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 >or=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, 131 (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 (MIC(90) 0.5 microg/mL, 0% resistant) and K. pneumoniae (MIC(90) 4 microg/mL, 9.2% resistant). A MIC(90) of 8 microg/mL was reported for tigecycline against the other MDR organisms studied here, notably lower than those of most comparators.