Antimicrobial effects of varied combinations of meropenem, sulbactam, and colistin on a multidrug-resistant Acinetobacter baumannii isolate that caused meningitis and bacteremia

Meropenem (MEM; 2 g/8 hr; minimum inhibitory concentration [MIC] = 256 mg/L) plus sulbactam (SUL; 1 g/8 hr; MIC = 128 mg/L) (two-drug-therapy period), and subsequent additional intravenous colistin (COL; 2.5 mg/kg/12 hr) and intraventricular (COL, 5 mg/day; MIC = 1 mg/L) (three-drug-therapy period) were sequentially used in a patient with postneurosurgery bacteremic meningitis due to a multidrug-resistant Acinetobacter baumannii (MDRAB) isolate (AB ₁). We detected 4- to 32-fold increases in peak or trough cerebrospinal fluid bactericidal titer and serum bactericidal titer in three-drug-therapy period when comparing to those in two-drug-therapy period. The time-kill study with MEM, SUL, and COL alone or varied combinations (all at 1 × MIC) against AB₁ and another genetically nonrelated MDRAB isolate (AB₁₃₄ [MICs of MEM = 64 mg/L, SUL = 16 mg/L, and COL = 1 mg/L]) was performed. The two-drug combinations (MEM + SUL, MEM + COL, and SUL + COL) each elicited different inhibitory effect on AB₁ and AB ₁₃₄ at 6 hr. Bacterial regrowth at 24 hr was observed in the experiments in which the MDRAB isolate was inhibited earlier by COL alone (AB₁ and AB₁₃₄), by MEM plus SUL (AB₁), and by MEM plus COL (AB₁₃₄), but not in SUL plus COL, and MEM + SUL + COL. Combined use of COL with MEM and/or SUL may provide good therapeutic options, even though MEM and SUL are in vitro resistance to the MDRAB.