Escherichia coli strain TUM2139 was isolated from a stool sample from a 9-year-old girl on 16 June 2004. This strain was categorized as Shiga toxin-producing Escherichia coli (STEC) because the Shiga-like toxin gene stx 1 was detected by immunochromatography and PCR assay. The strain was highly resistant to cefotaxime (256 g/ml) and was also resistant to cefepime, cefpodoxime, ceftriaxone, and aztreonam. In the presence of 4 g of clavulanic acid per ml, the MIC of cefotaxime decreased to <0.12 g/ml, indicating that this strain was an extended-spectrum ␤-lactamase (ESBL) producer. Cefotaxime resistance was transferred to E. coli C600 by conjugation at a frequency of 3.0 ؋ 10 ؊6 . A PCR assay was performed with primer sets specific for TEM-type and SHV-type ESBLs and for the CTX-M-2 (Toho-1), CTX-M-3, and CTX-M-9 groups of ESBLs. A specific signal was observed with the primer set specific for the CTX-M-9 group of ␤-lactamases. This ␤-lactamase was confirmed to be the ESBL CTX-M-18 by DNA sequencing. This is the first report of an ESBL-producing STEC isolate.

The aim of this study was to determine the distribution of metallo-␤-lactamase-producing Pseudomonas aeruginosa in Japan and to investigate the molecular characteristics of resistance gene cassettes including the gene encoding this enzyme. A total of 594 nonduplicate strains of P. aeruginosa isolated from 60 hospitals throughout Japan in 2002 were evaluated. This study indicated that although the prevalence of imipenemresistant P. aeruginosa has not increased compared to that found in previous studies, clonal distribution of the same strain across Japan is evident.Class A, B, and D ␤-lactamases, as defined by Ambler et al., can hydrolyze carbapenems (1, 9). In particular, class B ␤-lactamases, termed metallo-␤-lactamases, are an increasingly serious clinical problem because they have a very broad substrate profile that includes penicillins, expanded-spectrum cephalosporins, and carbapenems and excludes only monobactams, such as aztreonam. It has been reported that IMP-1 metallo-␤-lactamase-producing Serratia marcescens was first isolated in Japan in 1991 (10). Recently, metallo-␤-lactamase-producing Pseudomonas aeruginosa and S. marcescens probably have the highest incidence of isolation in Japan (7).Most metallo-␤-lactamase genes are located on integrons, which are genetic elements containing gene cassettes that can facilitate their spread and mobilize the genes to other integrons or to other sites. The gene cassettes often encode clinically important antibiotic resistance genes, including those encoding ␤-lactamases such as extended-spectrum ␤-lactamases and carbapenemases, and also aminoglycoside-modifying enzymes (12).Little is known about the distribution of the clone(s) that produces metallo-␤-lactamases in Japan. Therefore, we conducted a surveillance study covering a wide geographic area with the aim of determining the distribution of metallo-␤-lactamase producers in Japan and to investigate the molecular characteristics of the resistance gene cassettes that included the gene encoding a metallo-␤-lactamase.A total of 594 nonduplicate strains of P. aeruginosa isolated from 60 hospitals throughout Japan in the year 2002 were evaluated. The susceptibility of P. aeruginosa to several antibiotics was measured with the Etest strip, and the strains were stored on Casitone medium (Eiken Chemical Co. Ltd., Tokyo, Japan) (data not shown). After 6 months, the antibiotic susceptibility of these isolates was reassessed by the National Committee for Clinical Laboratory Standards broth microdilution method with cation-adjusted Mueller-Hinton broth (Difco, Detroit, Mich.). The isolates were screened for the presence of metallo-␤-lactamase by a double-disk synergy test reported by Arakawa et al. (2). Integron analysis was performed by PCR mapping (5Ј-conserved segment intI to 3Ј-conserved segment qacE⌬1) of the typical antibiotic resistance genes and integron with specific primer sets ( Table 1). The specificity of the primer sets for bla IMP-1 -like and bla VIM-2 -like gene was confirmed with positive-control strains pr...

In 2002, 495 indole-positive proteae strains were isolated from patients at 60 hospitals in Japan. Nine indole-positive proteae strains had reduced susceptibility to imipenem (MIC > 8 ìg ml À1 ) and were identified as Providencia rettgeri by BD Phoenix. Eight of the nine Prov. rettgeri isolates were confirmed as metallo-â-lactamase producers by the double-disc synergy test. All the metallo-â-lactamases were classified as IMP-1 by PCR and DNA sequence analysis. These bla IMP-1 genes were encoded in the integron structure on conjugative plasmids. These plasmids could transfer from Prov. rettgeri clinical isolates to Escherichia coli ML4903 at a frequency between 1 . 5 3 10 À5 and 5 . 5 3 10 À7 . The eight bla IMP -positive strains were isolated from two hospitals, and showed two different PFGE patterns, two different integron structures and two different incompatibility groups, which corresponded to the two hospitals. These results strongly suggest the possibility of nosocomial infections by bla IMP-1 -producing Prov. rettgeri isolates.