Background: Acinetobacter baumannii has been reported increasingly as a significant causative organism of various nosocomial infections, including hospital-acquired pneumonia (HAP). The aim of this study was to investigate the clinical characteristics of HAP induced by carbapenem-resistant A. baumannii (CRAB) in elderly patients and the in vitro antimicrobial effects of cefoperazone/sulbactam combination therapy.

Methods: Seventy-one elderly patients in the geriatric ward of the General Hospital of the People's Liberation Army (PLAGH) with CRAB-induced HAP were analyzed retrospectively. The checkerboard method was used to determine the in vitro drug sensitivity of 60 CRAB strains to antimicrobial combinations (cefoperazone/sulbactam with meropenem, minocycline, or levofloxacin). The occurrence of carbapenemase genes was detected by PCR.

Results: CRAB-induced HAP occurred mostly in patients with underlying diseases. Prior to onset, most patients had received antimicrobial therapies including broad-spectrum β-lactams, invasive mechanical ventilation, and catheterization. The 30-day survival rate was 95.1% in patients using cefoperazone/sulbactam, with or without combination with antimicrobial drugs, and 73.3% in patients not using cefoperazone/sulbactam (p<0.05). When cefoperazone/sulbactam was used in combination with minocycline, levofloxacin, and meropenem, minimum inhibitory concentrations MIC50 and MIC90 were reduced for each drug. The genes OXA-23 and OXA-51 were amplified in 96.7% of the strains, but the genes OXA-24, OXA-58, SIM, VIM, and IMP were not amplified.

Conclusions: CRAB-induced HAP occurred mostly in patients with anemia or decreased levels of serum albumin, but with elevated levels of C-reactive protein and creatinine. Cefoperazone/sulbactam in combination with minocycline, meropenem, and levofloxacin had a synergistic and additive in vitro bacteriostatic action on CRAB.