Analysis of Isoniazid, Streptomycin and Ethambutol resistance in Mycobacterium tuberculosis isolates from Morocco

BACKGROUND: Drug-resistant tuberculosis is a major problem worldwide. Based on the knowledge of specific mutations occurring in Mycobacterium tuberculosis genome, drug resistance can be detected earlier. The aim of this study was to determine the prevalence of the most common mutations associated with resistance to Isoniazid (INH), Streptomycin (SM) and Ethambutol (EMB) in Mycobacterium tuberculosis isolates from Morocco in order to select target mutations to develop tests for rapid detection of drug-resistant Mycobacterium tuberculosis Moroccan isolates. METHODOLOGY: A total of 199 M. tuberculosis isolates collected from the National Tuberculosis Reference Laboratory in Morocco were subject to katG, inhA, rrs, rpsL and emb mutation analysis by PCR probe-based assay. The genotypic results were then compared to drug susceptibility testing results for the corresponding drugs. RESULTS: Among 66 phenotypically INH resistant isolates, 80.3% (53/66) were found to be genotypically INH resistant from which 77.3% (51/66) and 3% (2/66) had respective mutations in katG315 and inhp-15 codons. Of the 58 phenotypically SM resistant isolates, genotypic SM resistance was confirmed in 17.2% (10/58) cases. Nucleotide mutations at codons 43 and 88 of rpsL gene and at codon 512 of rrs gene were found respectively in 12.1% (7/58); 1.7% (1/58) and 3.4% (2/58) of the phenotypically SM resistant Mycobacterium tuberculosis isolates. Finally, mutations at codon 306 of embB gene were identified in 42.3% (11/26) of Mycobacterium tuberculosis isolates phenotypically EMB resistant. CONCLUSION: This study showed that a large proportion of Mycobacterium tuberculosis resistant isolates from Morocco carry a large number of mutations in different codons (especially katG315, embB306 and rpsL43) of the corresponding genes associated with drug resistance. Thus, molecular analysis based on the identification of such mutations is useful but not fully sufficient to predict all drug resistance cases. Based on these results, rapid drug resistance genotyping can be used as an adjunct to the traditional culture based methods in reference laboratories.