What factors contribute to the long-term persistence of Shigella species as pathogens?

The genus Shigella is a globally important pathogen responsible for the infectious disease shigellosis which causes an estimated 125 million cases worldwide and up to 100 000 deaths. Shigella species are now recognised as a priority organism by the World Health Organisation due to the increasing antimicrobial resistance (AMR) observed. For adults, treatment of Shigella infections commonly consists of ciprofloxacin, however, recently there have been confirmed cases of ciprofloxacin-resistant strains. Most Shigella is already resistant to ampicillin and trimethoprim so added resistance to ciprofloxacin is a worrying development. Also of note is the role played by toxin-antitoxin systems where they are critical for maintaining large plasmids that typically contain genes of interest such as AMR genes and virulence factors. The Murray collection comprises of several hundred bacterial strains from the pre-antibiotic era (1917–1954) from a range of geographic locations. Within this collection there are many Shigella isolates which are now publicly available for analysis. There are also available datasets for modern collections which have been sequenced for past studies. We will use these data sets to perform bioinformatic analysis and characterise the dynamic changes in the genetic composition across time. The Murray Collection isolates provide a prospective from the pre-antibiotic era and so from the comparisons with modern isolates we will observe the effect of routine antibiotic use has on the evolution of antimicrobial resistance. Through this investigation the hope is to provide unprecedented insight into how AMR and toxin-anti-toxin systems contribute to the long-term persistence and success of Shigella.