Antimicrobial susceptibility tests.

Susceptibilities to ticarcillin (TIC) (Sigma-Aldrich, St. Louis, MO, USA), cefotaxime (CTX) (A.G. Scientific, Inc., San Diego, CA, USA), ceftazidime (CAZ) (Sigma-Aldrich), ertapenem (ETP) (Sigma-Aldrich), imipenem (IPM) (Sigma-Aldrich), and meropenem (MEM) (A.G. Scientific, Inc.) were determined by microdilution in cation-adjusted Mueller-Hinton (MH) broth (Becton Dickinson) with inocula of 5 × 10⁵ CFU/ml, according to CLSI M07-A9 guidelines (24). All MICs were determined in triplicate on three separate occasions and the mode (with at least 6 of 9 data points in agreement) given as the final value. MIC distributions were compared with the EUCAST epidemiological cutoff (ECOFF) and clinical breakpoints for all antibiotics (25). Ticarcillin plus clavulanate (TIM) was measured by Etest (AB Biodisk, Solna, Sweden). Susceptibility to all antibiotics was measured in control isolates (see Table S1A and B in the supplemental material). CTX, ETP, TIC, and TIM were tested against isolates with bla_CMY-2-like and/or bla_TEM genes only (see Tables S2 to S4 in the supplemental material). CTX and ETP susceptibilities were measured in isolates with a bla_DHA gene (see Table S5 in the supplemental material). CTX, CAZ, and ETP were tested against isolates carrying bla_CTX-M (see Tables S6 and S7 in the supplemental material). Susceptibility to carbapenems (MEM, IPM, and ETP) was measured in isolates with a bla_IMP gene (see Table S8A and B in the supplemental material).