2009 64(1):46-51; doi:10.1093/jac/dkp142
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Original research |
Increased prevalence and clonal dissemination of multidrug-resistant Pseudomonas aeruginosa with the blaIMP-1 gene cassette in Hiroshima
1 Department of Bacteriology, Hiroshima University Graduate School of Biomedical Sciences, Hiroshima, Japan 2 Department of Urology, Hiroshima University Graduate School of Biomedical Sciences, Hiroshima, Japan 3 Clinical Laboratory, Hiroshima University Hospital, Hiroshima, Japan 4 Department of Pathology and Clinical Laboratory Medicine, Hiroshima Prefecture Hospital, Hiroshima, Japan 5 Clinical Laboratory, Hiroshima City Hospital, Hiroshima, Japan 6 Clinical Laboratory, Hiroshima Red Cross Hospital and Atomic-bomb Survivors Hospital, Hiroshima, Japan 7 Clinical Laboratory, Hiroshima Saiseikai Hospital, Hiroshima, Japan 8 Clinical Laboratory, Hiroshima General Hospital, Hiroshima, Japan 9 Clinical Laboratory, Hiroshima City Asa Hospital, Hiroshima, Japan 10 Clinical Laboratory, Shobara Red Cross Hospital, Hiroshima, Japan 11 Department of Microbiology and Infection Control Science, Kyoto Pharmaceutical University, Kyoto, Japan
Received 6 January 2009; returned 18 January 2009; revised 9 March 2009; accepted 26 March 2009
* Corresponding author. Tel: +81-82-257-5636; Fax: +81-82-257-5639; E-mail: Sugai{at}hiroshima-u.ac.jp
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.
Keywords: metallo-β-lactamases , integrons , epidemiology