Objective: To set up phage amplified biologically assay (PhaB) for rapid detection ethambutol (EMB) resistance and to evaluate the use of PhaB in the detection of EMB resistance.
Methods: To detect the EMB resistance of 138 clinical isolates of Mycobacterium tuberculosis (MTB) by PhaB and compare it with the results of BACTEC-960 system. The minimal inhibitory concentration (MIC) was detected for all the discrepant isolates.
Results: Of all the 138 strains of MTB clinical isolates, 114 strains were EMB-susceptible and 24 strains were EMB-resistant with BACTEC-960 system while 118 strains were EMB-susceptible and 20 strains were EMB-resistant with PhaB. 112 of the 138 strains were EMB-susceptible and 18 strains were EMB-resistant with the two methods. The concordant isolates in determination of EMB resistance were 130 strains in the two methods and the concordance rate was 94.2%. The disconcordant isolates were 8 strains and the discrepancy rate was 5.8%. The sensitivity, specificity, positive and negative predictive value as well as overall accuracy for the PhaB assay was 75.0% (18/24), 98.2% (112/114), 90.0% (18/20), 94.9% (112/118) and 94.2% (130/138) respectively if the judgment standard was adopted by BACTEC-960 method.
Conclusions: The PhaB assay can be used for detection of EMB resistance in isolates of MTB easily and quickly in three days. This method do not need special instrument and may be used in rapid screening method for EMB resistance of MTB.