Ampicillin sulbactam

Susceptibility to 13 antibiotics was determined by the disc diffusion method and using the ADAGIO™ Automated System (Bio-Rad, Hercules, CA, USA) as described. The antibiotics tested included ampicillin (10 µg), penicillin (6 µg), ampicillin/sulbactam (20 µg), chloramphenicol (30 µg), vancomycin (5 µg), teicoplanin (30 µg), streptomycin (300 µg), gentamicin (120 µg), ciprofloxacin (5 µg), levofloxacin (5 µg), quinupristin-dalfopristin (15 µg), linezolid (30 µg) and tigecycline (15 µg) (Bio-Rad, Hercules, CA, USA)]. Susceptibility to aminoglycosides, glycopeptides, quinolones and β-lactam antibiotics was also determined by an E-test (M.I.C. Evaluator™, OXOID, Basingstoke, UK). The methods and the interpretation of the results followed the CLSI guidelines [32 ]. Enterococcus faecalis ATCC 29212 and Staphylococcus aureus ATCC 25923 were used as control strains.

Isolation of E. coli was performed as follows: liquid aspirates were diluted approximately ×10⁶ fold with sterile PBS (phosphate saline buffer). Approximately 0.05 ml volume of feces were placed into 0.5 ml of sterile PBS, vortexed to homogeneity, an aliquot was diluted approximately ×10⁶ fold. Biopsy samples were vortexed in 0.2 ml of sterile PBS. For all samples, 0.1 ml of the resulting liquid was spread onto the Luria-Bertani agar plates. After overnight incubation on 37 °C, isolated colonies were identified with the Matrix Assisted Laser Desorbtion/Ionization (MALDI) Biotyper software (Bruker Daltonics, Germany) using the Microflex LT mass spectrometer (Bruker Daltonics, Germany). For DNA extraction, all E. coli strains were grown in the Luria-Bertani broth at 37 °C with shaking (200 RPM) overnight and collected by centrifugation. Samples and corresponding E. coli isolates are listed in Table 1.
The testing of susceptibility to ampicillin/sulbactam, ceftriaxone, cefotaxime, ceftazidime, cefepime, imipenem, meropenem, gentamicin, levofloxacin, and ciprofloxacin (all from Bio-Rad, USA) was performed by the disc-diffusion method using the Mueller-Hinton agar plates. The E. coli strain ATCC 25922 was used as a control. Current CLSI and EUCAST criteria were used for interpretation.