Increase of metallo-beta-lactamase producing bacteria positive cases including Klebsiella pneumoniae in a Japanese university hospital]

The clinical characteristics of the metallo-beta-lactamase (MBL) producing bacteria were investigated in a Japanese university hospital with 661 beds. In total, 34 cases (38 strains) were isolated from March 2006 to October 2007. No MBL-producing strain was detected until then. We screened for MBL using Arakawa's method because it detects MBL-producing bacteria more sensitively than conventional methods. Anti-biotic resistant genes were analyzed in 24 MBL producing bacteria positive cases detected from September 2007 to August 2008. Either bla(IMP-1) or bla(IMP-11) was detected in all cases. Age distribution of the MBL producing bacteria positive cases had two peaks, infant age (under five-years-old) and senior age (over seventies). All cases have underlying diseases, such as diabetes mellitus, malignant tumor, granulocytopenia, and/or using steroids. Twenty-one strains were detected from postoperative cases. MBL carrier rate in total clinically isolated Klebsiella pneumoniae strains was 2.6%. As far as we know, this number is the highest among reports in Japanese hospitals. The clinical manifestation of K. pneumoniae as pathogen was identified in only two cases (5%). In 24 cases (82%), MBL-producing bacteria were identified as bystanders. Though infection cases by MBL-producing bacteria especially by K. pneumoniae have not been frequently observed, we should carefully watch their numbers because the bacteria transfer resistant genes among their flora.