Streptococcus: Overview and Classification

j16r-2026-01-28_06_29_20-strep.pdf

Hello! I'm ready to dive into the world of Streptococcus with you. This genus is a cornerstone of medical microbiology, responsible for everything from a simple sore throat to life-threatening heart disease.

To understand these bacteria, we don't just memorize names; we look at how they behave on a blood agar plate and what "tags" they carry on their surfaces.

One. The Big Picture: What is Streptococcus?

First, let's place them in the bacterial family tree. As you know from your notes, all cocci (round bacteria) are Gram-positive except for the "VeNoM" group (Neisseria, Veillonella, Moraxella).

Streptococci are:

· Gram-positive cocci.

· Arrangement: They grow in chains.

· Analogy: Think of Staphylococcus as a "bunch of grapes," while Streptococcus is a "string of pearls."

· Catalase Test: This is the most important first step in the lab. Streptococci are Catalase-negative.

· The Reasoning: Unlike Staphylococci, Streptococci lack the enzyme catalase to break down hydrogen peroxide (H two O two) into water and oxygen. If you drop H two O two on them, you won't see any bubbles.