Bacterial Cell Wall Types Quiz

Gram Positive (G+) vs. Gram Negative (G-) Cell Walls

• G+ cell walls have a very thick peptidoglycan layer, teichoic acids, and lipoteichoic acids. Acid-fast cells also contain mycolic acid.
• Many G+ antibiotics target peptidoglycan synthesis.
• G- cell walls have a thin peptidoglycan layer and lack teichoic acids. Their outer membrane contains lipopolysaccharides (LPS), including Lipid A, which causes fever and shock in infections.

Bacterial Cell Wall Types

• Acid-fast cell walls: Found in Mycobacteria and Nocardia, they possess a G+ cell wall structure with a waxy layer of glycolipids and mycolic acids. This waxy layer makes them difficult to Gram stain; they are decolorized by acid-alcohol.
• Cell wall-less bacteria: Mycoplasma and Ureaplasma lack cell walls, resulting in varied microscopic shapes (spherical or disc-like).
• Some bacteria produce slime layers (loose gelatinous sheaths of polysaccharides) or capsules (thicker slime layers with nitrogen compounds). Capsules protect against phagocytosis and may appear as clear halos in staining.

Bacterial Cell Appendages

• Flagella: Exterior protein filaments enabling motility. Arrangements include monotrichous (single polar), lophotrichous (multiple at one pole), amphitrichous (single or multiple at both poles), and peritrichous (distributed around the cell).
• Pili (fimbriae): Hair-like projections aiding attachment to surfaces and acting as virulence factors (e.g., N. gonorrhoeae). They also participate in conjugation (DNA transfer).

Bacterial Genetic Material

• Bacteria possess a single, circular, double-stranded DNA molecule.
• They may also contain smaller, independently replicating extrachromosomal DNA molecules called plasmids, which often carry genes for antibiotic resistance or toxin production.

Bacterial Shapes and Arrangements

• Bacterial shapes include cocci (spherical), bacilli (rod-shaped), spirochetes (helical), and variations thereof.
• Arrangements include singly, in pairs (diplococci, diplobacilli), clusters (staphylococci), chains (streptococci, streptobacilli), palisades and fusiform.

Bacterial Size and Length

• Bacteria vary in size and length, described as short, long, filamentous, fusiform, curved, or pleomorphic.

Bacterial Staining

• The Gram stain is a differential stain classifying bacteria as Gram-positive (purple) or Gram-negative (red) based on cell wall structure.

Bacterial Internal Structures

• Ribosomes: Involved in protein synthesis.
• Cytoplasmic Inclusions: Serve as energy and nutrient reserves (organic, like glycogen, or inorganic, like sulfur or polyphosphate). Their size varies with environmental conditions.
• Endospores (Spores): Dormant, highly resistant cells formed by Bacillus and Clostridium species. They survive harsh conditions and can germinate under favorable conditions. Important in the epidemiology of diseases like anthrax, tetanus, and gas gangrene. Their eradication is crucial in sterilization processes (surgery, food canning).