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Antimicrobial Agents and Chemotherapy, February 2005, p. 600-605, Vol. 49, No. 2
0066-4804/05/$08.00+0     doi:10.1128/AAC.49.2.600-605.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Novel SHV-Derived Extended-Spectrum ß-Lactamase, SHV-57, That Confers Resistance to Ceftazidime but Not Cefazolin

Ling Ma,¹ Jimena Alba,² Feng-Yee Chang,³ Masaji Ishiguro,⁴ Keizo Yamaguchi,² L. K. Siu,^1* and Yoshikazu Ishii²

Division of Clinical Research, National Health Research Institutes,¹ Division of Infectious Disease and Tropical Medicine, Department of Internal Medicine, Tri-Service General Hospital, National Defense Medical Center, Taipei, Taiwan,³ Department of Microbiology, Toho University School of Medicine, Tokyo,² Suntory Institute for Bioorganic Research, Shimamoto, Osaka, Japan⁴

Received 14 April 2004/ Returned for modification 19 June 2004/ Accepted 3 October 2004

A new SHV-derived extended-spectrum ß-lactamase, SHV-57, that confers high-level resistance to ceftazidime but not cefotaxime or cefazolin was identified from a national surveillance study conducted in Taiwan in 1998. An Escherichia coli isolate resistant to ampicillin, cephalothin, and ceftazidime but sensitive to cefoxitin, ceftriaxone, cefotaxime, imipenem, and a narrow-spectrum cephem (cefazolin) was isolated from the urine of a patient treated with ß-lactam antibiotics. Resistance to ß-lactams was conjugatively transferred with a plasmid of about 50 kbp. The pI of this enzyme was 8.3. The sequence of the gene was determined, and the open reading frame of the gene was found to consist of 861 bases (GenBank accession number AY223863). Kinetic parameters showed that SHV-57 had a poor affinity to cefazolin. The K_m value toward cefazolin (5.57 x 10³ µM) was extremely high in comparison to those toward ceftazidime (30.9 µM) and penicillin G (67 µM), indicating its low affinity to cefazolin. Although the K_m value of the ß-lactamase inhibitor was too high for the study of catalytic activity (k_cat), indicating the low k_cat of SHV-57, the SHV-57 carrier was highly susceptible to a ß-lactam-ß-lactamase inhibitor combination. Comparison of the three-dimensional molecular model of SHV-57 with that of the SHV-1 ß-lactamase suggests that the substitution of arginine for leucine-169 in the loop is important for the substrate specificity.

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* Corresponding author. Mailing address: Division of Clinical Research, National Health Research Institutes (99), 128, Yen-Chiu-Yuan Rd., Sec. 2., Taipei, 11529, Taiwan. Phone: 886 2 26524094. Fax: 886 2 27890254. E-mail: lksiu{at}nhri.org.tw.

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Antimicrobial Agents and Chemotherapy, February 2005, p. 600-605, Vol. 49, No. 2
0066-4804/05/$08.00+0     doi:10.1128/AAC.49.2.600-605.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

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