Concomitant Resistance to Ethambutol, Isoniazid and Rifampicin in Mycobacterium Tuberculosis Isolates from China

In order to investigate the characteristics of the ethambutol (EMB) in Mycobacterium tuberculosis (M. tuberculosis) 228 clinical cases were enrolled from the 2,129 isolates in the Beijing Tuberculosis and Thoracic Tumor Research Institute during 2009 and 2010. The results from the Drug susceptibility test (DST) showed that more than 63% of EMB-sensitive isolates and only 23.2% of EMB-resistant isolates were sensitive to both rifampicin (RIF) and isoniazid (INH). About 59% of EMB-resistant isolates and only 17% of EMB-sensitive isolates were using multidrug resistant tuberculosis (MDR-TB). Of all the 228 EMB-resistant isolates, 84 isolates had a high resistance. Of those 84 isolates, 50% were resistant to high levels of INH, while 75% were resistant to high levels of RIF. EMB-resistant isolates had broader anti-Tuberculosis drug spectrums (2.19 +/- 0.10) than the EMB-sensitive isolates (0.79 +/- 0.04). In total, 162 (71.1%) contained mutations at embB306. An increased percentage of the embB306 mutations was found in the high RIF-resistant, MDR isolates, rather than in the INH-resistant ones. The minimum inhibitory concentrations (MICs) of EMB were higher for the RFP/INH-resistant isolates than those of the RFP/INH-sensitive ones. In conclusion, resistance to EMB, INH and RIF concomitantly existed and were coadjutant. Furthermore, the high percentage of mutations at embB306 existed in RIF/INH-resistant isolates.