Which of the following is an intracellular parasite?
a. Rickettsia
b. Mycobacterium
c. Bacillus
d. Staphylococcus
e. Streptococcus

Verified step by step guidance

Step 1: Understand the term 'intracellular parasite' — it refers to an organism that must live and reproduce inside the cells of a host to survive.

Step 2: Review the characteristics of each option: Rickettsia, Mycobacterium, Bacillus, Staphylococcus, and Streptococcus.

Step 3: Recall that Rickettsia species are known to be obligate intracellular parasites, meaning they cannot reproduce outside host cells.

Step 4: Recognize that Mycobacterium, Bacillus, Staphylococcus, and Streptococcus are generally free-living or extracellular bacteria and do not require living inside host cells to survive.

Step 5: Conclude that among the given options, Rickettsia is the intracellular parasite.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Intracellular Parasites

Intracellular parasites are organisms that must live and reproduce inside the cells of a host. They rely on the host's cellular machinery for survival and cannot complete their life cycle outside host cells. This lifestyle often helps them evade the host's immune system.

Rickettsia Characteristics

Rickettsia is a genus of small, Gram-negative bacteria that are obligate intracellular parasites. They infect host cells, typically endothelial cells, and are transmitted by arthropod vectors like ticks. Their intracellular nature distinguishes them from many other bacteria.

Differences Between Bacterial Genera

Mycobacterium, Bacillus, Staphylococcus, and Streptococcus are generally free-living or extracellular bacteria. Mycobacterium includes species causing tuberculosis, Bacillus includes spore-formers, while Staphylococcus and Streptococcus are common skin and respiratory tract bacteria, none of which are obligate intracellular parasites.

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