Evaluation of the impact of Shigella virulence genes on the basis of clinical features observed in patients with shigellosis

Shigella is still attributable to nearly 164,300 deaths annually, mostly in sub-Saharan Africa and South Asian young children, remaining as a major public health threat, especially in the developing countries. Our goal was to study the association between Shigella virulence genes and clinical features observed in shigellosis. Therefore, 61 S. flexneri strains were investigated, isolated from patients from a tertiary level facility in Bangladesh between 2009 to 2013. Subsequently, the presence of 140 MDa large virulence plasmid (p140), virulence (ipaH, ial), toxin (set, sen) and T3SS related genes (virB, ipaBCD, ipgC, ipgB1, ipgA, icsB, ipgD, ipgE, ipgF, mxiH, mxiI, mxiK, mxiE, mxiC, spa15, spa47, spa32 and spa24) were evaluated. p140 was found in 79% (n=48) cases. ipaBCD was found in 90% (n=55) strains, while seven of them were missing p140. However, ial was found in 89% isolates, and ipgC and ipgE in 85% cases. The prevalence of the rest of the genes was less than 85%. These findings were then compared against the clinical features of each of the corresponding pathogens, and several statistically significant correlations were observed (all p<0.05). Briefly, the enterotoxin genes (set, sen) and another virulence gene (ial) were found significantly associated with several clinical features of shigellosis, including bloody mucoid stool, rectal straining, fever, and abdominal pain. Our findings reiterate that the diarrheal disease severity is significantly associated with the enterotoxin producing Shigella infection, also suggesting that the T3SS related virulence genes might be translocated elsewhere other than the 140 MDa large virulence plasmid.