In vitro activity of various antibiotics against clinical strains of Legionella species isolated in Japan

Naoyuki Miyashita, Intetsu Kobayashi, Futoshi Higa, Yosuke Aoki, Toshiaki Kikuchi, Masafumi Seki, Kazuhiro Tateda, Nobuko Maki, Kazuhiro Uchino, Kazuhiko Ogasawara, Satoe Kurachi, Tatsuya Ishikawa, Yoshito Ishimura, Izumo Kanesaka, Hiroshi Kiyota, Akira Watanabe

Research output: Contribution to journalArticlepeer-review

6 Citations (Scopus)

Abstract

The activities of various antibiotics against 58 clinical isolates of Legionella species were evaluated using two methods, extracellular activity (minimum inhibitory concentration [MIC]) and intracellular activity. Susceptibility testing was performed using BSYEα agar. The minimum extracellular concentration inhibiting intracellular multiplication (MIEC) was determined using a human monocyte-derived cell line, THP-1. The most potent drugs in terms of MICs against clinical isolates were levofloxacin, garenoxacin, and rifampicin with MIC90 values of 0.015 μg/ml. The activities of ciprofloxacin, pazufloxacin, moxifloxacin, clarithromycin, and azithromycin were slightly higher than those of levofloxacin, garenoxacin, and rifampicin with an MIC90 of 0.03–0.06 μg/ml. Minocycline showed the highest activity, with an MIC90 of 1 μg/ml. No resistance against the antibiotics tested was detected. No difference was detected in the MIC distributions of the antibiotics tested between L. pneumophila serogroup 1 and L. pneumophila non-serogroup 1. The MIECs of ciprofloxacin, pazufloxacin, levofloxacin, moxifloxacin, garenoxacin, clarithromycin, and azithromycin were almost the same as their MICs, with MIEC90 values of 0.015–0.06 μg/ml, although the MIEC of minocycline was relatively lower and that of rifampicin was higher than their respective MICs. No difference was detected in the MIEC distributions of the antibiotics tested between L. pneumophila serogroup 1 and L. pneumophila non-serogroup 1. The ratios of MIEC:MIC for rifampicin (8) and pazufloxacin (2) were higher than those for levofloxacin (1), ciprofloxacin (1), moxifloxacin (1), garenoxacin (1), clarithromycin (1), and azithromycin (1). Our study showed that quinolones and macrolides had potent antimicrobial activity against both extracellular and intracellular Legionella species. The present data suggested the possible efficacy of these drugs in treatment of Legionella infections.

Original languageEnglish
Pages (from-to)325-329
Number of pages5
JournalJournal of Infection and Chemotherapy
Volume24
Issue number5
DOIs
Publication statusPublished - 2018 May

Keywords

  • Extracellular activity
  • Intracellular activity
  • Legionella species
  • Minimum extracellular concentration inhibiting intracellular multiplication (MIEC)
  • Minimum inhibitory concentration (MIC)

ASJC Scopus subject areas

  • Microbiology (medical)
  • Pharmacology (medical)
  • Infectious Diseases

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