Bacterial Structure; Gram staining Flashcards
Ziehl-Neelsen, Kinyoun, Auramine-Rhodamine, Pappenheim, Baumgarten, Wadefite, Gabett
Acid Fast
Neisser’s, Albert’s, Ljubinsky, LAMB (Loeffler’s Alkaline Methylene Blue), Burke’s
Metachromatic granules
Dyar, Victoria Blue, Calcofluor white (for Fungal chitin)
Cell wall
Levaditi Silver Impregnation, Fontana tribondeau
Spirochetes
Dorner’s, Wirtz-Conklin, Schaeffer-Fulton (primary stain is malachite green, mordant is green, decolorizer is tap water, 2nd stain - safranin; Green spore, Pink bacteria)
Endospore
Gray’s, Leifson, Caesares Gil, Fisher-Conn
Flagella
Anthony’s, Nigrosin, India Ink = negative stain
Capsule/Negative stains
Acridine orange, Feulgen
Nucleic acid/DNA
Gimenez, Macchiavello
Rickettsia
Dienes stain
Mycoplasma
McFadyean
Bacillus anthracis
Toluidine blue
Helicobacter pylori
Wayson’s
Bipolar bodies (Y. pestis)
Structure that includes the cell wall, plasma membrane, and other components defining the bacterial surface.
Cell Envelope
Bacterial classification basis
Cell wall is the primary basis of bacterial classification.
Peptidoglycan layer
Composed of N-acetyl-D-glucosamine (NAG) & N-acetyl-D-muramic acid (NAM).
Absence of outer membrane and periplasmic space; thick peptidoglycan; teichoic acid present; 2 basal rings for flagella; resistant to physical destruction.
Gram-positive
Presence of outer membrane and periplasmic space; thin peptidoglycan; lipopolysaccharide present; 4 basal rings for flagella; sensitive to physical destruction.
Gram-negative
Most important differential staining test in microbiology; stains the microorganism’s cell wall.
GRAM STAIN
Most critical step in Gram stain
Decolorization.
Primary stain used in Gram staining.
Crystal violet
Mordant used in Gram staining.
Gram iodine
Alcohol-acetone mixture used in Gram staining.
Decolorizer
Counterstain used in Gram staining.
Safrinin
Color after 2nd stain (Gram-positive)
Purple.
Color after 2nd stain (Gram-negative)
Pink.
Overdecolorization, old culture, acidic iodine, B-lactam drugs treatment
Gram-positive bacteria may appear Gram-negative.
Underdecolorization, too thick smear
Gram-negative bacteria may appear Gram-positive.
Direct smear
From specimen.
Indirect smear
From culture media.
Smear preparation steps
Smear → Air-dry → Fixation (10 mins. at 60°C or 1 min. in 95% methanol).
Direct smear reporting
Gram reaction, morphology, arrangement, and other elements seen.
QC Gram-positive
Staphylococcus aureus (purple to deep blue).
QC Gram-negative
Escherichia coli (pink to deep magenta).
Resists Decolorization
Acinetobacter, Kingella, Psychrobacter, Methylobacterium (may appear Gram-positive).
Gram Neutral/Ghost form
Bacillus anthracis (ghost capsule), Mycobacteria (poorly stained).
Poorly stained with Gram stain
Campylobacter, Brucella, Tropheryma whipplei.
Poorly stained with Safranin
Legionella, Gram-negative anaerobes, Francisella.
Not stained
Intracellular (Chlamydia, Rickettsia, Ehrlichia, Coxiella), No cell wall (Mycoplasma/Ureaplasma), Spirochetes (Dark-field microscopy).
Quantitating Organisms: None
No organism seen.
Quantitating Organisms: Rare
1+ <10 on complete smear.
Quantitating Organisms: Few
2+ 3–5 per OIF.
Quantitating Organisms: Moderate
3+ 6–10 per OIF.
Quantitating Organisms: Many
4+ >20 per OIF.
Quantitating Host cells: None
No host cells seen.
Quantitating Host cells: Rare
1+ <2 per LPF.
Quantitating Host cells: Few
2+ 2–10 per LPF.
Quantitating Host cells: Moderate
3+ 10–25 per LPF.
Quantitating Host cells: Many
4+ >25 per LPF.
Ghost forms
Cryptosporidium.
Ghost spherule
Coccidioides.
Q Score for Grading Clinical Sample
Used to evaluate sample quality based on neutrophil count and squamous epithelial cells.
Q Score 0
Average neutrophils: 0; no squamous epithelial cells.
Q Score +1
Average neutrophils: 1-9 (few); squamous epithelial cells: -1.
Q Score +2
Average neutrophils: 10-24 (moderate); squamous epithelial cells: -2.
Q Score +3
Average neutrophils: ≥25 (many/numerous); squamous epithelial cells: -3.
Interpretation of Q Score
Higher score indicates better quality of sample; a score of zero means the sample is superficial and not cultured.
Resists Decolorization
Acinetobacter, Kingella, Psychrobacter, Methylobacterium (may appear Gram-positive)
Appears as Gram Neutral/Ghost
Mycobacteria (Poorly stained)
Poorly stained with Gram stain
Campylobacter, Brucella, Tropheryma whipplei
Poorly stained with Safranin
Legionella, Gram-negative anaerobes, Francisella