Shigella dysenteriae is a bacterium of the Enterobacteriaceae family that is characterized in that it has a bacillus shape, is flagellate, is stained pink with Gram stain, does not form spores, nor does it produce gas when metabolizing carbohydrates.
This bacterium belongs to serogroup A of the genus Shigella. This genus is widely distributed worldwide, representing the main cause of bacterial or bacillary dysentery. In addition to serogroup A, there are three other main subgroups in this genus represented by the letters B to D (S. flexneri, S. boydii, and S. sonnei, respectively).

Dark-field microscopy revealing the bacterium Shigella dysenteriae. Taken and edited from: Armed Forces Institute of Pathology, AFIP.
Bacterial dysentery, also known as shigellosis, is an acute infection of the lining of the intestine that presents as diarrhea accompanied by fever, nausea or vomiting, colic and tenesmus, which mainly affects children under five years of age and the elderly, with high rates of morbidity and mortality worldwide.
References
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