Plasmid-encoded metallo-beta-lactamase (IMP-6) conferring resistance to carbapenems, especially meropenem.
In 1996, Serratia marcescens KU3838 was isolated from the urine of a patient with a urinary tract infection at a hospital in northern Japan and was found to contain the plasmid pKU501. Previously, we determined that pKU501 carries bla(IMP) and the genes for TEM-1-type beta-lactamases as well as producing both types of beta-lactamases (H. Yano, A. Kuga, K. Irinoda, R. Okamoto, T. Kobayashi, and M. Inoue, J. Antibiot. 52:1135-1139, 1999). pKU502 is a recombinant plasmid that contains a 1.5-kb DNA fragment, including the metallo-beta-lactamase gene, and is obtained by PCR amplification of pKU501. The sequence of the metallo-beta-lactamase gene in pKU502 was determined and revealed that this metallo-beta-lactamase gene differed from the gene encoding IMP-1 by one point mutation, leading to one amino acid substitution: 640-A in the base sequence of the IMP-1 gene was replaced by G, and Ser-196 was replaced by Gly in the mature enzyme. This enzyme was designated IMP-6. The strains that produced IMP-6 were resistant to carbapenems. The MICs of panipenem and especially meropenem were higher than the MIC of imipenem for these strains. The k(cat)/K(m) value of IMP-6 was about sevenfold higher against meropenem than against imipenem, although the MIC of meropenem for KU1917, which produced IMP-1, was lower than that of imipenem, and the MIC of panipenem was equal to that of imipenem. These results support the hypothesis that IMP-6 has extended substrate profiles against carbapenems. However, the activity of IMP-6 was very low against penicillin G and piperacillin. These results suggest that IMP-6 acquired high activity against carbapenems, especially meropenem, via the point mutation but in the process lost activity against penicillins. Although IMP-6 has reduced activity against penicillins due to this point mutation, pKU501 confers resistance to a variety of antimicrobial agents because it also produces TEM-1-type enzyme.
Yano
H
H
Department of Microbiology, School of Medicine and Environmental Infectious Disease, Graduate School of Medical Sciences, Kitasato University, Sagamihara, Kanagawa 228-8555, Japan. d300042c@stcc.nagasaki-u.ac.jp
Kuga
A
A
Okamoto
R
R
Kitasato
H
H
Kobayashi
T
T
Inoue
M
M
D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000378:metabolism / Q000494:pharmacology*; D001426:Bacterial Proteins; D001483:Base Sequence; D004269:DNA, Bacterial / Q000032:analysis; D006801:Humans; D000077731:Meropenem; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D010957:Plasmids / Q000235:genetics; D016868:Serratia Infections / Q000382:microbiology; D012706:Serratia marcescens / Q000187:drug effects / Q000201:enzymology*; D013379:Substrate Specificity; D013845:Thienamycins / Q000378:metabolism / Q000494:pharmacology*; D001618:beta-Lactamases / Q000235:genetics* / Q000378:metabolism
D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004269:DNA, Bacterial; D013845:Thienamycins; D001618:beta-Lactamases; D000077731:Meropenem