**Core Concept**
Legionella is a genus of Gram-negative, aerobic bacteria that cause Legionnaires' disease, a severe form of pneumonia. Legionella species are typically found in aquatic environments, such as water systems, and require specific nutrients for growth.

**Why the Correct Answer is Right**
Legionella are not typically transmitted from person-to-person, unlike many other infectious agents. The primary mode of transmission is through inhalation of aerosolized water droplets contaminated with Legionella bacteria. Person-to-person transmission of Legionella is extremely rare and has not been well-documented in medical literature. This is due to the fact that Legionella bacteria do not survive for extended periods outside of their aquatic environment and are not typically present in high enough concentrations in respiratory secretions to pose a risk of transmission.

**Why Each Wrong Option is Incorrect**
**Option A:** Legionella can be grown on complex media such as buffered charcoal yeast extract agar (BCYE), which provides the necessary nutrients for growth. This is a key characteristic of Legionella species.
**Option B:** L. pneumophila serogroup 1 is indeed the most common serogroup isolated from humans, accounting for the majority of Legionnaires' disease cases.
**Option D:** L. pneumophila is not effectively killed by polymorphonuclear leukocytes (PMNs), which are a type of white blood cell that plays a key role in the innate immune response. The ability of L. pneumophila to evade PMN killing is one of the factors that contributes to its virulence.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that Legionnaires' disease is often misdiagnosed as community-acquired pneumonia, particularly in the early stages of the illness. Clinical suspicion should be high in patients with a history of travel, exposure to contaminated water systems, or underlying immunocompromised states.

**✓ Correct Answer:** C. Legionella are communicable from infected patients to others