Wednesday, November 16, 2016

Tuberculosis-causing bacteria geographically restricted

Scimex: The bacteria responsible for causing human tuberculosis (Mycobacterium tuberculosis) is genetically diverse and has evolved multiple lineages throughout the world. Some lineages appear to adapt to particular human populations, but of the seven human lineages, only one - lineage 4 - exists on all continents. A global genetic study published in Nature and including New Zealand data has looked at why lineage 4 was so globally successful when other lineages are so geographically restricted. The study found that lineage 4 bacteria were mainly ‘generalists’ rather than ‘specialists’, and therefore filled a larger ecological niche.

Generalist and specialist species differ in the breadth of their ecological niches. Little is known about the niche width of obligate human pathogens. Here we analyzed a global collection of Mycobacterium tuberculosis lineage 4 clinical isolates, the most geographically widespread cause of human tuberculosis. We show that lineage 4 comprises globally distributed and geographically restricted sublineages, suggesting a distinction between generalists and specialists. Population genomic analyses showed that, whereas the majority of human T cell epitopes were conserved in all sublineages, the proportion of variable epitopes was higher in generalists. Our data further support a European origin for the most common generalist sublineage. Hence, the global success of lineage 4 reflects distinct strategies adopted by different sublineages and the influence of human migration.