Textbook Question
Compare and contrast the following aspects of endotoxins and exotoxins: bacterial source, chemistry, toxigenicity, and pharmacology. Give an example of each toxin.
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Ch. 15 - Microbial Mechanisms of Pathogenicity
Tortora14th EditionMicrobiology: An IntroductionISBN: 9780138200398
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Table of contents
- Ch. 1 - The Microbial World and You18
- Ch. 2 - Chemical Principles20
- Ch. 3 - Observing Microorganisms Through a Microscope18
- Ch. 4 - Functional Anatomy of Prokaryotic and Eukaryotic Cells21
- Ch. 5 - Microbial Metabolism20
- Ch. 6 - Microbial Growth20
- Ch. 7 - The Control of Microbial Growth20
- Ch. 8 - Microbial Genetics19
- Ch. 9 - Biotechnology & DNA Technology20
- Ch. 10 - Classification of Microorganisms15
- Ch. 11 - The Prokaryotes: Domains Bacteria and Archaea14
- Ch. 12 - The Eukaryotes: Fungi, Algae, Protozoa, and Helminths17
- Ch. 13 - Viruses, Viroids, and Prions20
- Ch. 14 - Principles of Disease and Epidemiology21
- Ch. 15 - Microbial Mechanisms of Pathogenicity19
- Ch. 16 - Innate Immunity: Nonspecific Defenses of the Host20
- Ch. 17 - Adaptive Immunity: Specific Defenses of the Host20
- Ch. 18 - Practical Applications of Immunology20
- Ch. 19 - Disorders Associated with the Immune System19
- Ch. 20 - Antimicrobial Drugs19
- Ch. 21 - Microbial Diseases of the Skin and Eyes21
- Ch. 22 - Microbial Diseases of the Nervous System19
- Ch. 23 - Microbial Diseases of the Cardiovascular and Lymphatic Systems20
- Ch. 24 - Microbial Diseases of the Respiratory System20
- Ch. 25 - Microbial Diseases of the Digestive System20
- Ch. 26 - Microbial Diseases of the Urinary and Reproductive Systems19
- Ch. 27 - Environmental Microbiology20
- Ch. 28 - Applied and Industrial Microbiology19
Tortora14th EditionMicrobiology: An IntroductionISBN: 9780138200398Not the one you use?Change textbook
Chapter 15, Problem 6
Label this diagram to show how the Shiga toxin enters and inhibits protein synthesis in a human cell.
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Identify the receptor on the human cell surface that the Shiga toxin binds to; this is typically a glycolipid such as Gb3 (globotriaosylceramide).
Label the binding of the Shiga toxin's B subunit to the Gb3 receptor, which facilitates the toxin's entry into the cell via endocytosis.
Trace the intracellular trafficking of the toxin from the endosome to the Golgi apparatus and then to the endoplasmic reticulum (ER), highlighting the retrograde transport pathway.
Indicate the translocation of the A subunit of the Shiga toxin from the ER into the cytosol, where it exerts its toxic effect.
Show how the A subunit enzymatically modifies the 28S rRNA of the 60S ribosomal subunit by removing an adenine residue, thereby inhibiting protein synthesis and leading to cell damage.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Shiga Toxin Structure and Function
Shiga toxin is a bacterial exotoxin composed of an A subunit and multiple B subunits. The B subunits bind specifically to receptors on the host cell surface, facilitating toxin entry. The A subunit enzymatically inhibits protein synthesis by targeting ribosomes, leading to cell damage.
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03:40
Introduction to Pathogenic Toxins
Mechanism of Cellular Entry
Shiga toxin enters human cells via receptor-mediated endocytosis, where the B subunits bind to glycolipid receptors like Gb3 on the cell membrane. After internalization, the toxin is transported retrogradely through the Golgi apparatus to the endoplasmic reticulum, enabling the A subunit to reach the cytosol.
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02:29Entry & Uncoating by Endocytosis
Inhibition of Protein Synthesis
Once in the cytosol, the A subunit of Shiga toxin enzymatically removes an adenine base from the 28S rRNA of the 60S ribosomal subunit. This depurination halts elongation during translation, effectively inhibiting protein synthesis and causing cell death.
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05:03Enzyme Inhibition
Related Practice
Textbook Question
A drug that binds to mannose on human cells would prevent
a. the entrance of Vibrio enterotoxin.
b. the attachment of pathogenic E. coli.
c. the action of botulinum toxin.
d. streptococcal pneumonia.
e. the action of diphtheria toxin.
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Textbook Question
Describe the factors contributing to the pathogenicity of fungi, protozoa, and helminths.
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Textbook Question
The earliest smallpox vaccines were infected tissue rubbed into the skin of a healthy
person. The recipient of such a vaccine usually developed a mild case of smallpox, recovered, and was immune thereafter. What is the most likely reason this vaccine did not kill more people?
a. Skin is the wrong portal of entry for smallpox.
b. The vaccine consisted of a mild form of the virus.
c. Smallpox is normally transmitted by skin-to-skin contact.
d. Smallpox is a virus.
e. The virus mutated.
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Textbook Question
All of the following are related to bacterial infection. Which would prevent all of the others?
a. Vaccination against fimbriae
b. Phagocytosis
c. Inhibition of phagocytic digestion
d. Destruction of adhesins
e. Alteration of cytoskeleton
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Textbook Question
The ID₅₀ for Campylobacter sp. is 500 cells; the ID₅₀ for Cryptosporidium sp. is 100 cells. Which of the following statements is false?
a. Both microbes are pathogens.
b. Both microbes produce infections in 50% of the inoculated hosts.
c. Campylobacter is more virulent than Cryptosporidium.
d. Campylobacter and Cryptosporidium are equally virulent; they cause infections in the same number of test animals.
e. Cryptosporidium infections are acquired more easily than Campylobacter infections.