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Evaluation of the in vitro interaction of fosfomycin and meropenem against metallo-β-lactamase–producing Pseudomonas aeruginosa using Etest and time-kill assay
  1. Sanjida Jahan,
  2. Heather Davis,
  3. Deborah S Ashcraft,
  4. George A Pankey
  1. Infectious Disease Translational Research, Ochsner Clinic Foundation, New Orleans, Louisiana, USA
  1. Correspondence to Dr George A Pankey, Infectious Disease Translational Research, Ochsner Clinic Foundation, New Orleans, LA 70121, USA; gpankey{at}


Pseudomonas aeruginosa is a nosocomial pathogen containing various resistance mechanisms. Among them, metallo-β-lactamase (MBL)–producing Pseudomonas are difficult to treat. Fosfomycin is an older antibiotic that has recently seen increased usage due to its activity against a broad spectrum of multidrug-resistant organisms. Our aim was to evaluate the combination of fosfomycin and meropenem against 20 MBL-producing P. aeruginosa (100% meropenem-resistant and 20% fosfomycin-resistant) using both an Etest minimal inhibitory concentration (MIC): MIC method and time-kill assay. MICs for fosfomycin and meropenem were determined by Etest and by broth microdilution method for the latter. The combination demonstrated synergy by Etest in 3/20 (15%) isolates and 5/20 (25%) isolates by time-kill assay. Results from the Etest method and time-kill assay were in agreement for 14/20 (70%) of isolates. No antagonism was found. Comparing both methods, Etest MIC: MIC method may be useful to rapidly evaluate other antimicrobial combinations.

  • anti-bacterial agents
  • bacterial infections

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  • Presented at This data were presented at the American Federation for Medical Research, Southern Regional Meeting, abstract 522 (14 February 2020; New Orleans, LA, USA).

  • Contributors All authors contributed to the study planning and methods, review of data, and preparation of manuscript. SJ, HD, and DSA performed testing in laboratory.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Patient consent for publication Not required.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data availability statement All data relevant to the study are included in the article.

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