**Question:** HACEK group includes all of the following except

A. Haemophilus influenzae
B. Actinomyces species
C. Cardiobacterium hominis
D. Eikenella corrodens

**Correct Answer:** .

**Core Concept:** HACEK group is a collection of gram-negative, facultatively anaerobic bacteria that are known to cause infective endocarditis. The acronym HACEK represents the first letter of each bacteria species:

1. Haemophilus influenzae: This bacterium is typically found in the respiratory tract and is not typically associated with infective endocarditis.
2. Actinomyces species: These bacteria are part of the normal oral flora and are not commonly associated with infective endocarditis.
3. Cardiobacterium hominis: This bacterium is also part of the normal oral flora and is not a common cause of infective endocarditis.
4. Eikenella corrodens: Although this bacterium is known to cause infective endocarditis, it is less common than the other HACEK bacteria.

**Why the Correct Answer is Right:** Option A (Haemophilus influenzae) is not part of the HACEK group as it is not primarily associated with infective endocarditis. Haemophilus influenzae is more commonly associated with respiratory tract infections.

**Why Each Wrong Option is Incorrect:**

Option B (Actinomyces species) is incorrect because Actinomyces are part of the normal oral flora and are not a primary cause of infective endocarditis.

Option C (Cardiobacterium hominis) is incorrect because this bacterium is also part of the normal oral flora and is less commonly associated with infective endocarditis compared to other HACEK bacteria.

Option D (Eikenella corrodens) is incorrect because although Eikenella corrodens can cause infective endocarditis, it is less common than other HACEK bacteria like Haemophilus azoospermicus and Agrobacterium ureae.

**Clinical Pearl:** Infective endocarditis is a severe infection of the heart valves, and the HACEK group of bacteria is known to cause this condition in susceptible patients, particularly those with underlying heart diseases or prosthetic heart valves. It is essential for healthcare professionals, especially cardiologists, to be familiar with these bacteria as prompt diagnosis and treatment can prevent complications and improve patient outcomes.