Microbial isolation and emergence of antimicrobial resistance associated with tigecycline usage.

BACKGROUND With the increasing experience of tigecycline usage, its ecological impact on microorganisms raises concerns but remains unknown. We aimed to analyze the difference in microorganisms isolated before, during, and after tigecycline usage and their susceptibility to antimicrobial agents. METHODS Between July 2008 and August 2009, 66 patients who received tigecycline monotherapy for more than 2 days at a Taiwan medical center were enrolled. Antimicrobial susceptibility testing was performed by broth microdilution method with VITEK-2 system and was analyzed according to the Clinical and Laboratory Standards Institute guidelines, except for tigecycline. We followed USA Food and Drug Administration criteria for interpretation of susceptibility to tigecycline. RESULTS The median duration of tigecycline monotherapy was 13.4 days. After tigecycline treatment, the isolation frequency of Acinetobacter baumannii, methicillin-resistant Staphylococcus aureus, Escherichia coli, and Klebsiella pneumoniae decreased, but that of Pseudomonas aeruginosa, Proteus sp, and Stenotrophomonas maltophilia did not change. A baumannii and P aeruginosa were the two most common pathogens when tigecycline was administered. The tigecycline susceptibility rate of A baumannii isolates decreased after the administration of tigecycline. CONCLUSION The most common pathogens isolated in patients receiving tigecycline were A baumannii and P aeruginosa. Tigecycline usage decreased the isolation frequency of A baumannii, methicillin-resistant S aureus, E coli, and K pneumoniae. Exposure to tigecycline may be associated with a decreased susceptibility rate of A baumannii for tigecycline.