S. Flexneri

3187 Words Jul 6th, 2015 13 Pages
The evolution of multi drug resistant strain shigella sonnei from its ancestor E. Coli and predecessor S. Flexneri and its spread to Vietnam

Introduction
Shigella is a genus of Gram-negative, facultative anaerobic, nonspore-forming, nonmotile, rod-shaped bacteria. The genus is named after Kiyoshi Shiga, who first discovered it in 1897. The causative agent of human shigellosis, Shigella causes disease in primates, and is the only naturally found in humans and apes. Shigella is one of the leading bacterial causes of diarrhea worldwide and it is suggested that Shigella causes about 90 million cases of severe dysentery, with at least 100,000 of these resulting in death each year. Shigella originates from a human-adapted E. coli that has
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Most of these newly disseminated S. sonnei populations belonged to a single, globally distributed, multidrug-resistant (MDR) clade of S. sonnei lineage III, also referred to as Global III. Members of this clade are biotype g and carry a class II integrin, a insertion within the chromosome bearing MDR genes. Recent shifts have been reported in the dominant agents of bacterial dysentery, with S. sonnei replacing Shigella flexneri in Vietnam, Thailand, Malaysia, China, and several other countries undergoing economic development. The genomes of more than 250 S. sonnei isolates were examined in Vietnam over a 15 year period to investigate the microevolution of this pathogen during its establishment in the human population.
S. sonnei was introduced into Vietnam in the early 1980s, where it continued to evolve, spreading geographically to establish localized founder populations. The population in Ho Chi Minh City has undergone several localized clonal replacement events, during which a small number of microevolutionary changes have risen to dominance. These changes, induced by horizontal gene transfer and substitution mutations, demonstrate high-level antimicrobial resistance and the ability to kill other gut bacteria. This work provides an insight into the microevolution of an innovative human pathogen during its establishment in a new host population.
Methods
Several methods were used when determining

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