Antimicrobial susceptibility among Acinetobacter calcoaceticus-baumannii complex and Enterobacteriaceae collected as part of the Tigecycline Evaluation and Surveillance Trial

Objective: To measure the in vitro activity of a panel, of antimicrobial agents against gram-negative pathogens collected from the nine census regions of the USA. Methods: Isolates were collected from 76 centers between January 2004 and September 2005. In vitro activity was assessed using CLSI guidelines and CLSI or FDA interpretive criteria. Results: The lowest overall antimicrobial susceptibilities for Acinetobacter calcoaceticus-baumannii complex isolates (n = 851) were detected in the Middle Atlantic and East South Central regions. Overall, 29.3% of A. calcoaceticus-baumannii complex isolates were multidrug-resistant (resistant to >= 3 antimicrobial classes). Tigecycline (2 mu g/mL) had the lowest MIC90 against this organism. Imipenem, tigecycline, and levofloxacin had tow MIC(90)s (0.25-4 mu g/mL) against Enterobacter spp. (n = 1557), although the MIC90 for levofloxacin was elevated for East South Central region isolates (>= 16 mu g/mL). Susceptibility to Levofloxacin among the E. coli isolates (n = 1785) ranged from 71.7% (Pacific) to 88.5% (New England). The prevalence of ESBL-producing K. pneumoniae (126/1460) varied from 1.7% of isolates (Pacific) to 21.2% (Middle Atlantic). ESBL-producing K. pneumoniae MICs were lowest for imipenem and tigecycline. Conclusions: Antimicrobial susceptibility varies among the census regions of the USA. The broad-spectrum in vitro activity of tigecycline may make it a suitable candidate for use in the empiric treatment of serious infections. (c) 2007 The British Infection Society. Published by Elsevier Ltd. All rights reserved.