03. Bacterial Constituents 2

Bacillus anthracis

Gram Stain / Morphology: Gram-positive rod

Key Virulence Factor(s): Unique peptide capsule (antiphagocytic)

Gold Standard Diagnostic / ID: Capsule observation (negative staining)

Clostridium tetani

Gram Stain / Morphology: Gram-positive rod

Key Virulence Factor(s): Endospore (highly resistant, survival factor)

Gold Standard Diagnostic / ID: Endospore staining / clinical symptoms

Klebsiella

Gram Stain / Morphology: Gram-negative rod

Key Virulence Factor(s): Type 1 Fimbria (adhesin)

Gold Standard Diagnostic / ID: Yeast cell co-agglutination (phenotyping)

Bacillus cereus

Gram Stain / Morphology: Gram-positive rod

Key Virulence Factor(s): Endospore formation

Gold Standard Diagnostic / ID: Dorner endospore staining method

B. stearothermophilus

Gram Stain / Morphology: Gram-positive rod

Key Virulence Factor(s): Heat-resistant endospores

Gold Standard Diagnostic / ID: Used to test autoclave efficiency (121°C)

Capsule

Antiphagocytic effect

Target for vaccines (K-antigen)

LPS (Lipid A)

Endotoxin (Gram-negatives)

Found in the outer membrane of Gram-negatives.

Flagellum

Active motility (rotation)

Carries the H-antigen.

Sex-Pilus

Conjugation

Facilitates DNA transfer between bacteria.

Fimbriae

Adhesion to host cells

Specifically binds to host cell receptors.

Endospore

Survival (not multiplication)

Killed only by autoclaving (121°C, 15 mins).

List the four primary obligate constituents of a bacterial cell.​

​Cytoplasmic membrane

​Cytoplasm

​Chromatin

​Cell wall (envelope)

What is the fundamental difference between Gram-positive and Gram-negative peptidoglycan layers?

Gram-positive bacteria have 20–100 layers of peptidoglycan, while Gram-negative bacteria only have 1–2 layers.

What unique components are found in the Gram-negative outer membrane?

Lipopolysaccharide (LPS), specifically Lipid A

​Porins (for transport and as receptors)

​Periplasmic space

What is the primary virulence factor in the cell wall of Gram-positive bacteria?

Teichoic acid and Lipoteichoic acid.

What are the four steps of the Gram staining procedure in order?

1. Primary Stain: Crystal violet

2. Mordant: Gram’s Iodine (Lugol solution)

3. Decolorization: Acetone-alcohol

4. Counterstain: Safranin

What clinical error results in a "False Gram-negative" result?

Over-decolorization (over-differentiation) with acetone-alcohol, which causes Gram-positive cells to lose their violet color.

What is the primary function and pathogenicity role of a bacterial capsule?

Function: Pathogenicity factor with an antiphagocytic effect.

​Clinical Significance: Acts as a vaccine target (K-antigen) and aids in biofilm formation (e.g., dental plaque, catheters).

Which bacterium is an exception to the rule that capsules are made of carbohydrates?

B. anthracis, which has a peptide capsule.

What is the motility organ of bacteria and what antigen does it carry?

The Flagellum, which moves via rotation and carries the H-antigen.

Define the difference between Fimbriae and Sex-Pili.

Fimbriae (Adhesins): Specifically bind to host cell receptors for colonization.

​Sex-Pilus: Facilitates conjugation (the transfer of DNA from a donor to a recipient).

Does endospore formation serve the purpose of multiplication?

No. It serves the survival of the bacteria in harsh conditions, not reproduction.

What are the specific autoclave requirements to inactivate (kill) bacterial endospores?

121°C (249.8°F) + 1 atm of pressure for 15 minutes.

Name three bacteria mentioned in the slides that form endospores.

1. Clostridium tetani

2. Bacillus stearothermophilus

3. Bacillus cereus

What staining method is used specifically for B. cereus endospores?

The Dorner endospore staining method