Evaluation of Dot-Blot and Phage Replication Techniques for Detection of Drug Resistant Mycobacterium Tuberculosis

We have assessed the utility of two new methods; dot-blot and bacteriophage replication techniques; for use in a routine diagnosis laboratory in poor resource settings in the screening of drug resistant Mycobacteria tuberculosis by comparing with the conventional proportion method. A total of 145 M. tuberculosis clinical isolates were tested for resistance to rifampicin; isoniazid; streptomycin and ethambutol. The dot blot had sensitivities of 91.7; 100; 93.5and 85.7 and specificities of 99.2; 99.2; 99.1and 99.2 for rifampicin; streptomycin; isoniazid and ethambutol; respectively. The phage technique had sensitivities of 92and 84.6and specificities of 99.2and 99.2for rifampicin and streptomycin; respectively. Both techniques yielded results within 48 hours of receipt of the culture on solid media.The high sensitivity and specificity coupled with rapidity of results indicate that these methods are potentially useful tools for screening resistance to anti-tuberculosis drugs in our setting. However; the phage replication technique; which is simpler and technically less demanding; seems the most suitable for routine screening of drug resistant mycobacteria in resource deprived countries such as Tanzania. We are recommending further field evaluation of the phage replication method so that it can complement; and possibly replace; the conventional proportion method in drug susceptibility testing

Analysis for a limited number of gene codons can predict drug resistance of Mycobacterium tuberculosis in a high-incidence community.

Correct and rapid diagnosis is essential in the management of multidrug-resistant tuberculosis (MDR-TB). In this population-based study of 61 patients with drug-resistant tuberculosis, we evaluated the frequency of mutations and compared the performance of genotypic (mutation analysis by dot blot hybridization) and phenotypic (indirect proportion method) drug resistance tests. Three selected codons (rpoB531, rpoB526, and katG315) allowed identification of 90% of MDR-TB cases. Ninety percent of rifampin, streptomycin, and ethambutol resistance and 75% of isoniazid resistance were detected by screening for six codons: rpoB531, rpoB526, rrs-513, rpsL43, embB306, and katG315. The performance (reproducibility, sensitivity, and specificity) of the genotypic method was superior to that of the routine phenotypic method, with the exception of sensitivity for isoniazid resistance. A commercialized molecular genetic test for a limited number of target loci might be a good alternative for a drug resistance screening test in the context of an MDR "DOTS-plus" strategy.