Microbial Mechanisms of Pathogenesis

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Questions and Answers

What is the first step a pathogen must take to cause disease?

Damage host tissues

Evade host defenses

Adhere to host tissues

Gain access to the host (correct)

Which of the following is NOT classified as a portal of entry for pathogens?

Mucous membranes

Skin

Nervous system (correct)

Respiratory tract

What does the term 'infectious dose (50%)' or ID50 refer to?

The number of organisms necessary for infection in 50% of hosts (correct)

The average count of bacteria in a chronic infection

The total number of pathogens required for disease symptoms

The number of organisms needed to kill 50% of a population

Which component acts as a barrier to phagocytosis for pathogens like S.pneumoniae?

Capsule Signup and view all the answers

Which of the following toxins is noted for its extremely low lethal dose (LD50)?

Botulinum toxin Signup and view all the answers

What role do adhesins play in the process of microbial pathogenesis?

They enable adherence to host tissues Signup and view all the answers

Which mechanism is used by pathogens for antigenic variation?

Altering surface antigens Signup and view all the answers

What are biofilms primarily composed of?

Communities of microbes Signup and view all the answers

What is one method by which pathogens can directly damage host tissues?

Using host iron through siderophores Signup and view all the answers

What type of toxins are exotoxins primarily associated with?

Soluble proteins that inhibit cellular functions Signup and view all the answers

Which of the following is a common portal of exit for pathogens?

Respiratory tract Signup and view all the answers

How do endotoxins typically affect the host organism?

By stimulating cytokine release at high concentrations Signup and view all the answers

Infection induced by which of the following typically signals that a pathogen is present?

Protozoa presence Signup and view all the answers

What is a characteristic feature of exotoxins compared to endotoxins?

Exotoxins can be neutralized by anti-toxins Signup and view all the answers

Which of the following is a consequence of high concentrations of endotoxins in the bloodstream?

Decreased blood pressure leading to septic shock Signup and view all the answers

Which type of bacterial toxin is primarily responsible for tissue septicity in Gram-negative infections?

Endotoxins (Lipid A) Signup and view all the answers

Study Notes

Microbial Mechanisms of Pathogenesis

Pathogens must gain access to a host, adhere to host tissues, and penetrate/evade host defenses to cause disease.
Portal of Entry:
- Mucous membranes (respiratory, gastrointestinal, genitourinary, conjunctiva)
- Skin
- Parenteral route (punctures, injections, bites, surgery)
- Preferred portal is prerequisite for disease, often determined by Table 15.1 on page 425.
Adherence:
- Adhesins (molecules on microbes; glyco/lipoproteins) bind to receptors (host surface molecules; sugars)
- Biofilms are communities of microbes (e.g., dental plaque, algae, shower scum) that work together.

Damage to Host Cells

Pathogens commonly use host nutrients (mainly iron) to generate cellular damage.
- Siderophores are iron-scavenging proteins used by pathogens.
Several methods of direct damage include rupture of cells after invasion and spread to other tissues.
- Cell damage may also lead to the spread of toxins.
Toxins (Fig 15.4, page 431):
- Exotoxins (G+):
  - Proteins produced inside pathogenic bacteria (mostly gram-positive).
  - Released during log phase.
  - Inhibit cellular functions specifically within the infected tissue.
  - The host produces antitoxins for immunity.
    - A-B toxins are a category of exotoxins (see Figure 15.5).
- Endotoxins (LPS Lipids):
  - Lipid portions of lipopolysaccharides (LPS) found in the outer membrane of gram-negative bacteria.
  - Released when bacterial cells die/breakdown.
  - Produce general effects in the host, such as fever, weaknesses, aches and shock.
  - Stable, so they can survive autoclaving.

Other Bacterial Causes of Pathogenicity

Plasmids:
- R factors are a type of plasmid.
Virulent plasmids (confer virulence)
Bacteriophage (bacteriophages)=lysogemy: Bacteriophages can cause lysogenic conversion where the infection only becomes pathogenic when the host cell is infected by lysogenic viruses.

Pathogenicity of Other Microbes

Viruses: intracellular parasites; cytopathic effects
Fungi: produce toxins that cause infection
Protozoa: presence alone signals infection
Helminths: (worms)
Algae: Produce neurotoxins

Portal of Exit

Generally, the portal of exit reflects the initial portal of entry
Common exit portals: gastrointestinal tract, genitourinary tract, respiratory tract, and conjunctiva.

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Description

Explore the intricate processes by which pathogens invade hosts and cause disease. This quiz covers the portals of entry, adherence mechanisms, and methods pathogens use to damage host cells. Test your knowledge on the fundamental concepts of microbial pathogenesis.