Pathogens and Infection Process Quiz

Terminology

• Pathogen: A microorganism capable of causing disease in a host organism
• Primary pathogen: A microbe from the environment that can cause disease in a healthy individual
• Opportunistic pathogen: A member of the normal microbiota that causes disease only in immunocompromised individuals
• Pathogenicity: The ability of a pathogen to cause disease
• Virulence: The degree or intensity of pathogenicity
• Virulence factors: Mechanisms that determine the extent to which a pathogen causes damage, invasion, and infectivity

Process of Infection

• To survive, pathogens require:
  • A suitable environment
  • A source of nutrients
  • Protection from harmful elements

Bacterial Adhesins

• Adhesins: Virulence factors enabling pathogens to attach to host cells
• Specific Examples:
  • Streptococcus pyogenes (Strep throat): Protein F adheres to respiratory epithelial cells
  • Streptococcus mutans (Dental caries): Adhesin P1 attaches to teeth
  • Neisseria gonorrhoeae (Gonorrhoea): Type IV pili bind to urethral epithelial cells
  • Enterotoxigenic E. coli (ETEC) (Traveller's diarrhoea): Type 1 fimbriae attach to intestinal epithelial cells
  • Vibrio cholerae (Cholera): N-methylphenylalanine pili bind to intestinal epithelial cells

Capsules

• Some bacteria produce capsules that:
  • Aid in adhesion
  • Evasion of the immune system (preventing phagocytosis)
  • Capsule composition prevents antibody adhesion
  • Capsule size deters phagocytosis

Fimbriae and Cell Walls

• Fimbriae on some Streptococcus species contain M protein, altering the bacterial surface and hindering phagocytosis
• Mycolic acid, a waxy substance in the cell wall of Mycobacterium tuberculosis, acts as a protective coat deterring killing mechanisms during phagocytosis

Exoenzymes

• Extracellular enzymes secreted by cells that function outside of those cells
• Enable invasion of host cells and deeper tissues
• Breakdown specific tissue structures, supporting pathogen growth and defending against the immune system

Exoenzyme Examples

• Collagenases: Break down collagen, a major component of connective tissue
• Hyaluronidases: Break down hyaluronic acid, a component of extracellular matrix
• Proteases: Break down proteins, facilitating tissue invasion
• Coagulase: Catalyzes the conversion of fibrinogen to fibrin, forming a clot that protects the bacteria from the immune system
• Kinases: Dissolve fibrin clots, allowing bacteria to escape and spread
• DNases: Break down DNA, reducing the viscosity of mucus and facilitating bacterial spread

Toxins

• Biological poisons produced by pathogens that invade and damage tissues
• Toxigenicity: The ability of a pathogen to produce toxins to cause damage to host cells
• Types of Toxins:
  • Endotoxins: Lipopolysaccharide components of the outer membrane of gram-negative bacteria; stimulate a general systemic inflammatory response; stable at high temperatures; can cause severe inflammatory reactions and even death in high concentrations
  • Exotoxins: Potent protein molecules produced by a variety of bacteria (mainly gram-positive); highly specific in their action and target cells; inactivated by heat; low concentrations can be lethal; categorized into three groups based on their mode of action: intracellular targeting, membrane disrupting, superantigens

Terminology for Pathogens in the Bloodstream

• Bacteraemia: Presence of bacteria in the blood
• Pyaemia: Presence of pus-forming bacteria in the blood
• Toxaemia: Presence of toxins in the blood
• Septicaemia: Multiplying bacteria in the blood

Virulence Factors Promoting Infection

• Coagulase: Produced by Staphylococcus aureus, triggers fibrinogen conversion to fibrin, coating bacteria in clots and preventing phagocytosis
• Kinases: Digest fibrin clots, allowing bacteria to escape and spread
• Antigenic Variation: Surface proteins change to avoid recognition by the host's immune system, e.g., some viruses like influenza and HIV
• Leukocidins: Destroy phagocytes
• T Cell Destruction: Kill T lymphocytes
• Intracellular Position: Pathogens reside inside host cells, evading immune defenses

Viral Virulence

• Adhesins: Mediated by adhesions present in the viral capsid or membrane envelope; interact with specific cell receptors (tropism)
  • Example: Spike protein hemagglutinin on influenza virus; glycoprotein g20 on HIV
• Antigenic Variation:
  • Antigenic Drift: Minor changes in spike proteins due to point mutations
  • Antigenic Shift: Major changes in spike proteins resulting from gene re-assortment (major outbreaks)

Virulence Factors in Oral Health

• Porphyromonas Gingivalis: A primary pathogen in periodontal disease
  • Fimbriae: Modify and stimulate immune responses (cytokine secretion or inhibition)
  • Gingipains (proteases): Break down periodontal structural proteins like collagen, elastin & fibronectin
• Streptococcus Mutans: A major contributor to dental caries
  • Adhesion, acidogenicity, acid tolerance: These factors work together to alter the ecology of dental plaque, favoring the development of caries

Pathogen-Host Interactions

• Pathogens must evade immune defenses to survive and reproduce.
• Pathogens use strategies like antigenic variation to change their surface antigens, making it difficult for the immune system to recognize and attack them.
• Some pathogens can survive inside host cells, hiding from the immune system.

Successful Pathogens

• Successful pathogens exploit host resources while minimizing harm to the host.
• This allows the pathogen to survive long enough to reproduce and spread to new hosts.
• Pathogens that kill their host too quickly are less likely to be transmitted.

Test your knowledge on the terminology and processes related to pathogens and infection. This quiz covers primary pathogens, opportunistic pathogens, and virulence factors, providing a comprehensive understanding of how infections occur.