Molecular epidemiology of Mycobacterium tuberculosis and its relevance to the surveillance and control of TB: an e-debate

Highly structured genetic diversity of the Mycobacterium tuberculosis population in Djibouti

Djibouti is an East African country with a high tuberculosis incidence. This study was conducted over a 2-month period in Djibouti, during which 62 consecutive patients with pulmonary tuberculosis (TB) were included. Genetic characterization of Mycobacterium tuberculosis, using mycobacterial interspersed repetitive-unit variable-number tandem-repeat typing and spoligotyping, was performed. The genetic and phylogenetic analysis revealed only three major families (Central Asian, East African Indian and T). The high diversity and linkage disequilibrium within each family suggest a long period of clonal evolution. A Bayesian approach shows that the phylogenetic structure observed in our sample of 62 isolates is very likely to be representative of the phylogenetic structure of the M. tuberculosis population in the total number of TB cases.

Genetic diversity among Mycobacterium tuberculosis isolates from Mexican patients

Forty-six isolates of the Mycobacterium tuberculosis complex were typified by PCR of the IS6110 region and by Mycobacterium bovis specific primers JB21/JB22. Isolate MVG01 was typified as M. bovis, being the first record of a case of human tuberculosis caused by this species in Mexico. RAPD-PCR was used to describe the genetic diversity of the remaining 45 M. tuberculosis complex isolates. The corrected genotypic diversity value calculated for the analyzed population was 0.96, the estimated mean gene diversity was 0.235, and the corrected Shannon-Weiner index was 2.15. All allele-loci combinations generated showed significant linkage disequilibria. The distribution of genetic variation was analyzed both by the unweighted pair group method with arithmetic averages clustering and by principal coordinates analysis. Unweighted pair group method with arithmetic averages clustering resulted in a tree with four main clusters and one unclustered strain (MVG20), the principal coordinates analysis strain distribution pattern being consistent with this grouping. The obtained results suggest that the studied isolates belong to a clonal population having significant genetic diversity. Our genetic diversity results are comparable with those reported for other populations of M. tuberculosis, although only three RAPD primers were used.

Defining the mandate of tuberculosis research in a postgenomic era

The identification of Mycobacterium tuberculosis by Robert Koch in 1882 as the causative agent of tuberculosis, the release of the drug rifampicin in 1970 and the sequencing of the M. tuberculosis genome in 1998 are three major events that have revolutionized tuberculosis research. In spite of these breakthroughs, the continued status of tuberculosis as the largest killer amongst infectious diseases is an issue of major concern. Although directly observed short course chemotherapy exists to treat the disease, the emergence of drug-resistant strains has severely threatened the efficacy of the treatment. The recent sequencing of the M. tuberculosis genome holds promise for the development of new vaccines and the design of new drugs. This is all the more possible when the information from the genome sequence is combined with proteomics and structural and functional genomics. Such an integrated approach has led to the birth of a new field of research christened 'postgenomics' that holds substantial promise for the identification of novel drug targets and the potential to aid the development of new chemotherapeutic compounds to treat tuberculosis. The challenge before the scientific community therefore lies in elucidation of the wealth of information provided by the genome sequence and its translation into the design of novel therapies for the disease. All the major developments in the field of tuberculosis research after the sequencing of the M. tuberculosis genome will be discussed in this review.