Abstract
BackgroundThe potential of genetic testing to rapidly diagnose drug resistance has lead to the development of new diagnostic assays. However, prior to implementation in a given setting, the association of specific mutations with specific drug resistance phenotypes should be evaluated. The purpose of this study was to evaluate molecular markers in predicting drug resistance in the Central Region of Cameroon.ResultsFrom April 2010 and March 2011, 725 smear positive pulmonary tuberculosis patients were enrolled and all positive cultures were tested for drug susceptibility. A total of 63 drug resistant and 100 drug sensitive Mycobacterium tuberculosis complex clinical isolates were screened for genetic mutations in katG, inhA, ahpC, rpoB, rpsL, rrs, gidB and embCAB loci using DNA sequencing. Of the 44 isoniazid resistant (INHR) isolates (24 high level, 1 μg/ml and 20 low level, 0.2 μg/ml), 73% (32/44) carried the katG315 and/or the -15 inhA promoter mutations. Of the 24 high level INHR, 17 (70.8%) harbored katG315 mutation, 1 a point mutation (-15C → T) in the inhA promoter and 6 were (25.0%) wild types. Thus, for INHR high level detection, katG315 mutation had a specificity and a sensitivity of 100% and 70.8% respectively. Of the 20 low level INHR, 10 (50.0%) had a -15C → T mutation in the inhA promoter region, and 1 (2.2%) a -32G → A mutation in the ahpC promoter region. All of the 7 rifampicin resistant (RIFR) isolates carried mutations in the rpoB gene (at codons Ser531Leu (71.4%), His526Asp (14.3%), and Asp516Val (14.3%)). Of the 27 streptomycin resistant (SMR) isolates, 7 carried mutations at the rpsL and the gidB genes. 1 of the 2 ethambutol resistant (EMBR) isolates displayed a mutation in embB gene.ConclusionThis study provided the first molecular investigation assessing the correlation of phenotypic to genotypic characteristics on MTB isolates from the Central Region of Cameroon using DNA sequencing. Mutations on rpoB, katG315 and -15 point mutations in inhA promoter loci could be used as markers for RIF and INH -resistance detection respectively.
Highlights
The potential of genetic testing to rapidly diagnose drug resistance has lead to the development of new diagnostic assays
Analysis of INH -resistance associated mutation A total of 44 INHR (24 high level and 20 low level)) and 100 matched INHS sensitive control strains were screened for mutations at katG codon 315, the fabG1-inhA regulatory region, the inhA ORF, the oxyR-ahpC intergenic region by Désoxyribonucleic acid (DNA) sequence analysis
The katG315 mutations resulted in a change of the wildtype codon, AGC (Ser) to ACC (Thr) in 17 strains and AAC (Asn) in one strain
Summary
The potential of genetic testing to rapidly diagnose drug resistance has lead to the development of new diagnostic assays. Prior to implementation in a given setting, the association of specific mutations with specific drug resistance phenotypes should be evaluated. The purpose of this study was to evaluate molecular markers in predicting drug resistance in the Central Region of Cameroon. Multidrug resistant (MDR) TB and the recently-described extensively drug resistant (XDR) TB severely complicate the management and control of the disease worldwide [1,2]. Almost 8.8 million new cases of TB were reported in 2010, and 1.4 million deaths were attributed to the disease. Asia and Sub-Saharan Africa accounted for 85% of new cases of TB worldwide [3]. Of the 8.8 million incident cases in 2010, 1.1 million (13%) were among people living with HIV
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