Shigella flexneri is the most common cause of bacterial dysentery in low-income countries. Despite this, S. flexneri remains largely unexplored from a genomic standpoint and is still described using a vocabulary based on serotyping reactions developed over half-a-century ago. Here we combine whole genome sequencing with geographical and temporal data to examine the natural history of the species. Our analysis subdivides S. flexneri into seven phylogenetic groups (PGs); each containing two-or-more serotypes and characterised by distinct virulence gene complement and geographic range. Within the S. flexneri PGs we identify geographically restricted sub-lineages that appear to have persistently colonised regions for many decades to over 100 years. Although we found abundant evidence of antimicrobial resistance (AMR) determinant acquisition, our dataset shows no evidence of subsequent intercontinental spread of antimicrobial resistant strains. The pattern of colonisation and AMR gene acquisition suggest that S. flexneri has a distinct life-cycle involving local persistence. DOI: http://dx.doi.org/10.7554/eLife.07335.001 eLife digest Dysentery is a disease in which the intestine becomes inflamed due to infection by bacteria, viruses or other microbes. Of the bacteria that can cause dysentery, bacteria called Shigella are most often responsible. Humans can acquire Shigella through contaminated food or water. Over the last century, improvements to sanitation combined with access to clean drinking water and better food hygiene have decreased the number of cases of dysentery in many countries. However, the disease continues to be common in low-income countries, especially in young children. One species of Shigella bacteria, called S. flexneri , causes far more cases of dysentry than other species of Shigella . Across the world, there are many different strains of S. flexneri , but it is not clear how these strains are related to each other, or how variable the genes that they carry are—known as genetic diversity. Here, Connor, Barker, Baker et al. used a technique called whole genome sequencing to map the evolutionary relationships of over 300 S. flexneri samples collected from around the globe over the past 100 years. This revealed that the bacterial strains can be split into seven groups that each have distinct geographic ranges and combinations of genes that enable the bacteria to infect humans. Many of the strains of bacteria within these groups seem to have colonized, and remained in, quite small geographic areas over long periods of time. This is different to other Shigella species, which appear to have spread between continents far more frequently over much shorter timescales. Connor, Barker, Baker et al.’s findings reveal that S. flexneri is more diverse than other Shigella bacteria, and suggest that the ability of strains to persist in local areas may have contributed to the species’ long-term success. These results point towards the importance of the provision of clean water in the fight against S. flexneri , and underline the need for a greater understanding of how disease-causing bacteria colonize and interact with the local environment. DOI: http://dx.doi.org/10.7554/eLife.07335.002
【저자키워드】 Genomics, Other, E. coli, dysentery, Shigella, Pathogen evolution,