Determination of Susceptibility Rates of Nosocomial Acinetobacter baumannii Isolates to Sulbactam by E-test Method

Abstract

Introduction: Bacteria of the genus Acinetobacter play an important role as causative agents of hospital-acquired infections. Multidrug-resistant Acinetobacter infections have increasingly been observed worldwide. In parallel with the increasing rate of infections, therapeutic options are becoming limited. Although the susceptibility rates are not exactly known, sulbactam alone or sulbactam with ampicillin play a part in combination therapies against Acinetobacter infections. This study aimed to determine the minimum inhibitory concentrations (MICs) of sulbactam against multidrug-resistant Acinetobacter baumannii strains using the E-test method and to deduce the susceptibility rates based on literature data. Materials and Methods: The study included 100 multidrug-resistant A. baumannii strains isolated from clinical samples obtained from patients hospitalized in intensive care units of the Ministry of Health Ankara Training and Research Hospital between June 15, 2011 and June 15, 2013. Antibiotic susceptibility testing and strain identification were performed using conventional methods and the VITEK 2 (bioMerieux SA, France) system. Resistance to three or more drugs was considered as multidrug resistance. MIC, MIC50, and MIC90 values (mu g/mL) of sulbactam against the 100 isolates were determined using the E test method. Since the breakpoint MIC of sulbactam against Acinetobacter had not been established, the susceptibility rates were estimated based on the MIC values reported in the literature (<= 4 or 8 mu g/mL). Results: The MIC values of sulbactam against the Acinetobacter isolates ranged widely (between 1 and 256 mu g/mL), and the MIC50 and MIC90 values were determined to be 12 and 96 mu g/mL, respectively. When 8 mu g/mL was considered as the susceptibility breakpoint, 44% of the isolates were found to be susceptible; however, the rate was only 21% when 4 mu g/mL was considered as the breakpoint. Conclusion: Based on its MIC values determined in our study, sulbactam appeared to be a promising agent for the treatment of infections caused by multidrug-resistant A. baumannii isolates. Nonetheless, more studies are needed, especially on its clinical effectiveness.