All are catalase positive Except: (A) Shigella flexineri, (B) Shigella boydii, (C) Shigella dysentriae type I, (D) Shigella sonnei
Answer is C. S.dysenteriae (subgroup A): This species of mannitol non-fermenting bacilli consists of ten serotypes. It is indole negative and is the only member of the family that is always catalase-negative. S.flexineri, S.boydii, and S.sonnei are catalase positive. Ref: Textbook of microbiology; Aanthanarayan and paniker's; 10th Edition; Pg:292