32 year old man, presented with painless ulcer with a black eschar on his leg. Smears of exudate show non motile organisms which are in chains. Spores are absent in the smear. Most probable organism is:
Bacillus anthracis is a large gram-positive rod with square ends, frequently found in chains. It is non motile, whereas other members of the genus are motile. Spores are usually not seen in smears of exudate because spores form when nutrients are insufficient, and nutrients are plentiful in infected tissue. Also know: Anthrax toxin is encoded on one plasmid, and the polyglutamate capsule is encoded on a different plasmid. Its antiphagocytic capsule is composed of D-glutamate. (This is unique--capsules of other bacteria are polysaccharides.) Ref: (2012). Chapter 17. Gram-Positive Rods. In Levinson W (Eds), Review of Medical Microbiology & Immunology, 12e.
Proteus
Diphtheroids
Clostridium
Bacillus anthracis