Microbial Mechanisms of Pathogenicity Quiz

Microbial Mechanisms of Pathogenicity

• Pathogen: A microorganism that causes disease in a host.
• Infection: When a pathogen successfully colonizes a host.
• Infectious Disease: Disease caused by a pathogen.
• Communicable Disease: Spread from person to person.
• Noncommunicable Disease: Not spread from person to person.
  • Examples of Noncommunicable Disease Transmission: Tetanus (skin wound), Legionnaires (breathing contaminated water).

Stages of Pathogensis

• Exposure (contact): Encounter with a potential pathogen (food, objects, etc.). Exposure does not always lead to infection. To cause infection, a pathogen must pass through a portal of entry (skin, mucous membranes, parenteral route).
• Adhesion: Pathogens attach to host cells via adhesion factors (e.g., pili, glycoproteins).
• Invasion/colonization: Pathogens invade host tissues. This is aided by exoenzymes and toxins that allow for colonization, damage, and spreading.
  • Intracellular Pathogens: Get inside of cells, use host nutrients, and evade immune system.
  • Examples of Invasion by H. pylori: The bacterium produces urease, which neutralizes stomach acid, allowing it to penetrate the stomach lining.
• Infection: The pathogen multiplies after its successful invasion. Infection can be local, focal, or systemic.

Infection: Local, Focal, and Systemic

• Local: Infection localized to the site of entry (boil around hair follicle, UTI in bladder, pneumonia in lungs).
• Focal: Infection spreads from the site of entry to a secondary location (cut in gums, spreading through blood).
• Systemic: Infection spreads throughout the body (Varicella Zoster through mucous membrane, upper respiratory tract and results in a rash).

Secondary Infections

• Opportunistic Pathogens: Pathogens that only cause disease in immunocompromised hosts.
  • Examples of conditions impacting hosts: breaks in skin (wounds/burns), lowered immune system (AIDS), issues with normal microbiome, being young or old, pregnant, undergoing chemotherapy, recovering from surgery.
• Normal Microbiota: Can become opportunistic if the balance of the microbiome is disrupted.
  • Example: E. coli moving from the gastrointestinal tract to the urinary tract can cause a UTI.
• Decreased Immunity: Fighting a primary infection can weaken the immune system, making it more susceptible to secondary infections.
  • Example: Treatment with antibiotics can kill pathogens, but it also destroys the normal microbiome. This can lead to secondary infections..

Pathogen Exit

• To be transmitted to a new host, pathogens must exit the existing host (skin, respiratory tract, urogenital, GI).

Virulence Factors

• Virulence Factors: Promote pathogenicity and help pathogens adhere, invade and evade host defenses. Examples include adhesins, exoenzymes, and toxins.
• Adhesins: Help pathogens attach to host cells.
• Exoenzymes: Help pathogens penetrate host tissues, and damage cells.
• Toxins: Harm host cells and interfere with body functions.

Virulence Factors: Exoenzymes

• Hyaluronidase: Breaks down hyaluronic acid; allows pathogens to penetrate tissues.
• Nucleases: Break down DNA; allows pathogens to disseminate.
• Phospholipases: Break down phospholipids; breaks host cell membranes.
• Proteases: Break down proteins; can inactivate antibodies.
• Collagenase: Breaks down collagen; helps spread pathogens.

Virulence Factors: Toxins

• Endotoxins: Released upon pathogen death; stimulate inflammatory response or cause organ system failure
• Exotoxins: Proteins; often highly potent and deadly.
• A-B Toxins: Having two parts (A = activity, B = binding); A-toxin enters the cell and B-toxin binds to the receptor to the cell.
• Membrane-disrupting toxins: Create pores in host cell membranes or disrupt cell membranes.
• Superantigens: Trigger excessive immune responses, resulting in a cytokine storm.

Virulence Factors: Evasion of Phagocytosis

• Capsules: Prevent phagocytosis (immune cell engulfment).
• Proteases: Degrade host cell antibodies
• Fimbriae: Block binding to complement
• Antigenic Variation: Microbes alter surface proteins to avoid recognition. Examples include Lyme Disease (Borrelia burgdorferi), and influenza.

Other factors

• ID50: The infectious dose needed to cause an infection in 50% of infected animals.
• LD50: The lethal dose needed to kill 50% of infected animals.
• Opportunistic Pathogens: Only cause disease in an immunocompromised host.
• Period of Disease/Stages of Infection: Incubation: No signs or symptoms. Prodromal: Mild symptoms. Period of illness: Severe symptoms. Period of decline: Symptoms improve. Period of convalescence: Return to normal.
• Infants can contact pathogens during Pregnancy or Birth: Example, Chlamydia and Gonorrhea infections resulting in blindness in infants if not treated by eye antibiotics.

Test your knowledge on the mechanisms through which microorganisms cause disease. This quiz covers key terms such as pathogens, infection stages, and the types of diseases. Understand how pathogens invade host tissues and the factors involved in pathogenicity.