Thierry Naas*2 , Bruno Coignard†2, Anne Carbonne‡, Karine Blanckaert‡, Odile Bajolet§, Claude Bernet¶, Xavier Verdeil#, Pascal Astagneau‡, Jean-Claude Desenclos†, Patrice Nordmann*, and on behalf ofthe French Nosocomial Infection Early Warning, Investigation and Surveillance Network
Author affiliations: *Hôpital de Bicêtre, Le Kremlin-Bicêtre, France; †Institut de Veille Sanitaire, Saint-Maurice, France; ‡Centre de Coordination de Lutte contre les Infections Nosocomiales Paris Nord, Paris, France; §Réseau Bactéries Multi-Résistantes Champagne-Ardennes, Centre Hospitalier et Universitaire, Reims, France; ¶Centre de Coordination de Lutte contre les Infections Nosocomiales Sud-Est, Lyon, France; #Centre de Coordination de Lutte Contre les Infections Nosocomiales Sud-Ouest et Centre Hospitalier et Universitaire, Toulouse, France
Figure 3. Extended-spectrum β-lactamase (ESBL) laboratory identification. Usefulness of double-disk synergy test with blaVEB-1-positive Acinetobacter baumannii strain on Mueller-Hinton agar plates with clavulanate as inhibitor. The disks tested contained ticarcillin + clavulanate (TCC), amoxicillin + clavulanate (AMC), moxalactam (MOX), ceftazidime (CAZ), and cefepime (FEP). A) Standard disk diffusion as recommended by Clinical and Laboratory Standards Institute at 37°C (98°F). B) Standard disk diffusion on cloxacillin-containing Mueller-Hinton plates at 37°C (98°F). Cloxacillin inhibits partially the naturally occurring cephalosporinase (AmpC) from A. baumannii, thus enabling easier detection of possible ESBL phenotypes. C) Standard disk diffusion at 25°C (77°F). D) Standard disk diffusion at 25°C (77°F) when AMC and FEP disks were brought closer. The presence of ESBL was shown by a synergy image, as indicated with the arrows. ESBL presence was best seen on cloxacillin-containing (B) plates or at reduced growth temperature (D).
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