**Core Concept**
Viridans streptococci are a group of Gram-positive cocci that belong to the genus Streptococcus. They are commonly found in the oral cavity and are known to cause infections, particularly infective endocarditis, especially in individuals with pre-existing heart conditions.

**Why the Correct Answer is Right**
The correct answer, B. ADE is true, indicates that all the options A, D, and E are correct statements regarding viridans streptococci. **Option A** is correct because it includes Streptococcus mutans, mitis, sanguis, and salivarius, which are all types of viridans streptococci. **Option D** is correct as it refers to the cariogenic strains of viridans streptococci, which are known to contribute to tooth decay. **Option E** is correct because viridans streptococci can be isolated from the bloodstream in the majority of patients immediately after dental extraction, highlighting their ability to translocate from the oral cavity to the bloodstream.

**Why Each Wrong Option is Incorrect**
**Option B** is incorrect because while viridans streptococci can produce haemolysis on blood agar plates, it is not a reliable method for their identification. **Option C** is incorrect as viridans streptococci are a common cause of infective endocarditis, particularly in individuals with pre-existing heart conditions.

**Clinical Pearl / High-Yield Fact**
Viridans streptococci are often considered "commensal" organisms, meaning they can exist in the oral cavity without causing harm. However, their ability to translocate to the bloodstream and cause infections, such as infective endocarditis, makes them a significant concern, especially in patients with pre-existing heart conditions.

**✓ Correct Answer: B. ADE is true**