Some bacteria produce characteristic pigments that aid in identification. These pigments can also have clinical significance (eg, reactive oxygen species production, tissue staining).
Actinomyces israelii
- Produces yellow “sulfur granules” (actually composed of bacterial filaments).
- Mnemonic: “Israel has yellow sand.”
Staphylococcus aureus
- Produces golden-yellow pigment.
- Name reminder: “Aureus” = gold (Latin).
Pseudomonas aeruginosa
- Produces blue-green pigments (pyocyanin and pyoverdin).
- Mnemonic: “Aerugula is green.”
- Clinical note: Pyocyanin generates ROS, contributing to tissue damage.
Serratia marcescens
- Produces red pigment.
- Mnemonic: “Red Sriracha hot sauce.”
Summary Table: Pigment-Producing Bacteria
| Organism | Pigment | Mnemonic / Association |
|---|---|---|
| Actinomyces israelii | Yellow “sulfur” granules | “Israel has yellow sand” |
| Staphylococcus aureus | Golden-yellow | “Aureus = gold” |
| Pseudomonas aeruginosa | Blue-green (pyocyanin, pyoverdin) | “Aerugula is green” + ROS damage |
| Serratia marcescens | Red | “Red Sriracha hot sauce” |
Learning Objective (USMLE Step 1): Recognize pigment-producing bacteria and associate each organism with its characteristic color, which is frequently tested as an identification clue in microbiology questions.
Activity: Identify these bacteria based on the pigments.
