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Ch. 10 - Host Microbe Interactions and Pathogenesis
Norman-McKay- Microbiology: Basic and Clinical Principles 2nd Edition
Norman-McKay2nd EditionMicrobiology: Basic and Clinical PrinciplesISBN: 9780137661619Not the one you use?Change textbook
All textbooksNorman-McKay 2nd EditionCh. 10 - Host Microbe Interactions and PathogenesisProblem 3
Chapter 10, Problem 3

Define the class of each listed exotoxin as type I, II, or III:
a. Superantigen
b. Hemolysins
c. Staphylococcus aureus enterotoxins that cause food poisoning
d. AB toxin
e. Membrane-damaging toxins
f. Phospholipases

Verified step by step guidance
1
Understand the classification of exotoxins into three types based on their mechanism of action: Type I (superantigens), Type II (membrane-damaging toxins), and Type III (A-B toxins).
Identify that Type I exotoxins, or superantigens, bind to immune receptors and cause massive immune activation without entering the cell.
Recognize that Type II exotoxins damage host cell membranes directly, including hemolysins and phospholipases, which disrupt membrane integrity.
Know that Type III exotoxins are A-B toxins composed of two parts: the A (active) subunit that exerts toxicity inside the cell, and the B (binding) subunit that attaches to the host cell surface.
Classify each listed exotoxin accordingly: superantigens as Type I, hemolysins and phospholipases as Type II, Staphylococcus aureus enterotoxins (which are superantigens) as Type I, AB toxins as Type III, and membrane-damaging toxins as Type II.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Classification of Exotoxins (Type I, II, III)

Exotoxins are classified into three types based on their mechanism of action: Type I toxins (superantigens) bind to cell surface receptors and trigger immune responses without entering cells; Type II toxins (membrane-damaging toxins) disrupt cell membranes causing lysis; Type III toxins (AB toxins) have two components where the B subunit binds the cell and the A subunit exerts enzymatic activity inside the cell.
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Types of Exotoxins

Superantigens and Their Role

Superantigens are a class of Type I exotoxins that non-specifically activate large numbers of T-cells by linking MHC class II molecules to T-cell receptors, leading to massive cytokine release and systemic immune responses. Examples include certain Staphylococcus aureus enterotoxins causing toxic shock and food poisoning.
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3) Superantigens

Membrane-Damaging Toxins and Phospholipases

Membrane-damaging toxins (Type II) include hemolysins and phospholipases that disrupt host cell membranes by forming pores or enzymatically degrading phospholipids. Hemolysins lyse red blood cells, while phospholipases hydrolyze membrane phospholipids, both leading to cell death and tissue damage.
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2) Membrane-Damaging Toxins
Related Practice
Textbook Question

Indicate the true statements and then correct the false statements so that they are true.

a. HIV is transmitted by a parenteral route.

b. Candida albicans is an opportunistic pathogen that can cause disease in an immune-competent host if the normal microbiota are disrupted.

c. Gram-positive bacteria may produce endotoxin.

d. Siderophores help pathogens obtain calcium.

e. Emerging pathogens tend to exhibit expanded tropism.

f. The more toxic a substance is, the higher its LD50.

g. Virulence is the ability of a microbe to cause disease.

h. Gram-negative bacteria may produce exotoxins.

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Textbook Question

Assume your patient has a superantigen circulating in their blood. Select the single statement that is most likely to apply to your patient.

a. They are at risk for endotoxic shock.

b. They are not up to date on their vaccinations.

c. They are infected with a Gram-positive microbe.

d. They do not have a fever.

e. They have a viral infection.

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Textbook Question

Select the false statement about normal microbiota.

a. They compete with pathogens.

b. They do not include potential pathogens.

c. They make vitamins for the host.

d. They train the immune system.

e. A disruption in their balance can lead to disease.

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Textbook Question

Which of the following is a true statement?

a. If a pathogen establishes an infection, it is described as virulent.

b. Pathogenicity is the extent of disease caused by a microbe.

c. Normal microbiota are not usually affected by host factors.

d. A pathogen’s virulence factors change over time in response to selective pressures.

e. Attenuated pathogens cause disease in a normal host.

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Textbook Question

Which of the following is true regarding tropism?

a. It is the preference of a pathogen for a given tissue.

b. It is constant for a given microbe.

c. It limits a pathogen to infecting only one host.

d. It is determined by portal of entry.

e. It is independent of host factors.

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