Reduction in chlorhexidine efficacy against multi-drug-resistant Acinetobacter baumannii international clone II

Background Nosocomial infections caused by Acinetobacter baumannii international clone II (IC II) can cause severe clinical outcomes. Aim Differential evaluation of bactericidal efficacy of chlorhexidine gluconate (CHX) and benzethonium chloride (BZT) disinfectants against IC II and non-IC II isolates. Methods Minimum inhibitory concentrations (MICs) of CHX and BZT were determined for 137 A. baumannii IC II, 99 non-IC II and 69 non-baumannii isolates, further classified according to MIC values into disinfectant-reduced susceptible (DRS) and disinfectant-susceptible (DS) groups. Time-kill curves and minimum bactericidal concentrations (MBCs) were evaluated for representative isolates in each group. Results CHX and BZT MIC₉₀s for IC II isolates were 100 and 175 mg/L, respectively, but those for non-IC II and non-baumannii isolates were <100 mg/L. Nevertheless, time-kill curves indicated that CHX and BZT reduced live bacterial cell number by 5 log₁₀ for IC II and non-IC II isolates within 30 s when used at 1000 mg/L, comparable to practical use concentrations. CHX MBC at 30 s was 1000 mg/L for IC II and non-IC II isolates, and was not influenced by addition of 3% bovine serum albumin (BSA); BZT MBC at 30 s was 100 mg/L without BSA and increased up to 500 mg/L upon addition of BSA. No significant differences in BSA were found between DRS and DS isolates. Conclusion CHX and BZT were effective against Acinetobacter spp. including IC II at a concentration of 1000 mg/L and exposure for at least 30 s, but their concentrations should be considered carefully to ensure sufficient effects in both clinical and healthcare settings.