Emergence of a novel multidrug-resistant Pseudomonas aeruginosa strain producing IMP-type metallo-β-lactamases and AAC(6')-Iae in Japan.

The emergence of multidrug-resistant (MDR) Pseudomonas aeruginosa isolates producing IMP-type metallo-β-lactamases (MBLs) and aminoglycoside 6'-N-acetyltransferase [AAC(6')-Iae] has become a serious problem in medical settings in Japan. A total of 217 MDR P. aeruginosa isolates were obtained from August 2009 to April 2010 from patients at 144 hospitals in Japan, of which 145 (66.8%) were positive for IMP-type MBLs and AAC(6')-Iae when tested with an immunochromatographic assay. Polymerase chain reaction (PCR) showed that these isolates were also positive for blaIMP and aac(6')-Iae genes. When these IMP-type MBL- and AAC(6')-Iae-producing isolates were analysed by pulsed-field gel electrophoresis (PFGE), two clusters (I and II) were detected. Most of the isolates (88.3%; 128/145) were grouped under cluster I and had multilocus sequence type ST235 and serotype O11, except for one isolate that was ST991 and serotype O3. The isolates were mainly isolated from the urinary tract (82/145; 56.6%) and respiratory tract (58/145; 40.0%). The epidemiological properties of the isolates belonging to cluster I were similar to those of MDR P. aeruginosa isolates that have been previously reported in Japan. The remaining 16 isolates belonged to cluster II, had identical PFGE patterns and were multilocus sequence type ST991 and serotype O18; all of these isolates were isolated from the respiratory tract. The properties of isolates belonging to cluster II have not been previously described, indicating that a novel IMP-type MBL- and AAC(6')-Iae producing P. aeruginosa strain is emerging in Japan. Isolates belonging to both clusters were isolated from different parts of the country.