Gram Stain Chart

37 organisms. Stain + morphology = pattern. Pattern = treatment decision.

Opening Pattern

36-hour-old neonate. Fever, poor feeding, bulging fontanelle. Blood culture grows gram-positive cocci in chains. Beta-hemolytic on blood agar. Bacitracin-resistant. CAMP test positive. What do you give, and why not ceftriaxone?

CAMP test positive locks in GBS (S. agalactiae). The treatment is ampicillin + gentamicin, not ceftriaxone. Why not cephalosporins? Neonatal meningitis empiric coverage must include Listeria monocytogenes, and every cephalosporin misses it. Ampicillin covers both GBS and Listeria. Gentamicin provides aminoglycoside synergy for bactericidal effect. That gap in cephalosporin coverage is a clinical medicine pattern you have to know cold.

How the Gram Stain Works

Tap each step. Watch what happens to the cell wall.

STEP 1 OF 4

Crystal Violet

Purple dye floods every cell regardless of wall thickness. At this point everything looks purple. No discrimination yet between gram-positive and gram-negative.

Organism	Stain	Morphology	Key Virulence	Clinical	First-Line Tx

Pattern Recognition 6 clinical vignettes

Stain result + clinical picture. What organism, what treatment, and why?

Board Walkthrough

25 original clinical vignettes. One at a time. Shuffle resets when you exhaust the bank.

← Continue studying Microbiology

Medically reviewed by Kaitlyn Cocuzzo, MD and Fatima Ali, DO · Last updated June 30, 2026 at 2:05 AM ET

Bone Wizardry is an independent educational resource for visual learning in the medical sciences. It is not affiliated with, endorsed by, or sponsored by any licensing or examination board, contains no real or recalled examination questions, and does not guarantee any educational or examination outcome.