**Question:** Anthrax bacilli differs from anthracoid bacilli by being:

A. Spore-forming
B. Non-spore-forming
C. Producing anthraquinone pigment
D. Present in soil

**Core Concept:**

Anthrax and anthracoid bacilli are two types of bacteria, where anthrax bacilli belong to the genus Bacillus, while anthracoid bacilli belong to the genus Anthracobacter. Anthrax bacilli are spore-forming, which means they have the ability to convert into a dormant form called spores, which helps them survive harsh conditions and enables them to cause anthrax disease in humans and animals. Anthracoid bacilli, on the other hand, are non-spore-forming, which makes them less virulent and not typically associated with disease in humans or animals.

**Why the Correct Answer is Right:**

The correct answer is B, "non-spore-forming." This is because anthrax bacilli are spore-forming bacteria, which is a distinctive feature of the anthrax bacilli that helps them survive harsh environmental conditions, ensuring the bacteria remain viable to cause anthrax disease. In contrast, anthracoid bacilli are non-spore-forming, which makes them less virulent and not commonly associated with disease in humans or animals.

**Why Each Wrong Option is Incorrect:**

A: Anthracoid bacilli are not spore-forming, but this information is correct for anthrax bacilli. The question asks for the difference between anthrax bacilli and anthracoid bacilli, not anthracoid bacilli and other bacteria.

C: Anthracoid bacilli produce anthraquinone pigment, which is not the distinguishing feature between anthrax bacilli and anthracoid bacilli.

D: Both anthrax bacilli and anthracoid bacilli can be found in soil. This option does not differentiate between the two types of bacilli, as the question focuses on their spore-forming or non-spore-forming nature.

**Clinical Pearl:** Anthrax infection is a serious illness caused by the spore-forming Bacillus anthracis, which is transmitted through contact with infected animals or contaminated products derived from them, such as wool, meat, or soil. Anthracoid bacilli, on the other hand, are non-pathogenic and do not cause anthrax or anthracoid disease. Understanding these differences helps differentiate between the two types of bacilli and their potential pathogenicity.