Characterization of embB mutations involved in ethambutol resistance in multi-drug resistant Mycobacterium tuberculosis isolates in Zambia

Ethambutol (EMB) is an important anti-tuberculosis drug used in the management of multi-drug resistant tuberculosis (MDR-TB). Mutations in embB are the major mechanism of resistance. This study investigated embB mutations among MDR-TB isolates and analyzed their correlations with phenotypic drug susceptibility testing (DST) in Zambia. A total of 132 MDR-TB isolates were collected from January 2014 to April 2017 and characterized using MGIT 960 systems, embB sequencing, and spoligotyping. Out of 61 phenotypically EMB resistant isolates, 53 had mutations in embB. Among the 71 EMB susceptible isolates, 47 had embB mutations. Sensitivity of embB mutations was 86.9% while specificity was 33.8%. CAS1_Kili (SIT21) had high odds of having embB mutations, particularly, G918A (Met306eIl) (Odds ratio 16.7, p