Molecular evolution of Mycobacterium tuberculosis

Abstract

Tuberculosis continues to be the main cause of death from a single infectious agent in developing countries. The causative agent, Mycobacterium tuberculosis, is thought to have diverged from its common ancestor as recently as 15,000 years ago. Subsequently, various genetic elements have evolved over time at different rates and can be used to elucidate patterns of infection. When individual elements are studied within genetic families, very low rates of variation are observed for almost every marker. For example, when all M. tuberculosis genetic families are considered, the number of alleles observed at each mycobacterial interspersed repetitive unit (MIRU) locus usually drops when viewed within a single genetic family, indicating that the rate of repeat variation may be low, as each member of that family is a descendant of a single common ancestor. Also, the low level of silent nucleotide variation observed indicates that M. tuberculosis is, in evolutionary terms, very young. Mapping the variation of the different markers used in molecular epidemiology within a genetic framework enables the relative rates of variation of these markers to be determined and, together with a complete chronology, allows the identification of more informative panels of markers tailored to individual genetic families.

Variation in Gamma Interferon Responses to Different Infecting Strains of Mycobacterium tuberculosis in Acid-Fast Bacillus Smear-Positive Patients and Household Contacts in Antananarivo, Madagascar

“…However, there was some association of specific IS6110-RFLP patterns with disease presentation, suggesting that some strains may have the ability to disseminate more easily than others. Similarly, studies performed in Vietnam reported that the Euro-American lineage (corresponding to the modern group 2 strains [5]) associated with radiographically detected lung consolidation in pulmonary TB patients was more likely to result in pulmonary TB than meningeal TB (59) and less likely to cause extrapulmonary disease (12). In The Gambia, contacts exposed to Beijing strains were most likely to develop TB disease (14).…”

“…The strain distribution was similar to that described in a previous study (24). Then, for the analysis, we considered the phylogeny described elsewhere (5,9), where the M. tuberculosis strains were divided into an "ancient" strain group (spoligotypes of the East African-Indian [EAI] family) and a "modern" strain group, with modern group 1 including the Beijing and Central Asian (CAS) families and modern group 2 containing the T (undefined family), Haarlem, LAM, U, X, and S families (Fig. 1B).…”

Genome-Wide Sequence Variation among Mycobacterium avium Subspecies paratuberculosis Isolates: A Better Understanding of Johne?s Disease Transmission Dynamics

“…SNPs within this gene could likely be an indication of common evolutionary ancestor with environmental isolates. Similarity, SNPs in cytochrome P450 enzymes (Table 5) that catalyze mixed oxidation of hydrophobic compounds associated with free-living saprophyte (Arnold, 2007), another indication of a common environmental ancestor for M. ap . Finally, genes encoding cytochrome P450 were shown to play a role in the persistence of M. tuberculosis in tissues (McLean et al, 2010).…”

Mycobacterium tuberculosis mutants with multidrug resistance: History of origin, genetic and molecular mechanisms of resistance, and emerging challenges

“…Finally, the acquisition of drug resistance depends on the MT subgroup. Beijing type strains are relatively abundant among MDR and XDR strains (for a review of the other features of such strains, see [3]). An attempt was made to hypothesize that the fact that such strains tend to acquire MDR is associated with their higher mutability, but the frequency of spontaneous rifampi cin resistance mutations in vitro was the same as in other MT types [102].…”

“…All of the MTC members are subspecies of one species, which is also termed MT. There are seven such subspecies (M. tuberculosis, M. africanum, M. bovis, M. caprae, M. pinnipedi, M. microti, and M. cannettii, also known as M. prototuberculosis), which have the same charac teristics of the 16S rRNA genes and differ only in structure of certain genome regions [2,3]. MT (earlier referred to as M. tuberculosis hominis) is the most sig nificant for medicine.…”