Journal Article

Measurement of ampicillin, vancomycin, linezolid and gentamicin activity against enterococcal biofilms

Jonathan A. T. Sandoe, Joanne Wysome, Andrew P. West, John Heritage and Mark H. Wilcox

in Journal of Antimicrobial Chemotherapy

Published on behalf of British Society for Antimicrobial Chemotherapy

Volume 57, issue 4, pages 767-770
Published in print April 2006 | ISSN: 0305-7453
Published online February 2006 | e-ISSN: 1460-2091 | DOI: http://dx.doi.org/10.1093/jac/dkl013
Measurement of ampicillin, vancomycin, linezolid and gentamicin activity against enterococcal biofilms

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Background: Enterococci frequently cause biofilm infections but susceptibility of clinical isolates growing in biofilms has not been investigated. The minimum biofilm eradicating concentration (MBEC) has been suggested as a guide to treatment of biofilm infections. We measured an alternative endpoint, the minimum biofilm inhibitory concentration (MBIC) and compared the results with MIC and MBC.

Objectives: To compare the MIC, MBC and MBIC of ampicillin, vancomycin and linezolid against enterococcal biofilms, to assess the impact of additional gentamicin and correlate findings with clinical outcome.

Methods: MIC and MBC were measured using standard techniques. MBICs were measured using a modification of the Calgary biofilm device method. Fifty-eight enterococcal isolates from episodes of intravascular catheter-related bloodstream infection were tested.

Results: Tolerance to ampicillin, vancomycin and linezolid was seen in 93%, 100% and 93% of isolates, respectively. MIC90s of ampicillin, vancomycin and linezolid were all 4 mg/L for Enterococcus faecalis isolates. MBC90s of ampicillin, vancomycin and linezolid for E. faecalis isolates were 1024, >128 and 2048 mg/L, respectively. MBIC90s of ampicillin, vancomycin and linezolid for E. faecalis isolates were 8192, 4096 and 4096 mg/L, respectively. Results for Enterococcus faecium were similar for vancomycin and linezolid but this species was generally more resistant to ampicillin. Adding 10 mg/L gentamicin had a variable effect on MIC, MBC or MBIC, which was not predictable by gentamicin susceptibility on disc testing.

Conclusions: Very high concentrations of ampicillin, vancomycin and linezolid are required to inhibit enterococcal biofilms in vitro. Combining these agents with gentamicin significantly reduced MIC, MBC and MBIC against only a proportion of enterococcal isolates. No correlation between MBIC and outcome was found.

Keywords: Enterococcus; enterococci; susceptibility; intravascular catheter-related bloodstream infections

Journal Article.  2677 words. 

Subjects: Medical Oncology ; Critical Care

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