The minimum inhibition concentration was determined by the disk diffusion method in the
Mueller-Hinton medium. This method allows for the determination of total levels of antibiotic resistance from typical colonies, thereby detecting the most resist phenotypes present and the results were separately interpreted by using the breakpoints from the CLSI guidelines (CLSI, 2005).
MICs of antimicrobial drugs were determined for the gram-negative bacilli by using an Etest assay (AB BIODISK, Solna, Sweden) on
Mueller-Hinton medium. MICs were 1 [micro]g/mL for cefotaxime, 1 [micro]g/mL for amoxicillin--clavulanic acid, 2-3 [micro]g/mL for vancomycin, 0.064 [micro]g/mL for imipenem, 4-5 [micro]g/mL for ceftazidime, 1 [micro]g/mL for amikacin, 3 [micro]g/mL for ciprofloxacin, and 0.047 [micro]g/mL for trimethoprim-sulfamethoxazole.