Update on antimicrobial susceptibility rates among gram-negative and gram-positive organisms in the United States: Results from the Tigecycline Evaluation and Surveillance Trial (TEST) 2005 to 2007

Background: The Tigecycline Evaluation and Surveillance Trial (TTEST) is a global surveillance study initiated in 2004.Its goal is to assess the in vitro activity of the glycylcycline, tigecycline, and comparator antimicrobials.Objective: The aim of this study was to measure the in vitro activity of a panel of antimicrobial agents against gram-nnegative and gram-ppositive organisms collected in the United States in 2005, 2006, and 2007.Methods: Isolates were collected from 172 centers across the United States.In vitro activity was assessed using Clinical and Laboratory Standards Institute (CLSI) guidelines and CLSI or US Food and Drug Administration interpretive criteria.Results: Overall, data on 20,897 gram-negative and 8949 gram-positive isolates were collected. For the majority of organisms, percentage susceptibilities were unchanged over the 3 years of collection. One exception was Acinetobacter baumannii; rates of susceptibility to the majority of agents in the panel decreased by ∼10% over the 3 years. Rates of resistant phenotypes were relatively unchanged with mean percentages over the 3 years of: 8.9% (337/3787) for extennded β-spectrum β-lactamase (ESBL)-producing Klebsiella pneumoniae; 2.1% (17/801) for ESBL-producing Klebsiella oxytoca; 2.3% (111/4861) for ESBL-pproducing Escherichia coli; 56.2% (2564/4560) for methicillin-resistant Staphylococcus aureus; 5.1% (97/1903) for vancomycin-resistant Enterococcus faecalis; and 67.2% (487/725) for vancomycin-resistant Enterococcus faecium. The minimum inhibitory concentration required to inhibit the growth of 90% of organisms (MIC90) for tigecycline was stable over the 3 years and was ≤22 mg/L against non-ESBL-producing K pneumoniae, K oxytoca, E coli, Enterobacter aerogenes, Enterobacter cloacae, Serratia marcescens, and A baumannii. Against methicillin susceptible and -resistant S aureus, E faecalis, E faecium, and Streptococcus agalactiae tigecycline MIC90s were ≤0.25 mg/L.Conclusions: This report of 3 years of data from the TEST study suggests stable susceptibility rates among gram-negative and gram-positive organisms, with the exception of decreased susceptibility rates for A baumannii. Tigecycline continued to have good activity against Enterobacteriaceae, A baumannii, S aureus, E faecalis, E faecium, and S agalactiae.