<prompt> Which is the largest pathogenic bacillus ?Bacillus cereusBacillus subtilisBacillus megateriumBacillius anthracis  <response>: Ans: D Bacillius anthracis Ref: Ananthnarayan R. Paniker CKJ. Textbook of Microbiology. 8th Edition. Hyderabad: Universities Press; 2009. Pg. 242Explanation:Bacillus anthracisConsiderable historical interest is attached to the anthrax bacillus.First pathogenic bacterium to be observed under the microscopeFirst communicable disease shown to be transmitted by inoculation of infected bloodFirst bacillus to be isolated in pure culture and shown to possess sporesFirst bacterium used for the preparation of an attenuated vaccineThe anthrax bacillus is the largest of pathogenic bacteria, measuring 3-10 mm x 1-1.6 mm.Characteristics of Bacillus anthracisBamboo stick appearancePolypeptide capsule - MFadyeans reaction stain with Polychrome Methylene blueEdge of colony under dissecting Microscope shows Medusa Head appearanceNutrient agar -Frosted glass appearanceBlood Agar - No or Minimal HemolysisSelective Medium - PLETmedium Polymyxin, Lysozyme, EDTA, thallous acetateGelatin Stab Culture - Inverted Fir Tree appearanceString of Pearls - media with .05 - .5 U PenG ml 