Ch. 25 - Microbial Diseases of the Digestive System

Tortora - Microbiology: An Introduction 14th Edition

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Tortora 14th Edition

Ch. 25 - Microbial Diseases of the Digestive System

Problem 4

Chapter 25, Problem 4

E. coli bacteria are part of the normal microbiota of the intestines and can cause gastroenteritis. Explain why this one species is both beneficial and harmful.

Verified step by step guidance

Step 1: Understand that Escherichia coli (E. coli) is a species of bacteria commonly found in the intestines of humans and animals, where it plays a role in the normal microbiota.

Step 2: Recognize the beneficial role of E. coli, which includes aiding in digestion, producing vitamin K, and preventing colonization by harmful pathogens through competitive exclusion.

Step 3: Identify that certain strains of E. coli can be harmful because they possess virulence factors such as toxins, adhesins, or invasins that can cause diseases like gastroenteritis.

Step 4: Explain that the harmful effects occur when pathogenic strains of E. coli contaminate food or water or when the balance of the normal microbiota is disrupted, allowing these strains to proliferate.

Step 5: Summarize that E. coli is both beneficial and harmful because it includes a diverse group of strains—some are harmless and essential for gut health, while others have acquired genetic traits that make them pathogenic.

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Key Concepts

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

Normal Microbiota and Symbiosis

Normal microbiota refers to the community of microorganisms that live harmlessly or beneficially within the human body. E. coli in the intestines aids digestion, synthesizes vitamins like vitamin K, and helps prevent colonization by harmful pathogens, demonstrating a mutualistic relationship.

Pathogenicity and Virulence Factors

Certain strains of E. coli possess virulence factors such as toxins, adhesins, and invasins that enable them to cause disease. These pathogenic strains can disrupt intestinal function, leading to gastroenteritis characterized by symptoms like diarrhea and abdominal pain.

Strain Diversity within a Species

E. coli is a diverse species with many strains, some harmless and others pathogenic. Genetic differences among strains determine their role as either beneficial commensals or harmful pathogens, explaining how one species can have both positive and negative effects on human health.

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Textbook Question

Microscopic examination of a patient’s fecal culture shows comma-shaped bacteria. These bacteria require 2-4% NaCl to grow. The bacteria probably belong to the genus

a. Campylobacter.

b. Escherichia.

c. Salmonella.

d. Shigella.

e. Vibrio.

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Textbook Question

Isolation of E. coli from a stool sample is diagnostic proof that the patient has

a. Cholera.

b. E. coli gastroenteritis.

c. Salmonellosis.

d. Typhoid fever.

e. None of the above

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Textbook Question

Gastric ulcers are caused by

a. Stomach acid.

b. H. pylori.

c. Spicy food.

d. Acidic food.

e. Stress.

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Textbook Question

Identify the site colonized by the following organisms: E. granulosus, E. vermicularis, Giardia, H. pylori, hepatitis B virus, mumps virus, Rotavirus, Salmonella, Shigella, Streptococcus mutans, Trichinella spiralis, Trichuris.

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Textbook Question

Define mycotoxin. Give an example of a mycotoxin.

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Textbook Question

Explain how the following diseases differ and how they are similar: giardiasis, amebic dysentery, cyclosporiasis, and cryptosporidiosis.

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