Molecular Characteristics of Strains of the Cameroon Family, the Major Group of Mycobacterium tuberculosis in a Country with a High Prevalence of Tuberculosis

Abstract

A preliminary investigation of the genetic biodiversity of Mycobacterium tuberculosis complex strains in Cameroon, a country with a high prevalence of tuberculosis, described a group of closely related M. tuberculosis strains (the Cameroon family) currently responsible for more than 40% of smear-positive pulmonary tuberculosis cases. Here, we used various molecular methods to study the genetic characteristics of this family of strains. Cameroon family M. tuberculosis strains (i) are part of the major genetic group 2 and lack the TbD1 region like other families of epidemic strains, (ii) lack spacers 23, 24, and 25 in their direct repeat ( Molecular epidemiology methods revolutionized the fields of research, prevention, and control of tuberculosis (TB), allowing the differentiation between strains, assessment of the overall diversity of Mycobacterium tuberculosis complex strains including differences by region and population, and measurement of the prevalence of endemic strains (28). However, few molecular epidemiological studies have been conducted in countries with a high incidence of TB. The available data suggest that families of closely related strains are common in these areas (12). The "Beijing family" is one of the most well-known families, highly prevalent in East Asia and widespread around the world (11).Molecular analysis based on several variable genomic regions is required for a good definition of strains belonging to different families. Restriction fragment length polymorphism (RFLP) analysis based on the insertion sequence IS6110 results in a unique genotype since both the number of copies of this genetic element and its positions in the genome are variable (25,26). Precise IS6110 insertion site mapping provides additional information on the fitness of the strain (1) given that IS6110 insertion can modify the expression of the gene involved. Another genetic element useful for characterizing tubercle bacilli is the direct repeat (DR) locus (13), a polymorphic insertion preferential locus (ipl) for IS6110. DR polymorphism can be analyzed by spoligotyping, a method involving PCR-reverse hybridization (14). The DR locus is likely to evolve more slowly than IS6110, making spoligotyping less adequate than IS6110-RFLP for discriminating strains but more convenient for investigating the biogeographic distribution of families of M. tuberculosis complex strains (32). Variable-number tandem repeats, named mycobacterial interspersed repetitive units (MIRU-VNTR), are another type of variable element in the M. tuberculosis complex genome showing extensive polymorphism (17) with a discrimination power close to that of IS6110-RFLP (6). Because of their stability, they can be used for a clear definition of families of tubercle bacilli as well.Strains of the M. tuberculosis complex exhibit very little genome sequence diversity except in repeat sequences. Consequently, insignificant and rare genome alterations inherited and maintained through long-term evolution can be of phylogenetic value. On the basis of polymorphi...

Molecular Analysis of Human and Bovine Tubercle Bacilli from a Local Setting in Nigeria

“…The spoligotype pattern of this dominant strain is characteristic of the Cameroon family of M. tuberculosis strains (deletion of spacers 23 to 25 [13]). All but four isolates of this common strain share the same VNTR pattern (4-2-4-3*-3-3.1).…”

Discovery of a Novel Mycobacterium tuberculosis Lineage That Is a Major Cause of Tuberculosis in Rio de Janeiro, Brazil

“…Indeed, PE/PPE genes have been reported to be the main source of variation between M. tuberculosis strains and other MTC species in whole-genome comparisons (21) and are known to be overrepresented among the MTC genomic LSPs detected to date (21,44,47). Some PPE genes have been shown to be independently deleted or modified in multiple MTC species and lineages of M. tuberculosis (31): (i) PPE55 and PPE56 have been lost in Mycobacterium microti and Mycobacterium pinnipedii as a result of the MiD3 LSP and in M. bovis strain AF2122/97 via frameshifting (24,31); (ii) a PPE55 fragment has been shown to be highly polymorphic in "M. canettii" (31); and (iii) the PPE55 gene is disrupted by an IS6110 element in a sublineage of the Cameroon M. tuberculosis family (31,44). Moreover, PPE55 and PPE56 are known to be induced in M. tuberculosis both in vivo, in a murine model of TB (60), and in vitro, when mycobacteria were phagocytosed by gamma interferon-activated-macrophages (61).…”

Polymorphic Exact Tandem Repeat A (PETRA): a Newly Defined Lineage ofMycobacterium tuberculosisin Israel Originating Predominantly in Sub-Saharan Africa

“…A similar situation was recently described in which a Mycobacterium tuberculosis RD lineage was a major cause of tuberculosis in Rio de Janeiro, Brazil (43), and was subsequently found to be globally disseminated (27) as a sublineage of the Latin American-Mediterranean (LAM) Mycobacterium tuberculosis spoligotype lineage. MIRU-VNTR combined with spoligotyping was recently used to define a new Mycobacterium tuberculosis lineage responsible for over 40% of smear-positive pulmonary tuberculosis cases in Cameroon during the time period of the study (51).…”