Ch. 16 - Innate Immunity: Nonspecific Defenses of the Host

Tortora - Microbiology: An Introduction 14th Edition

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Tortora 14th Edition

Ch. 16 - Innate Immunity: Nonspecific Defenses of the Host

Problem 5

Chapter 16, Problem 5

A human host can prevent a pathogen from getting enough iron by all of the following except
a. reducing dietary intake of iron.
b. binding iron with transferrin.
c. binding iron with hemoglobin.
d. binding iron with ferritin.
e. binding iron with siderophores.

Verified step by step guidance

Step 1: Understand the biological context of iron withholding as a host defense mechanism. The human body limits free iron availability to pathogens because iron is essential for microbial growth and metabolism.

Step 2: Review the roles of the listed molecules in iron binding: transferrin binds free iron in blood plasma, ferritin stores iron intracellularly, and hemoglobin carries oxygen in red blood cells by binding iron within heme groups.

Step 3: Recognize that siderophores are molecules secreted by bacteria (pathogens) to scavenge iron from the host environment, not a host protein that binds iron to prevent pathogen access.

Step 4: Analyze each option to determine which one does not represent a host strategy to limit iron availability to pathogens. The host reduces dietary iron intake, uses transferrin, ferritin, and hemoglobin to sequester iron, but does not use siderophores for this purpose.

Step 5: Conclude that the correct answer is the option involving siderophores, as they are microbial iron-binding molecules, not a host defense mechanism.

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Key Concepts

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

Iron Sequestration in Host Defense

The human body limits pathogen growth by restricting free iron availability, a process called nutritional immunity. Proteins like transferrin and ferritin bind iron tightly, reducing its accessibility to microbes and thus inhibiting their proliferation.

Role of Iron-Binding Proteins

Transferrin transports iron in the blood, ferritin stores iron intracellularly, and hemoglobin carries oxygen bound to iron in red blood cells. These proteins help sequester iron, making it less available to invading pathogens.

Siderophores and Microbial Iron Acquisition

Siderophores are molecules secreted by bacteria to scavenge iron from the host environment. Unlike host proteins, siderophores bind iron to facilitate microbial uptake, thus promoting pathogen survival rather than restricting iron availability.

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