Activity of fosfomycin and comparison of several susceptibility testing methods against contemporary urine isolates

Elizabeth B. Hirsch, Brian R. Raux, Paola C. Zucchi, Yisu Kim, Christopher McCoy, James E. Kirby, Sharon B. Wright, George M. Eliopoulos

Research output: Contribution to journalArticlepeer-review

56 Scopus citations


Fosfomycin is recommended as first-line treatment for acute uncomplicated cystitis in women. It has demonstrated in vitro activity against a variety of pathogens; however, a paucity of data are available from the USA. We determined the susceptibility of a collection of urine isolates to fosfomycin and compared multiple methods of susceptibility testing. Consecutive non-duplicate Enterobacteriaceae, enterococci and Pseudomonas aeruginosa isolates were collected from the clinical microbiology laboratory between August 2013 and January 2014. Isolates represented hospitalised or emergency department patients with monomicrobial bacteriuria. Fosfomycin MICs were determined in duplicate, on separate days, by Etest and disk diffusion and results were compared with agar dilution. Nitrofurantoin and ciprofloxacin were used as comparators. MIC results were categorised using Clinical and Laboratory Standards Institute interpretive criteria for Escherichia coli and Enterococcus faecalis. Correlation between the three testing methods was evaluated. Overall susceptibility to fosfomycin was 94.4%, 93.5% and 87.9% by agar dilution, disk diffusion and Etest, respectively. Five fosfomycin-resistant isolates were identified, including two Morganella morganii, one P. aeruginosa, one Proteus mirabilis and one Enterobacter aerogenes. Across all organisms, rates of essential agreement, categorical agreement, minor errors, major errors and very major errors for Etest/disk diffusion compared with agar dilution were 77.3%/NA, 89.5/93.8%, 7.1/5.0%, 3.6/1.3% and 0/0%, respectively. Fosfomycin displayed fairly consistent activity against a majority of isolates collected when using the susceptibility breakpoint of 64 μg/mL. MICs for E. coli were particularly low (≤2 μg/mL). These data lend support to current guidelines that recommend fosfomycin as empirical first-line therapy for uncomplicated UTI.

Original languageEnglish (US)
Pages (from-to)642-647
Number of pages6
JournalInternational Journal of Antimicrobial Agents
Issue number6
StatePublished - Dec 1 2015

Bibliographical note

Funding Information:
The authors are grateful for the assistance of Joanna Dakos and the following members of the Beth Israel Deaconess Medical Center (BIDMC) Clinical Microbiology Laboratory (Boston, MA) for help in facilitating isolate collection: Karen Eichelberger, Matthew MacKechnie and Danny Dy. Funding: This study was funded in part by a Society of Infectious Diseases Pharmacists’ Young Investigator Research Award to EBH. Competing interests: CM has received unrelated research funding from Durata Therapeutics/Forest Pharmaceuticals/Actavis; EBH has received unrelated funding from Durata Therapeutics/Actavis; GME has consulted for unrelated work for Durata Therapeutics. All other authors declare no competing interests. Ethical approval: This study was approved by the Institutional Review Boards at Beth Israel Deaconess Medical Center (BIDMC) and Northeastern University (Boston, MA). Owing to the retrospective nature of the study, informed consent from patients was waived.

Publisher Copyright:
© 2015 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved.


  • Carbapenem-resistant Enterobacteriaceae
  • Multidrug-resistant
  • UTI
  • Uropathogens


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