Comparative genome analysis of 12 Shigella sonnei strains: virulence, resistance, and their interactions.

Shigellosis is a highly infectious disease that is mainly transmitted via fecal-oral contact of the bacteria Shigella. Four species have been identified in Shigella genus, among which Shigella flexneri is used to be the most prevalent species globally and commonly isolated from developing countries. However, it is being replaced by Shigella sonnei that is currently the main causative agent for dysentery pandemic in many emerging industrialized countries such as Asia and the Middle East. For a better understanding of S. sonnei virulence and antibiotic resistance, we sequenced 12 clinical S. sonnei strains with varied antibiotic-resistance profiles collected from four cities in Jiangsu Province, China. Phylogenomic analysis clustered antibiotic-sensitive and resistant S. sonnei into two distinct groups while pan-genome analysis reveals the presence and absence of unique genes in each group. Screening of 31 classes of virulence factors found out that type 2 secretion system is doubled in resistant strains. Further principle component analysis based on the interactions between virulence and resistance indicated that abundant virulence factors are associated with higher levels of antibiotic resistance. The result present here is based on statistical analysis of a small sample size and serves basically as a guidance for further experimental and theoretical studies.