Bacillus anthracis (Anthrax)

00:00 / 00:00



Bacillus anthracis (Anthrax)


Introduction to bacteria

Bacterial structure and functions


Bacillus anthracis (Anthrax)


0 / 16 complete

USMLE® Step 1 questions

0 / 2 complete

High Yield Notes

6 pages


Bacillus anthracis (Anthrax)

of complete


USMLE® Step 1 style questions USMLE

of complete

A 30-year-old man presents to the emergency department due to severe shortness of breath and a cough with blood in the sputum. The patient started feeling tired and having myalgias a few days ago. The shortness of breath began yesterday and has worsened ever since. The patient does not smoke or drink alcohol, and is employed on a horse farm. Chest X-ray demonstrates pulmonary infiltrates and a widened mediastinum. Sputum culture reveals a Gram-positive bacterium with a polypeptide capsule. Which of the following organisms is the most likely cause of this patient’s condition?  

External References

First Aid








Anthrax toxin

Bacillus anthracis and p. 135

Bacillus anthracis p. , 135

capsule composition p. 121

exotoxin production p. 130

spore formation p. 129


With Bacillus anthracis, bacillus means little rod and anthracis means coal.

So Bacillus anthracis is a rod-shaped bacteria that causes a disease called anthrax, that’s associated with characteristic black skin lesions.

Throughout history, Bacillus anthracis, or B. anthracis for short, has caused a number of plagues in Europe, and it’s also been used as biological warfare.

Not a good reputation!

Ok, now B. Anthracis has a thick peptidoglycan cell wall, which takes in purple dye when Gram stained - so this is a gram-positive bacteria.

Also, it is a non-motile bacteria and a facultative anaerobe, meaning it can survive with or without oxygen.

B. Anthracis is also a non beta-hemolytic bacteria, because when cultivated on a medium called blood agar, B. Anthracis colonies don’t cause beta-hemolysis, where hemolysis, or breakdown of the red blood cells that surround the colonies makes the blood agar change color from red to transparent yellow.

Finally, Bacillus Anthracis is a spore-forming bacteria, so it can undergo endosporulation when it feels threatened by the environment, like when the temperature becomes too high or too low, in case of extreme dryness, or when there’s harmful radiation around.

Endosporulation means that the bacteria starts by replicating its DNA, and then it forms a wall inside the cell, isolating the big portion of the cell, let’s call it the mother cell, from the small portion of the cell.

Next, the plasma membrane of the cell surrounds the newly formed small portion and then pinches it off, forming a separate body known as a forespore.

Next, the forespore gets completely engulfed by the mother cell, something like a cell within a cell.

Finally, inside the dying mother cell, the forespore loses water and accumulates calcium, and at the same time gets wrapped in a super tough cortex from the dying mother cell.

At this point, the endospore is able to resist heat, due to the presence of dipicolinic acid found in the core of the Bacillus anthracis spore, harsh chemicals, digestive enzymes, and even antibiotics.


Bacillus anthracis is an encapsulated, spore-forming, gram-positive bacteria bacterium that's known to cause anthrax. Anthrax can cause severe pulmonary, gastrointestinal, or cutaneous illnesses in humans. Anthrax can be transmitted via ingestion, inhalation, and skin invasion by the bacteria or its spores, often via direct interaction with infected animals.

It is more seen in agricultural regions where livestock are infected with the bacteria. Depending on the affected organs, it can present with a black necrotic skin lesion; fever, respiratory distress, abdominal pain, septic shock, and death if bloodstream infection occurs.


Copyright © 2023 Elsevier, its licensors, and contributors. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

Cookies are used by this site.

USMLE® is a joint program of the Federation of State Medical Boards (FSMB) and the National Board of Medical Examiners (NBME). COMLEX-USA® is a registered trademark of The National Board of Osteopathic Medical Examiners, Inc. NCLEX-RN® is a registered trademark of the National Council of State Boards of Nursing, Inc. Test names and other trademarks are the property of the respective trademark holders. None of the trademark holders are endorsed by nor affiliated with Osmosis or this website.