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Antimicrobial Agents and Chemotherapy, August 2000, p. 2023-2027, Vol. 44, No. 8
0066-4804/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Amino Acid Substitutions in a Variant of IMP-1 Metallo-beta -Lactamase

Shizuko Iyobe,1,* Haruko Kusadokoro,2 Junko Ozaki,2 Naoki Matsumura,3 Shinzaburo Minami,3 Shin Haruta,2 Tetsuo Sawai,2 and Koji O'Hara2

Laboratory of Drug Resistance in Bacteria, Gunma University School of Medicine, Maebashi,1 Division of Microbial Chemistry, Faculty of Pharmaceutical Sciences, Chiba University, Chiba,2 and Research Laboratory, Toyama Chemical Co., Ltd., Toyama,3 Japan

Received 8 October 1999/Returned for modification 31 January 2000/Accepted 5 May 2000

In the course of surveying for the carbapenem-hydrolyzing metallo-beta -lactamase gene blaIMP in pathogenic bacteria by the PCR method, we detected a gene encoding a variant metallo-beta -lactamase, designated IMP-3, which differed from IMP-1 by having low hydrolyzing activity for penicillins and carbapenems. PCR product direct sequencing of a 2.2-kb segment revealed that the gene blaIMP-3 was located on a cassette inserted within a class I integron in the pMS390 plasmid. The 741-bp nucleotide sequence of blaIMP-3 was identical to that of blaIMP-1, except for seven base substitutions. Among these were two, at nucleotide positions 314 and 640, which caused amino acid alterations. Hybrid bla genes were constructed from blaIMP-3 and blaIMP-1 by recombinant DNA techniques, and beta -lactamases encoded by these genes were compared with those of the parents IMP-3 and IMP-1 under the same experimental conditions. The kinetic parameters indicated that the inefficient hydrolysis of benzylpenicillin, ampicillin, imipenem, and ceftazidime by IMP-3 was due to the substitution of glycine for serine at amino acid residue 196 in the mature enzyme. This alteration corresponded to the presence of guanine instead of an adenine at nucleotide position 640 of the blaIMP-3 gene. This indicated that extension of the substrate profile in the metallo-beta -lactamase IMP-1 compared to IMP-3 is the result of a one-step single-base mutation, suggesting that the gene blaIMP-3 is an ancestor of blaIMP-1.

* Corresponding author. Mailing address: Laboratory of Drug Resistance in Bacteria, Gunma University School of Medicine, 3-39-22, Showa-Machi, Maebashi, 371-8511, Japan. Phone: 81-27-220-8087. Fax: 81-27-220-8088. E-mail: siyobe{at}akagi.sb.gunma-u.ac.jp.

Antimicrobial Agents and Chemotherapy, August 2000, p. 2023-2027, Vol. 44, No. 8
0066-4804/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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