Microbiology: Pathogens and Infection

Pathogens and Microorganisms

• A pathogen is a microorganism that can cause disease.
• Types of microorganisms:
  • Saprophytic: live freely in nature.
  • Parasitic: live in/on a living host.
  • Pathogenic: cause disease.
  • Commensal: live in/on a living host without causing disease.
  • Opportunistic: commensals that can cause disease under certain conditions.

Bacterial Carrier

• A carrier is a healthy individual who possesses microorganisms and can transmit them.
• Types of carriers:
  • Transient: possess microorganisms for a short period (incubation period).
  • Permanent: possess microorganisms for a long period (chronic).
• Carriers are serious because they can communicate normally and carry the organism throughout the entire epidemic period.

Infection and Disease

• Infection: the relationship between a microorganism and a host.
• Disease: the destruction of host tissue by microorganisms due to:
  • Invasion of tissue.
  • Toxin production.
  • Other virulence factors.

Factors that Govern Disease Production

• Microbial factors:
  • Virulence: the degree of pathogenicity, determined by genes.
  • Pathogenicity: the ability to cause disease.
• Host resistance factors:
  • Natural immunity.
  • Acquired immunity.

Virulence Factors of Bacteria

• Invasive factors:
  • Adherence factors (pili, fimbriae, glycocalyx).
  • Ability to invade tissues, multiply, and spread rapidly.
• Toxin production:
  • Exotoxins: protein toxins produced by living bacteria, acting on specific cells.
  • Endotoxins: lipopolysaccharide toxins produced by dead bacteria, causing a general effect.

Exotoxins and Endotoxins

• Exotoxins:
  • Produced by living bacteria.
  • Act on specific cells.
  • Can be controlled by genes on plasmids and bacteriophage.
  • Examples: diphtheria toxin, cholera toxin, tetanus toxin.
• Endotoxins:
  • Produced by dead bacteria.
  • Cause a general effect (endotoxic or septic shock).
  • Can be controlled by genes on chromosomes.
  • Examples: Gram-negative bacteria.

Properties of Exotoxins and Endotoxins

• Exotoxins:
  • Location of genes: plasmid, bacteriophage, PAIs.
  • Composition: proteins.
  • Action: specific.
  • Heat stability: labile, destroyed at 60°C.
  • Diffusibility: diffusible.
  • Immunogenicity: strong.
  • Toxicity: strong.
  • Convertibility to toxoid: yes.
• Endotoxins:
  • Location of genes: bacterial chromosome.
  • Composition: lipopolysaccharide.
  • Action: non-specific.
  • Heat stability: stable at 100°C for 1 hour.
  • Diffusibility: not diffusible.
  • Immunogenicity: weak.
  • Toxicity: weak.
  • Convertibility to toxoid: no.

This quiz covers the basics of microbiology, including types of pathogens, bacterial carriers, infection, and disease. It also explores factors that contribute to disease production and bacterial pathogenicity.