Inveed fir tree appearance on gelatin stab is characteristic of ?

Ans. is 'b' i.e., Bacillus anthracis Morphology ? . Gram positive . Non motile (all other members ofgenus Bacillus are motile) . Arranged singly, in pairs or in sho chains . Capsulated - entire chain being surrounded by a capsule. - Capsule is polypeptide . Sporing - Spores are formed in culture or in soil but never in animal body during life. . Chain of bacilli presents a bamboo stick appearance. Culture characteristics . On agar plates Frosted glass appearance . On gelatin stab culture --> Inveed fir tree appearance . Medusa head appearance - . String of pearl's reaction - Differentiates bacillus anthracis from B. cereus and other aerobic bacilli. . Cut glass appearance in transmitted light. . Non hemolytic . M' Fadyean's reaction When blood films containing anthrax bacilli are stained with polychrome methylene blue for a few seconds and examined under microscope, an amorphous purplish material is noticed around bacilli. This represents the capsular material and is characteristic of the anthrax bacillus. Remember . Selective media for B. antracis is PLET medium, consisting of polymyxin, lysozyme, ethylene diamine tetraacetic acid (EDTA) and thallous acetate added to hea infusion agar. . Ascoli's thermoprecipitin test is done for demonstration of anthrax antigen in tissue extract.