**Question:** HACEK group of organisms includes all of the following, EXCEPT:

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

**Core Concept:** The HACEK group refers to a group of gram-negative, aerobic, coccobacillary bacteria that can cause various infections in humans, particularly in the cardiovascular system. The acronym HACEK represents the key organisms involved: Haemophilus, Actinomyces, Cardiobacterium, Eikenella, and Kingella.

**Why the Correct Answer is Right:** Haemophilus influenzae is a non-HACEK organism that is typically associated with respiratory tract infections and meningitis, not cardiovascular infections.

**Why Each Wrong Option is Incorrect:**

A. Haemophilus influenzae: As stated above, this organism is associated with respiratory tract infections and meningitis, not cardiovascular infections.
B. Actinomyces israelii is a member of the Actinomyces genus, which is not part of the HACEK group. Actinomyces israelii is commonly found in the oral cavity and gastrointestinal tract, often associated with dental abscesses and sinusitis.
C. Cardiobacterium hominis is another member of the HACEK group, so this option is incorrect as it belongs to the group.
D. Eikenella corrodens is also a member of the HACEK group and is known to cause bacteremia and endocarditis.

**Clinical Pearl:** The HACEK group is a crucial group to know for medical students and practitioners, as awareness of these organisms can help guide diagnosis and treatment of infections caused by them, particularly in patients with underlying heart conditions (e.g., prosthetic valves, rheumatic heart disease).

**Correct Answer:** D. Eikenella corrodens. This bacterium is part of the HACEK group and is known to cause bacteremia and endocarditis, making it the correct answer to exclude.