Phylogeographical and molecular characterization of an emerging Mycobacterium tuberculosis clone in Trinidad and Tobago.
Résumé
We report on a fine molecular and phylogenetical characterization of circulating Mycobacterium tuberculosis strains isolated from patients during a 1-year period in Trinidad and Tobago (T&T). The spoligotyping data coupled to minisatellite typing and available epidemiological data showed that a single major clone of "evolutionary modern" tubercle bacilli (SIT566) was responsible for more than half of the tuberculosis (TB) cases. It preferentially infected younger age groups (mean 39.1 years versus 47.7 years for other genotypes, p<0.0005), and was overrepresented in Port-of-Spain (1 out of 3 patients). A comparison of genotyping results to data gathered for 6 Caribbean countries (n=2653 clinical isolates) showed that the overall lineage distribution in T&T was completely different from its neighbors, e.g., T&T was the only country harboring a unique sublineage of the Latin American & Mediterranean (LAM) family, designated LAM-10CAM with phylogeographical specificity for Cameroon and neighboring countries in West Africa; interestingly 3/4 of the patients within this group in T&T were African descendants. Similarly, strains belonging to East African Indian (EAI) lineage with phylogeographical specificity for the Indian subcontinent, were found in T&T (13% of all strains), but were absent among the neighboring countries. Although the predominant SIT566 was not yet detected elsewhere in the Caribbean, available information underlined that this genotype was already present in the United States as imported cases of disease among T&T-born patients. Characterization of SIT566 strains using 12-, 15- and 24-loci MIRU typing, and comparison of results to international databases showed that these isolates were characterized by a common 12-loci MIRU pattern 224315153324 corresponding to MIRU International Type-MIT633 in 21/25 strains tested, as well as its 4 variants; an orphan pattern , MIT27-, MIT117-, and MIT1158-. Extended 24-loci MIRU typing led to a predominant pattern 224315153324323483334323 in a total of 16/21 MIT633 isolates, as well as identification of 3 supplemental patterns. Comparison of 24-loci MIRU data with the international database MIRU-VNTRplus showed the unique nature of the patterns obtained in T&T. Further analysis using the Levenshtein algorithm showed that the first 2 closest matches with the SIT566/MIT633 clone belonged to the X lineage strains in MIRU-VNTRplus. This observation corroborates our preliminary spoligotyping-based analysis using minimum spanning and neighbor-joining trees, which suggested a phylogenetical relatedness of the SIT566 clone with SIT119, which represents X1 lineage prototype in SpolDB4 database. We hypothesize that the predominant SIT566 clone might have evolved from a pool of X lineage M. tuberculosis strains with phylogeographical affinity for Anglo-Saxon descendants.