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Antimicrobial Agents and Chemotherapy, April 2006, p. 1610-1611, Vol. 50, No. 4
0066-4804/06/$08.00+0     doi:10.1128/AAC.50.4.1610-1611.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

LETTER TO THE EDITOR

First Isolation of blaIMI-2 in an Enterobacter cloacae Clinical Isolate from China


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Carbapenem resistance mediated by acquired carbapenemases is a growing concern worldwide. Acquired class A carbapenemases of the NMC/IMI, SME, and KPC types remain infrequent in Enterobacteriaceae (2, 6-8), but some of them have increasingly been reported recently (10). IMI-1 was first described in 1996 in clinical isolates of Enterobacter cloacae (9). Recently, IMI-2, a variant that differs from IMI-1 by 2 amino acid residues, was found in a strain of Enterobacter asburiae isolates in U.S. rivers (1). In this study, we report on the detection of IMI-2 in a clinical isolate of Enterobacter cloacae from China.

An imipenem-resistant E. cloacae isolate (isolate 8) was obtained from the blood of a patient in our hospital in August 2001. The patient had previously been treated with ampicillin-sulbactam and cefotaxime. E. cloacae isolate 8 was resistant to imipenem, meropenem, and ertapenem; had intermediate resistance to cefotaxime and ceftazidime; and was susceptible to cefepime (Table 1). Conjugation was carried out by a broth method as previously described (11). Transconjugant clones were selected on Mueller-Hinton agar containing rifampin (256 mg/liter) and imipenem (4 mg/liter). Imipenem resistance was transferred to a transconjugant along with a plasmid with a size of about 80 kb. The MIC for the transconjugant (Escherichia coli C600E8) showed that it has resistance to carbapenems but not to expanded-spectrum cephalosporins (Table 1). The ß-lactamase activity was determined by UV spectrophotometry with imipenem as a substrate (1, 5). In E. coli C600E8, expression of carbapenemase activity increased from 643 to 1,352 U/mg of protein upon exposure to imipenem (4 mg/liter) as an inducer. These results demonstrated that the ß-lactamase was produced at a high basal level and that expression was very poorly inducible. Isoelectric focusing was performed according to a published protocol (3). The result demonstrated that E. cloacae 8 had 5 pI bands at pI 5.1, 5.4, 6.9, 8.1, and 8.6, while E. coli C600E8 had only one band at pI 8.1, which was inhibited by clavulanic acid.


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  		TABLE 1. MICs of selected antimicrobial agents for various strains determined by Etest

 
The imipenem resistance gene was cloned into pGEM-T Easy (Promega, Madison, Wis.) as a 10.6-kb EcoRI fragment. A 10,629-bp stretch of DNA sequence was obtained by nucleotide sequencing on both strands (GenBank accession no. AY780889). In the cloned fragment, blaIMI-2 is preceded by a gene encoding a protein 97% identical to ImiR (9). The regions flanking the blaIMI-R2-blaIMI-2 gene contain sequences related to Tn903 (4) and IS2 (Fig. 1). Their structure apparently differs from that previously reported to be flanking the blaIMI-R2-blaIMI-2 gene complex from E. asburiae (1). The transposable elements flanking the blaIMI-R2-blaIMI-2 gene complex could be involved in mobilization of the carbapenemase gene to enterobacterial plasmids.


Figure 1
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  		FIG. 1. Schematic representation of the structure of the region containing the blaIMI-R2-blaIMI-2 gene complex from the E. cloacae 8 plasmid. The two sides of the blaIMI-R2-blaIMI-2 gene are inverted repeat sequences. "Tn903-like" downstream is an incomplete open reading frame that is part of "Tn903-like" upstream.

 


   ACKNOWLEDGMENTS
 
This work was supported in part by the National Basic Research Program 973 of China (no. 2005CB523101) and the Program for New Century Excellent Talents in University (no. NCET-04-0552).


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  1. Aubron, C., L. Poirel, R. J. Ash, and P. Nordmann. 2005. Carbapenemase-producing Enterobacteriaceae, U.S. rivers. Emerg. Infect. Dis. 11:260-264.[Medline]
  2. Bush, K., G. A. Jacoby, and A. A. Medeiros. 1995. A functional classification scheme for ß-lactamases and its correlation with molecular structure. Antimicrob. Agents Chemother. 39:1211-1233.[Medline]
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  4. Grindley, N. D., and C. M. Joyce. 1980. Genetic and DNA sequence analysis of the kanamycin resistance transposon Tn903. Proc. Natl. Acad. Sci. USA 77:7176-7180.[Abstract/Free Full Text]
  5. Laurent, P., T. Naas, M. Guibert, E. B. Chaibi, R. Labia, and P. Nordmann. 1999. Molecular and biochemical characterization of VEB-1, a novel class A extended-spectrum ß-lactamase encoded by an Escherichia coli integron gene. Antimicrob. Agents Chemother. 43:573-581.[Abstract/Free Full Text]
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  7. Nordmann, P., and L. Poirel. 2002. Emerging carbapenemases in Gram-negative aerobes. Clin. Microbiol. Infect. 8:321-331.[CrossRef][Medline]
  8. Nordmann, P., and L. Poirel. 2002. Acquired carbapenem-hydrolyzing ß-lactamases and their genetic support. Curr. Pharm. Biotechnol. 3:117-127.[CrossRef][Medline]
  9. Rasmussen, B. A., K. Bush, D. Keeney, Y. Yang, R. Hare, C. O'Gara, and A. A. Medeiros. 1996. Characterization of IMI-1 ß-lactamase, a class A carbapenem-hydrolyzing enzyme from Enterobacter cloacae. Antimicrob. Agents Chemother. 40:2080-2086.[Abstract]
  10. Woodford, N., P. M. Tierno, Jr., K. Young, L. Tysall, M.-F. I. Palepou, E. Ward, R. E. Painter, D. F. Suber, D. Shungu, L. L. Silver, K. Inglima, J. Kornblum, and D. M. Livermore. 2004. Outbreak of Klebsiella pneumoniae producing a new carbapenem-hydrolyzing class A ß-lactamase, KPC-3, in a New York medical center. Antimicrob. Agents Chemother. 48:4793-4799.[Abstract/Free Full Text]
  11. Yan, J.-J., W. C. Ko, and J.-J. Wu. 2001. Identification of a plasmid encoding SHV-12, TEM-1, and a variant of IMP-2 metallo-ß-lactamase, IMP-8, from a clinical isolate of Klebsiella pneumoniae. Antimicrob. Agents Chemother. 45:2368-2371.[Abstract/Free Full Text]
Yun-Song Yu*
Xiao-Xing Du
Zhi-Hui Zhou
Ya-Gang Chen
Lan-Juan Li
The Key Lab of Infectious Diseases of
 Public Health Ministry
The 1st Affiliated Hospital
Medical School
Zhejiang University
Zhejiang
Hangzhou, China

* Phone: 86 571 8723 6756, Fax: 86 571 8723 6994, E-mail: yvys119{at}163.com

Antimicrobial Agents and Chemotherapy, April 2006, p. 1610-1611, Vol. 50, No. 4
0066-4804/06/$08.00+0     doi:10.1128/AAC.50.4.1610-1611.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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