Bacterial Genetics and Virulence Factors

Bacterial Growth (2) - Bacterial Genetics and Virulence Factors

• Bacterial virulence factors are cellular structures, enzymes, and toxins that enhance bacterial pathogenicity.
• Key virulence factors include the capsule, fimbriae (pili), teichoic acid, enzymes, bacterial toxins (exotoxins/endotoxins), and pigments.

1- Bacterial Virulence

• Capsule: Resist phagocytosis and hydrolytic enzymes (lysozymes) that break down cell walls. Adheres to host cells.
• Fimbriae (Pili): Adheres to host cell surfaces.
• Teichoic Acid (Gram-positive bacteria): Adheres to host cell surfaces.

4- Microbial Enzymes

• Collagenase: Aids microbial invasion by degrading the extracellular matrix (collagen).
• Urease: Neutralizes acidic pH in urine and stomach.
• Hemolysin: Degrades red blood cells (RBCs) and releases hemoglobin.
• Haemagglutinin and coagulase enzyme: Agglutinates RBCs and coagulates plasma; the microbe can escape humoral immunity.
• Catalase: Breaks down hydrogen peroxide (H₂O₂) into water (H₂O) and oxygen (O₂).

5- Bacterial Toxins

• Exotoxins: Produced by Gram-positive and Gram-negative bacteria, diffuse outside the bacteria, are proteins, heat-labile, and toxoids formed for vaccine use.
• Endotoxins: Produced by Gram-negative bacteria, part of the cell wall, are lipopolysaccharides, heat-stable, have no effect from formalin treatment, and are less antigenic.
  • Examples: Clostridium botulinum toxin and Clostridium tetani toxin.

6- Bacterial Pigments

• Exopigments: Diffuse into the surrounding medium, an example is bluish-green pigments from Pseudomonas aeruginosa.
• Endopigments: Stay within the cell.

2- Bacterial Genetics

• Bacterial Chromosome: A single circular, double-stranded DNA.
• Plasmids: Additional genetic material outside the chromosome; circular, supercoiled DNA carrying important genes like those for resistance.

Mechanisms of Gene Transfer

• Conjugation: Transfer of plasmids from one bacterial cell to another via sex pili (in gram-negative bacteria).
• Transduction: Transfer of genetic material through a virus (bacteriophage).
• Transformation: Uptake of DNA fragments from a lysed donor bacterial cell by a recipient cell.

Additional Information

• Corynebacterium diphtheriae: This bacterium causes diphtheria and produces diphtheria toxin. The gene encoding the toxin is transferred to other bacteria via a bacteriophage (transduction).