TABLE 1.

MICs and MBCs for strains of Acinetobacter baumannii used in the modela

AntibioticMIC/MBC (μg/ml) for:
Strain A (Ipms)Strain D (Ipmi)Strain E (Ipmr)
Imipenem1/18/16512/512
Sulbactam2/644/64128/>128
Tobramycin128/2568/328/32
Rifampin8/88/88/8
Colistin0.5/0.50.5/10.5/2
  • a Ipms, imipenem susceptible; Ipmi, imipenem intermediate resistant; Ipmr, imipenem resistant. Ticarcillin, piperacillin, gentamicin, and amikacin showed MICs of >256 μg/ml for all the strains. Ceftazidime, cefepime, and ciprofloxacin showed MICs of >32 μg/ml. For tetracycline, MICs were >8 μg/ml for all the strains. MIC interpretative standards of resistance (μg/ml) obtained from NCCLS (34) were as follows: piperacillin, ≥128; ticarcillin, ≥128; sulbactam, ≥16 (in combination with ampicillin): ceftazidime, ≥32; cefepime, ≥32; imipenem, ≥16; gentamicin, ≥16; amikacin, ≥64; tobramycin, ≥16; tetracycline, ≥16; ciprofloxacin, ≥4. There are no data about rifampin for infections by gram-negative bacteria; this is the reason we used the same standard as for Staphylococcus aureus, ≥4. In the case of polymyxins, the NCCLS does not provide data of sensitivity (11); we used the concentration of ≥4 μg/ml to define resistance (6).