Are E-test and Vitek2 good choices for tigecycline susceptibility testing when comparing broth microdilution for MDR and XDR Acinetobacter baumannii?

This study reports the results of antimicrobial susceptibility testing of 10 MDR and 74 XDR Acinetobacter baumannii clinical isolates from our hospital routine. We used three different methods: two automated systems (Sensititre and VITEK 2) and one standardized manual method (E-test). Since many published papers refer to in vitro tests performed by E-test, the aim of this study was to test if this method is reliable for testing tigecycline. The results obtained show that E-test significantly overestimates the MIC of the broth microdilution (reference test), thus obtaining a significant number of major errors (resistant instead of sensitive). VITEK 2 also shows the same problem, but it is less critical. We therefore conclude that these methods do not seem to be very reliable in the performance of susceptibility testing of MDR and XDR Acinetobacter baumannii against tigecycline.