Inveed fir tree appearance on gelatin stab is characteristic of?: (A) Mycoplasma, (B) Bacillus anthracis, (C) Clostridium, (D) Bacteriodes
Answer is B. Virulent capsulated strains of Bacillus anthracis form rough culture, while avirulent or attenuated strains form smooth colonies. on gelatin stab culture, a characteristic 'inveed fir tree' appearance is seen with slow liquefaction commencing from the top. On blood agar the colonies are nonhemolytic though occasional strains produce a narrow zone of hemolysis .in broth growth occurs as floccular deposits with little or no turbidity REF:Ananthanarayan & Panicker's Textbook of Microbiology 8th Edition pg no: 243