Trends in the susceptibility of clinically important resistant bacteria to tigecycline: results from the Tigecycline In Vitro Surveillance in Taiwan study, 2006 to 2010

Abstract

The Tigecycline In Vitro Surveillance in Taiwan (TIST) study, a nationwide, prospective surveillance during 2006 to 2010, collected a total of 7,793 clinical isolates, including methicillin-resistant Staphylococcus aureus (MRSA) (n = 1,834), penicillin-resistant Streptococcus pneumoniae (PRSP) (n = 423), vancomycin-resistant enterococci (VRE) (n = 219), extended-spectrum β-lactamase (ESBL)-producing Escherichia coli (n = 1,141), ESBL-producing Klebsiella pneumoniae (n = 1,330), Acinetobacter baumannii (n = 1,645), and Stenotrophomonas maltophilia (n = 903), from different specimens from 20 different hospitals in Taiwan. MICs of tigecycline were determined following the criteria of the U.S. Food and Drug Administration (FDA) and the European Committee on Antimicrobial Susceptibility Testing (EUCAST-2011). Among drug-resistant Gram-positive pathogens, all of the PRSP isolates were susceptible to tigecycline (MIC(90), 0.03 μg/ml), and only one MRSA isolate (MIC(90), 0.5 μg/ml) and three VRE isolates (MIC(90), 0.125 μg/ml) were nonsusceptible to tigecycline. Among the Gram-negative bacteria, the tigecycline susceptibility rates were 99.65% for ESBL-producing E. coli (MIC(90), 0.5 μg/ml) and 96.32% for ESBL-producing K. pneumoniae (MIC(90), 2 μg/ml) when interpreted by FDA criteria but were 98.7% and 85.8%, respectively, when interpreted by EUCAST-2011 criteria. The susceptibility rate for A. baumannii (MIC(90), 4 μg/ml) decreased from 80.9% in 2006 to 55.3% in 2009 but increased to 73.4% in 2010. A bimodal MIC distribution was found among carbapenem-susceptible A. baumannii isolates, and a unimodal MIC distribution was found among carbapenem-nonsusceptible A. baumannii isolates. In Taiwan, tigecycline continues to have excellent in vitro activity against several major clinically important drug-resistant bacteria, with the exception of A. baumannii.

Fig 1

Distributions of tigecycline MIC, MIC₅₀, and MIC₉₀ values among 1,645 isolates of A. baumannii (A) and 903 isolates of S. maltophilia (B) as determined by the broth microdilution method by year from 2006 to 2010.

Fig 2

Rates of susceptibility to tigecycline among A. baumannii isolates from 16 hospitals that continuously participated in the study from 2006 to 2010 in Taiwan. Numbers in the table are the number of A. baumannii isolates studied in each hospital from 2006 to 2010.

Fig 3

Distributions of MICs of tigecycline among 2,339 isolates of carbapenem-nonsusceptible A. baumannii (A) and 387 isolates of carbapenem-susceptible A. baumannii (B) as determined by the agar dilution method and interpreted using tigecycline MIC interpretive breakpoints for Enterobacteriaceae recommended by the FDA (susceptible [S], ≤2 μg/ml; intermediate [I], 4 μg/ml; and resistant [R], ≥8 μg/ml), 2008 to 2010.