Nationwide Surveillance of in vitro Activities of Tigecycline against Clinical Isolates of Gram-Positive Bacteria in Taiwan: Broth Microdilution Method vs. the E test

Background: The Tigecycline In-Vitro Surveillance in Taiwan (TIST), initiated in 2006, is a nationwide surveillance program designed to monitor longitudinally the in vitro activities of tigecycline against commonly encountered resistant bacteria in Taiwan. This study, part of TIST-2006 study, aims to compare the in vitro activities of tigecycline against clinical isolates of Gram-positive bacteria. Methods: A total of 805 isolates of Gram-positive bacteria were collected from various sources of patients treated at 20 teaching hospitals. Minimum inhibitory concentrations (MICs) for tigecycline of these isolates were determined by the broth microdilution methods according the guidelines described by Clinical and Laboratory Standards Institute (CLSI) and the E test as manufacturer’s description. Susceptibility results of tigecycline were interpreted by the MIC criteria provided by U.S. FDA. Agreement and error analysis of results generated by two methods were also evaluated. Results: Susceptibility results of tigecycline are summarized in the table 1. Agreement of two methods was low: 70.8% for MRSA, 26.4% for S. pneumoiae, 20.5% for other Streptococcus species, and 30.7% for VRE. There was no very major or major error noted. Conclusion: Tigecycline exhibited excellent in vitro activities against gram-positive cocci, including MRSA, VRE, and penicillin-nonsusceptible S. pneumoiae (PNSSP) isolates in Taiwan. Correlations between MIC values using broth microdilution and the E test methods for these organisms were poor.