Ch. 21 - Microbial Diseases of the Skin and Eyes

Tortora - Microbiology: An Introduction 14th Edition

Tortora14th EditionMicrobiology: An IntroductionISBN: 9780138200398Not the one you use?Change textbook

Tortora 14th Edition

Ch. 21 - Microbial Diseases of the Skin and Eyes

Problem 9a

Chapter 21, Problem 9a

Use the following choices to answer the question given below.
a. Pseudomonas
b. Staphylococcus aureus
c. Scabies
d. Sporothrix
e. Virus
Microscopic examination of scrapings from the patient’s rash shows gram-negative rods.

Verified step by step guidance

Step 1: Identify the key information given in the problem, which is that microscopic examination of scrapings from the patient's rash shows gram-negative rods. This means the causative agent is a bacterium that stains pink/red with Gram stain and has a rod shape.

Step 2: Review the provided choices and classify each by their characteristics: (a) Pseudomonas - gram-negative rods; (b) Staphylococcus aureus - gram-positive cocci; (c) scabies - a mite (not bacteria); (d) Sporothrix - a fungus; (e) virus - not visible by Gram stain and not bacteria.

Step 3: Since the microscopic result shows gram-negative rods, eliminate options that are not gram-negative rods: Staphylococcus aureus (gram-positive cocci), scabies (mite), Sporothrix (fungus), and virus (not bacteria).

Step 4: Conclude that the most appropriate choice based on the microscopic description is Pseudomonas, which is a gram-negative rod-shaped bacterium.

Step 5: Understand that this approach uses the Gram stain characteristics and morphology to narrow down the causative agent from the given options.

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Key Concepts

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

Gram Staining and Bacterial Classification

Gram staining differentiates bacteria into gram-positive or gram-negative based on cell wall structure. Gram-negative bacteria have a thin peptidoglycan layer and an outer membrane, appearing pink/red under a microscope. This classification helps identify bacterial types and guides treatment decisions.

Morphology of Bacteria

Bacterial morphology refers to the shape and arrangement of bacteria, such as rods (bacilli), spheres (cocci), or spirals. Identifying rod-shaped bacteria (gram-negative rods) narrows down possible pathogens and aids in diagnosis and treatment.

Common Pathogens Associated with Skin Rashes

Certain bacteria and other organisms cause skin rashes, including gram-negative rods like Pseudomonas. Understanding which pathogens are linked to skin infections helps correlate microscopic findings with clinical symptoms for accurate diagnosis.

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Related Practice

Textbook Question

Use the following choices to answer questions 8–10:

a. Apicomplexa

b. Ciliates

c. Dinoflagellates

d. Microsporidia

These are nonmotile parasites with special organelles for penetrating host tissue.

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Textbook Question

This anaerobic, gram-positive rod is found on the skin. Infections are often treated with retinoids or benzoyl peroxide.

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Textbook Question

Which of the following pairs is mismatched?

a. Leading infectious cause of blindness—Chlamydia

b. Chickenpox—shingles

c. HSV-1—encephalitis

d. Buruli ulcer—stomach acid

e. None of the above

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Textbook Question

A patient exhibits inflammatory skin lesions that itch intensely. Microscopic examination of skin scrapings reveals an eight-legged arthropod. What is your diagnosis? How is the disease treated? What would you conclude if you saw a six-legged arthropod?

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Textbook Question

Use the following choices to answer the question given below.

a. Pseudomonas

b. Staphylococcus aureus

c. Scabies

d. Sporothrix

e. Virus

Microscopic examination of the patient’s ulcer reveals 10μm ovoid cells.

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