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 10

Chapter 21, Problem 10

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

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Identify the key characteristics given: the bacterium is anaerobic, gram-positive, rod-shaped, and found on the skin.

Recall common anaerobic, gram-positive rods associated with skin flora; consider genera such as Propionibacterium (now Cutibacterium) and Clostridium.

Focus on the clinical context: infections treated with retinoids or benzoyl peroxide are typically related to acne, which is commonly associated with Cutibacterium acnes (formerly Propionibacterium acnes).

Confirm that Cutibacterium acnes fits all criteria: it is an anaerobic, gram-positive rod found on the skin and involved in acne pathogenesis.

Conclude that the organism described is Cutibacterium acnes, based on morphology, oxygen requirements, habitat, and treatment options.

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Key Concepts

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

Anaerobic Gram-Positive Rods

Anaerobic gram-positive rods are bacteria that do not require oxygen for growth and have a thick peptidoglycan cell wall, staining purple in Gram stain. These bacteria often inhabit skin and mucous membranes and can be involved in various infections, especially in low-oxygen environments.

Skin Microbiota and Pathogens

The skin hosts diverse microorganisms, including commensal and pathogenic bacteria. Some anaerobic gram-positive rods, like Cutibacterium acnes, are part of normal skin flora but can cause infections such as acne when they proliferate excessively or trigger inflammation.

Treatment of Acne with Retinoids and Benzoyl Peroxide

Retinoids and benzoyl peroxide are common treatments for acne, targeting the bacteria and inflammation. Retinoids normalize skin cell turnover, while benzoyl peroxide has antimicrobial properties that reduce bacterial load, particularly effective against anaerobic bacteria like Cutibacterium acnes.

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Use the following choices to answer questions 8–10:

a. Apicomplexa

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c. Dinoflagellates

d. Microsporidia

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Use the following choices to answer the question given below.

a. Pseudomonas

b. Staphylococcus aureus

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e. Virus

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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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