Association of Amino Acid Substitutions in Penicillin-Binding Protein 3 with β-Lactam Resistance in β-Lactamase-Negative Ampicillin-Resistant <i>Haemophilus influenzae</i>

Antimicrobial Agents and Chemotherapy - Tập 45 Số 6 - Trang 1693-1699 - 2001
Kimiko Ubukata1,2, Yumi Shibasaki2, Kentarou Yamamoto2, Naoko Chiba2, Keiko Hasegawa2, Yasuo Takeuchi2, Keisuke Sunakawa3, Matsuhisa Inoue4, Masatoshi Konno5
1Institute of Microbial Chemistry, Kamiohsaki, Shinagawa-ku,2 and
2Pharmaceutical Research Center, Meiji Seika Kaisha, Ltd., 760 Morookacho, Kohoku-ku, Yokohama,1
3Department of Infectious Diseases3 and
4Department of Bacteriology,4 School of Medicine, Kitasato University, Kitasato, Sagamihara, Japan
5Teikyo University School of Medicine,5Tokyo, and

Tóm tắt

ABSTRACT The affinity of [ 3 H]benzylpenicillin for penicillin-binding protein (PBP) 3A was reduced in 25 clinical isolates of β-lactamase-negative ampicillin (AMP)-resistant (BLNAR) Haemophilus influenzae for which the AMP MIC was ≥1.0 μg/ml. The affinities of PBP 3B and PBP 4 were also reduced in some strains. The sequences of the ftsI gene encoding the transpeptidase domain of PBP 3A and/or PBP 3B and of the dacB gene encoding PBP 4 were determined for these strains and compared to those of AMP-susceptible Rd strains. The BLNAR strains were classified into three groups on the basis of deduced amino acid substitutions in the ftsI gene, which is thought to be involved in septal peptidoglycan synthesis. His-517, near the conserved Lys-Thr-Gly (KTG) motif, was substituted for Arg-517 in group I strains ( n = 9), and Lys-526 was substituted for Asn-526 in group II strains ( n = 12). In group III strains ( n = 4), three residues (Met-377, Ser-385, and Leu-389), positioned near the conserved Ser-Ser-Asn (SSN) motif, were replaced with Ile, Thr, and Phe, respectively, in addition to the replacement with Lys-526. The MICs of cephem antibiotics with relatively high affinities for PBP 3A and PBP 3B were higher than those of AMP and meropenem for group III strains. The MICs of β-lactams for H. influenzae transformants into which the ftsI gene from BLNAR strains was introduced were as high as those for the donors, and PBP 3A and PBP 3B showed decreased affinities for β-lactams. There was no clear relationship between 7-bp deletions in the dacB gene and AMP susceptibility. Even though mutations in another gene(s) may be involved in β-lactam resistance, these data indicate that mutations in the ftsI gene are the most important for development of resistance to β-lactams in BLNAR strains.

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Antimicrobial Agents and Chemotherapy

Tập 45 Số 6

1693-1699

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