2001. Susceptibility of Aerococcus urinae to Fluoroquinolones: Broth Microdilution and Gradient Diffusion
Session: Poster Abstract Session: Diagnostics: Bacteria and Mycobacteria
Saturday, October 6, 2018
Room: S Poster Hall
  • Poster IDWeek FERoy.pdf (226.4 kB)
  • Background: Aerococcus urinae is an emerging urinary pathogen frequently identified by MALDI-TOF. It is generally susceptible to beta-lactams, however, its susceptibility pattern to fluoroquinolones (FQ) remains variable. The goals of this study were i) to evaluate the performance of the gradient diffusion method (Etest®) to determine FQ resistance compared with broth microdilution (BMD) and ii) to estimate the resistance rate of A. urinae towards FQ in Quebec hospitals.

    Methods: 207 consecutive isolates of A. urinae from urinary tract specimens originating from 5 hospitals in Quebec and Montreal were identified by MALDI-TOF (Vitek-MS and Bruker). All isolates were tested with the BMD and gradient diffusion methods. BMD was carried out in triplicate and was conducted in accordance with CLSI guidelines (M45-A3). Isolates with insufficient growth at 24h were reincubated and evaluated at 48h. The gradient diffusion method was carried out using Etest® strips on MH agar with 5% sheep blood.


    Of the 207 isolates of A. urinae, 52 (25%) gave uninterpretable results using the BMD method (insufficient growth = 20; trailing = 32). We obtained the following results for the remaining 155 isolates:

    Susceptible – n (%)

    Intermediate – n (%)

    Resistant – n (%)


    105 (67%)

    16 (10%)

    35 (23%)


    114 (74%)

    6 (4%)

    35 (23%)

    BMD readings were often complicated by noticeably poor growth. The categorical agreement of the Etest® was 83% for ciprofloxacin and 95% for levofloxacin. Four very major errors were identified in a preliminary manner on 11% (4/35) of the ciprofloxacin-resistant isolates and 11%(4/35) of the levofloxacin-resistant isolates. Agar dilution will be done to confirm these results.

    Conclusion: In our experience, the method recommended by the CLSI for A. urinae susceptibility testing of FQ presented several problems, including insufficient growth and difficult reading. The Etest® appears to be a promising method for susceptibility testing of FQ for urinary tract isolates, but will first require a further comparison with agar dilution methods. In our study, the rate of FQ non-susceptibility of A. urinae was 27% for levofloxacin and 33% for ciprofloxacin. Therefore, FQ cannot be empirically recommended for the treatment of urinary tract infections caused by A. urinae.

    Tammy Berteau, MD1, France-Émilie Roy, MD2, Julie Bestman-Smith, MD, PhD2, Simon Grandjean Lapierre, MD3, Jean Longtin, MD4, Simon-Frédéric Dufresne, MD, FRCPC5, Marc Christian Domingo, PhD6 and Jean-Michel Leduc, MD7, (1)Internal Medicine, University of Laval, Quebec, QC, Canada, (2)Medical Microbiology and Infectious Diseases, University of Laval, Quebec, QC, Canada, (3)Medical Microbiology and Infectious Diseases, Centre de Recherche du Centre Hospitalier de L’université de Montréal, Montreal, QC, Canada, (4)INSPQ, Montreal, QC, Canada, (5)Microbiology, Infectious Disease and Immunology, Hôpital Maisonneuve-Rosemont (CIUSS-EMTL), Montreal, QC, Canada, (6)Laboratoire de Santé Publique du Québec, Ste-Anne-de-Bellevue, QC, Canada, (7)Microbiology and Immunology, CHU Sainte-Justine, Montreal, QC, Canada


    T. Berteau, None

    F. É. Roy, None

    J. Bestman-Smith, None

    S. Grandjean Lapierre, None

    J. Longtin, None

    S. F. Dufresne, None

    M. C. Domingo, None

    J. M. Leduc, Biomérieux: Investigator , Research grant .

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