Antimicrobial activities of piperacillin-tazobactam against Haemophilus influenzae isolates, including beta-lactamase-negative ampicillin-resistant and beta-lactamase-positive amoxicillin-clavulanate-resistant isolates, and mutations in their quinolone resistance-determining regions.
Beta-lactamase-negative ampicillin-resistant (BLNAR) isolates of Haemophilus influenzae have been emerging in some countries, including Japan. The Clinical and Laboratory Standards Institute has only a susceptible MIC breakpoint (< or = 1 microg/ml) for piperacillin-tazobactam and a disclaimer comment that BLNAR H. influenzae should be considered resistant, which was adapted without presentation of data. In addition, fluoroquinolone-resistant H. influenzae isolates have recently been occasionally reported worldwide. To address these problems, we examined susceptibilities to beta-lactams, including piperacillin-tazobactam, and ciprofloxacin by microdilution and disk diffusion (only for piperacillin-tazobactam) methods, against a total of 400 recent H. influenzae clinical isolates, including 100 beta-lactamase-negative ampicillin-susceptible, beta-lactamase-positive ampicillin-resistant, BLNAR, and beta-lactamase-positive amoxicillin-clavulanate-resistant (BLPACR) isolates each. BLNAR and BLPACR isolates were tested by PCR using primers that amplify specific regions of the ftsI gene. We also detected mutations in quinolone resistance-determining regions (QRDRs) by direct sequencing of the PCR products of DNA fragments. Among beta-lactams, piperacillin-tazobactam exhibited potent activity against all isolates of H. influenzae, with all MICs at < or = 0.5 microg/ml (susceptible). A disk diffusion breakpoint for piperacillin-tazobactam of > or = 21 mm is proposed. We confirmed that all BLNAR and BLPACR isolates had amino acid substitutions in the ftsI gene and that the major pattern was group III-like (87.5%). One ciprofloxacin-resistant isolate (MIC, 16 microg/ml) and 31 ciprofloxacin-susceptible isolates (MICs, 0.06 to 0.5 microg/ml) had amino acid changes in their QRDRs. Piperacillin-tazobactam was the most potent beta-lactam tested against all classes of H. influenzae isolates. It is possible that fluoroquinolone-resistant H. influenzae will emerge since several clinical isolates carried mutations in their QRDRs.
Hirakata
Yoichi
Y
Department of Infection Control and Laboratory Diagnostics, Tohoku University Graduate School of Medicine, Aoba-ku, Sendai, Miyagi 980-8574, Japan. hiraichi@mail.tains.tohoku.ac.jp
Ohmori
Kaori
K
Mikuriya
Miwako
M
Saika
Takeshi
T
Matsuzaki
Kaoru
K
Hasegawa
Miyuki
M
Hatta
Masumitsu
M
Yamamoto
Natsuo
N
Kunishima
Hiroyuki
H
Yano
Hisakazu
H
Kitagawa
Miho
M
Arai
Kazuaki
K
Kawakami
Kazuyoshi
K
Kobayashi
Intetsu
I
Jones
Ronald N
RN
Kohno
Shigeru
S
Yamaguchi
Keizo
K
Kaku
Mitsuo
M
D019980:Amoxicillin-Potassium Clavulanate Combination; D000667:Ampicillin / Q000494:pharmacology*; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002939:Ciprofloxacin / Q000494:pharmacology; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics; D006193:Haemophilus influenzae / Q000187:drug effects* / Q000235:genetics; D008826:Microbial Sensitivity Tests; D009154:Mutation; D001618:beta-Lactamases / Q000494:pharmacology*
D000900:Anti-Bacterial Agents; D002939:Ciprofloxacin; D019980:Amoxicillin-Potassium Clavulanate Combination; D000667:Ampicillin; D001618:beta-Lactamases