Regional variations in multidrug resistance among Enterobacteriaceae in the USA and comparative activity of tigecycline, a new glycylcycline antimicrobial

We report here on the activity of tigecycline and comparators against multidrug-resistant (resistant to >= 3 antimicrobial classes; MDR) Enterobacteriaceae from the USA collected between January 2004 and January 2006 as part of the Tigecycline Evaluation and Surveillance Trial (TEST). Nationally, 137 (5.9%) Escherichia coli, 174 (10.1%) Klebsiella pneumoniae, 4 (1.2%) Klebsiella oxytoca, 24 (4.9%) Enterobacter aerogenes, 126 (9.5%) Enterobacter cloacae and 20 (2.6%) Serratia marcescens isolates were MDR. Four isolates (two K. pneumoniae and two E. cloacae) were resistant to nine antimicrobials. Tigecycline performed well against MDR E. coli (MIC90 0.5 mu g/mL, 0% resistant) and K. pneumoniae (MIC90 4 mu g/mL, 9.2% resistant). A MIC90 of 8 mu g/mL was reported for tigecycline against the other MDR organisms studied here, notably lower than those of most comparators. (C) 2007 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved.