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).