Objectives: Antibiotic susceptibility of Legionella pneumophila is poorly understood, with treatment of Legionnaires’ disease often based on empirical choice. The aim of this study was to determine the antibiotic susceptibility of L. pneumophila strains. Methods: Antibiotic susceptibility of 92 L. pneumophila strains isolated in England and Wales between 2007 and 2017 was determined using a microbroth dilution methodology for each agent tested. MICs and MBCs were determined and compared with published intracellular concentrations of each agent tested. Results: The MIC range of erythromycin was 0.06–1 mg/L, the MIC range of rifampicin was 0.0001 mg/L, the MIC range of ciprofloxacin was 0.004–0.25 mg/L and the MIC range of levofloxacin and moxifloxacin was 0.03–0.25 mg/L. The MBC range of erythromycin was 1–32 mg/L, but the MBC range of ciprofloxacin was the same as the MIC range. For levofloxacin and moxifloxacin the MBC range was elevated by one dilution and two dilutions, respectively. Typically, intracellular bronchial secretion concentrations of erythromycin might be expected to reach a suitable level to exceed the MIC range; however, 91 of 92 (98.9%) isolates had an MBC below the expected intracellular concentrations, which indicated erythromycin may have variable efficacy. MIC and MBC values of ciprofloxacin, levofloxacin and moxifloxacin were below achievable intracellular levels within bronchial secretions. Comparison of the MIC/MBC correlation showed very little clustering for erythromycin, but strong clustering for levofloxacin and to a lesser extent ciprofloxacin. Conclusions: Use of the MIC/MBC linkage analysis seems an appropriate way forward for antimicrobial susceptibility testing and supports current guidance recommending levofloxacin for the treatment of Legionnaires’ disease.
Bibliographical noteFunding Information:
We would like to thank NHS trusts in England and Wales for referring primary specimens and/or L. pneumophila isolates to PHE and for their participation in the study. We would also like to thank all the staff at the Respiratory and Vaccine Preventable Bacteria Reference Unit and Antimicrobial Resistance and Healthcare Associated Infections Unit at PHE for their support with this work. Dr Chalker is affiliated with the National Institute for Health Research Health Protection Research Unit (NIHR HPRU) in Respiratory Infections at Imperial College London in partnership with PHE. This project was funded by Public Health England.
This project was funded by Public Health England.
© The Author(s) 2018. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved.
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