Abstract
It has long been accepted that Shiga toxin (Stx) only exists in Shigella dysenteriae serotype 1. However, in recent decades, the presence of Shiga toxin genes (stx) in other Shigella spp. have been reported. We screened 366 Shigella flexneri strains from Alberta, Canada (2003 to 2016) for stx and 26 positive strains were identified. These isolates are highly related with the majority originating from the Dominican Republic and three isolates with Haiti origin. Both phylogenetic and spanning tree analysis of the 26 Alberta and 29 stx positive S. flexneri originating from the U.S., France, Canada (Quebec) and Haiti suggests that there are geographic specific distribution patterns (Haiti and Dominican Republic clades). This study provides the first comprehensive whole genome based phylogenetic analysis of stx positive S. flexneri strains as well as their global transmission, which signify the public health risks of global spreading of these strains.
Highlights
Shigella is a genus of Gram-negative bacterium that can be transmitted to humans through contaminated food, water, or direct/indirect contact with an infected person
That outbreak strain originated from an enteroaggregative E. coli (EAEC) but later acquiring a Shiga-toxin-encoding phage and antibiotic resistance genes making it highly pathogenic [25]
It is still unknown whether acquisition of this stx1 phage has increased the pathogenicity of these Shigella strains; it is evident that stx1 positive S. flexneri has exceptionally high prevalence rates (60.9% observed in Alberta cases returning from Dominican Republic and 57.1% observed in residents in Haiti as shown above) suggesting the stx1 positive S. flexneri strains have established in Alberta and spread locally
Summary
Shigella is a genus of Gram-negative bacterium that can be transmitted to humans through contaminated food, water, or direct/indirect contact with an infected person. It was estimated that Shigella causes 188 million cases of disease and 164,300 deaths per year globally [5]
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