Final answer:
Streptococcus pyogenes is the most common causative organism of peritonsillar abscess, known for its pus-producing properties.
Step-by-step explanation:
The most common causative organism of a peritonsillar abscess is Streptococcus pyogenes, which is option (1) in the question provided. Streptococcus pyogenes is a gram-positive bacterium belonging to the Lancefield group A streptococci, often referred to as GAS or group A strep. It is recognized as a pyogenic pathogen due to the pus production associated with the infections it causes, such as strep throat and various skin infections including impetigo and necrotizing fasciitis.