Changes in MIC Within a Global Collection of Acinetobacter baumannii Collected as Part of the Tigecycline Evaluation and Surveillance Trial, 2004 to 2009

Background: The Tigecycline Evaluation and Surveillance Trial (T.E.S.T.) began in 2004 to monitor global antimicrobial susceptibility to tigecycline and a range of comparator antimicrobials among gram-positive and gram-negative organisms. Objective: The aim of this study was to report changes in MIC for tigecycline and other antimicrobial agents among 10,149 Acinetobacter baumannii isolates collected globally between 2004 and 2009. Methods: MICs of 10,149 isolates were determined locally using Clinical Laboratory and Standards Institute (CLSI) methodologies. Antimicrobial susceptibility was ascertained according to CLSI interpretive criteria (no interpretive criteria have been approved for tigecycline against Acinetobacter spp). Results: Increases in resistance were noted for most antimicrobial agents in all regions. Significant (P < 0.05) increases in percentage resistance were reported for all antimicrobial agents globally. The smallest changes in cumulative geometric mean MICs were reported for tigecycline (0.2 mg/L) and cefepime (3.5 mg/L). MIC90s were at the top of their testing ranges for most agents against both multidrug-resistant (MDR) and non-MDR isolates; only tigecycline showed little change in MIC90 between MDR (2 mg/L) and non-MDR (1 mg/L) isolates. Resistance was higher among isolates from the intensive care unit (ICU) compared with non-ICU isolates. Conclusion: These findings suggest that resistance is increasing among clinical isolates of A baumannii globally. Although resistance to tigecycline has been reported in the treatment of infections caused by A baumannii, it retains in vitro activity against this pathogen. i.