02. Bacterial Constituents 1

E. coli

Gram Stain / Morphology: Gram-negative rod (1×3 micrometers)

Key Virulence / Structural Factor:LPS (Endotoxin) in outer membrane

Diagnostic / Identification:Gram stain (Red/Pink)

Treatment Highlight: Beta-lactams (targets wall)

S. pneumoniae

Gram Stain / Morphology: Gram-positive cocci (chains/pairs)

Key Virulence / Structural Factor: Polysaccharide Capsule (Facultative)

Diagnostic / Identification: Gram stain (Purple/Blue)

Treatment Highlight: Penicillin (targets transpeptidase)

Caulobacter crescentus

Gram Stain / Morphology:Gram-negative (curved)

Key Virulence / Structural Factor:Crescentin (maintains shape)

Diagnostic / Identification: Microscopy (Crescent shape)

Treatment Highlight: N/A (Freshwater bacterium)

Mycoplasma spp.

Gram Stain / Morphology: No Cell Wall

Key Virulence / Structural Factor: Cholesterol in cytoplasmic membrane

Diagnostic / Identification: Does not Gram stain

Treatment Highlight: Resistant to Penicillin

H. influenzae

Gram Stain / Morphology: Gram-negative coccobacillus

Key Virulence / Structural Factor: LPS and Capsule (some types)

Diagnostic / Identification: Gram stain (Red/Pink)

Treatment Highlight: Cephalosporins (cell wall target)

What are the four obligate constituents of a bacterial cell?

1. Cytoplasmic membrane

2. Cytoplasm

3. Chromatin

4. Cell wall

How do Gram-positive and Gram-negative cell walls differ in peptidoglycan thickness?

Gram-positive bacteria have many thick layers of peptidoglycan

Gram-negative bacteria have a very thin peptidoglycan layer located in the periplasmic space

What is the clinical significance of Lipid A?

Toxic component of Lipopolysaccharide (LPS/Endotoxin) in Gram-negative bacteria.

It can trigger fatal endotoxin shock.

What specific enzyme does Penicillin bind to in order to inhibit cell wall synthesis?

It binds to transpeptidase, the enzyme responsible for cross-linking peptidoglycan.

How does Vancomycin differ from Penicillin in its mechanism of action?

Instead of binding to an enzyme, Vancomycin binds directly to the peptide fragments of the peptidoglycan structure to prevent assembly.

Which bacterium is the exception to the rule that prokaryotes lack cholesterol?

Mycoplasma spp., which contains a multilayered cholesterol-containing membrane and lacks a cell wall.

What is the function of the FtsZ protein?

It is a tubulin-like protein that assembles into a ring at the future site of the septum during bacterial cell division.

What are the subunits of a prokaryotic ribosome, and why are they important?

50S and 30S (total 70S); they are important because they are primary targets for antibiotics.