Catch them young
doi:10.1038/nindia.2008.183 Published online 17 April 2008
A new opinionated analysis by Indian and German biologists suggests that if one catches pathogens while they are evolving inside humans or other hosts, one could make precise diagnostic tools for the diseases they cause by tracking their genome evolution.
Diagnostic development could target markers linked to identification of real-time genome evolution in pathogens. The biologists base their theory on the premise that many benign forms of such bacteria evolve into deadly pathogens by either acquiring new gene cassettes or by shredding their genomes. They could be identified to be ultimately eliminated or tamed if tracked early in their virulent pursuits.
Pathogenic bacteria keep recasting their genomes to fine tune themselves to their changing hosts. Such a dynamic change, essentially a trade-off between the bug and host shapes their genetic identity, functional versatility and chemical complexity. "As a result, different strains of the same species of bacteria have different disease potential and outcomes in different human communities in terms of transmission vigour or virulence," says senior author Seyed E. Hasnain.
Virulence-associated factors of bacterial pathogens are frequently encoded on mobile genetic elements, such as bacteriophages, plasmids and pathogenicity islands (PAIs). Some pathogenicity islands can delete spontaneously from the chromosome and may be transferred to other suitable recipients. PAIs contribute to bacterial genome fluidity and constitute, together with other mobile and accessory genetic elements, the 'plastic gene pool' of a given bacterial population. Such a 'dockyard' of extra DNA comprising 'flexible genome' which the bugs keep shuffling and bartering thus makes accurate diagnosis a problematic issue.
"Diagnostic implications of genome fluidity among many bacterial pathogens have been underestimated. It becomes more and more clear in the wake of comparative genomics that factors associated with virulence and fitness have frequently been acquired by horizontal gene transfer," says co-author Niyaz Ahmed.
- Ahmed, N. et al. Genomic fluidity and pathogenic bacteria: applications in diagnostics, epidemiology and intervention. Nat. Rev. Microbiol. 6, 387-394 (2008)