Fig. 1.

Double-disk synergy test with P. aeruginosa isolates producing the extended-spectrum oxacillinases OXA-16 and OXA-142 (OXA-10 derived), OXA-28 and OXA-183 (OXA-13 derived), or OXA-32 and OXA-161 (OXA-2 derived) or overproducing the cephalosporinase AmpC (AmpC). Distances between the disks were adapted to each strain, based on the inhibition zone diameter around disks containing each compound tested separately. For instance, if no inhibition zone was noticed around clavulanate- and ceftazidime-containing disks, the distance between their two disks is 5 ± 1 mm. Abbreviations: FEP, cefepime (30 μg); AMC, amoxicillin-clavulanate (20/10 μg); CAZ, ceftazidime (30 μg); IMP, imipenem (10 μg). Interpretative results are given (see Table 1).