Shigella boydii: One of the SHIGELLA species that produces bacillary dysentery (DYSENTERY, BACILLARY).Shigella: A genus of gram-negative, facultatively anaerobic, rod-shaped bacteria that ferments sugar without gas production. Its organisms are intestinal pathogens of man and other primates and cause bacillary dysentery (DYSENTERY, BACILLARY).Shigella dysenteriae: A species of gram-negative, facultatively anaerobic, rod-shaped bacteria that is extremely pathogenic and causes severe dysentery. Infection with this organism often leads to ulceration of the intestinal epithelium.Dysentery, Bacillary: DYSENTERY caused by gram-negative rod-shaped enteric bacteria (ENTEROBACTERIACEAE), most often by the genus SHIGELLA. Shigella dysentery, Shigellosis, is classified into subgroups according to syndrome severity and the infectious species. Group A: SHIGELLA DYSENTERIAE (severest); Group B: SHIGELLA FLEXNERI; Group C: SHIGELLA BOYDII; and Group D: SHIGELLA SONNEI (mildest).Shigella sonnei: A lactose-fermenting bacterium causing dysentery.Shigella flexneri: A bacterium which is one of the etiologic agents of bacillary dysentery (DYSENTERY, BACILLARY) and sometimes of infantile gastroenteritis.Pseudallescheria: Ascomycetous fungi, family Microascaceae, order Microascales, commonly found in the soil. They are causative agents of mycetoma, maduromycosis, and other infections in humans.O Antigens: The lipopolysaccharide-protein somatic antigens, usually from gram-negative bacteria, important in the serological classification of enteric bacilli. The O-specific chains determine the specificity of the O antigens of a given serotype. O antigens are the immunodominant part of the lipopolysaccharide molecule in the intact bacterial cell. (From Singleton & Sainsbury, Dictionary of Microbiology and Molecular Biology, 2d ed)Hafnia alvei: The type species for the genus HAFNIA. It is distinguished from other biochemically similar bacteria by its lack of acid production on media containing sucrose. (From Bergey's Manual of Determinative Bacteriology, 9th ed)Serotyping: Process of determining and distinguishing species of bacteria or viruses based on antigens they share.Shigella Vaccines: Vaccines or candidate vaccines used to prevent bacillary dysentery (DYSENTERY, BACILLARY) caused by species of SHIGELLA.