What component of Mycoplasma cell membrane is unique?

Answer: It contains sterols like cholesterol and is the cell's only protective layer. Mycoplasma requires cholesterol for growth.

Why do penicillins and cephalosporins not work against Mycoplasma?

Answer: Mycoplasma has no cell wall, therefore, penicillins and cephalosporins which target the cell wall are ineffective.

How is nocardiosis treated?

Answer: Trimethoprim-sulfamethoxazole (TMP-SMX)

What risk factors predispose to Nocardia infection?

Answer: Immunosuppression and cancer

How does a Nocardia infection manifest?

Answer: Infection with Nocardia can produce pneumonia, lung abscesses, and can spread systemically. Abscesses can form throughout the body, especially in the brain.

How is Nocardia transmitted?

Answer: Transmitted via inhalation, producing lung abscesses and cavitations (it can be confused with Mycobacterium tuberculosis)

Does Nocardia require oxygen?

Answer: Yes. Nocardia is aerobic, in contrast to Actinomyces, an anaerobe.

Where is Nocardia normally found?

Answer: In the soil with transmission via inhalation. Nocardia is never a normal flora.

Describe the appearance of Nocardia asteroides on light microscopy:

Answer: Gram-positive rods forming branching, beaded filament S. Nocardia is also slightly acid-fast due to the mycolic acid in its cell walls.

How are Actinomyces infections treated?

Answer: Penicillin G (often for a prolonged course) +/- surgical drainage

How does an Actinomyces infection manifest?

Answer: Actinomyces causes eroding abscesses with draining sinus tracts. Main forms are cervicofacial (lumpy jaw) and thoracic. Also may cause pelvic pathology in females.

Can Actinomyces grow without oxygen?

Answer: Yes. Actinomyces is an anaerobe.

What are sulfur granules of Actinomyces?

Answer: Yellow-colored colonies and cellular debris (do not actually contain sulfur) that are visible within the purulent discharge

Where is Actinomyces normally found?

Answer: In the gingival crevices of the teeth, especially in patients with poor oral hygiene. It forms part of the normal oral flora.

Describe the appearance of Actinomyces israelii on light microscopy:

Answer: Gram-positive rods forming branching, beaded filaments. Colonies in pus appear as yellow granules called sulfur granules.

A 30-year-old woman from Southeast Asia presents with a hypopigmented, macular forearm lesion and associated with loss of sensation (decreased pin prick). The arm shows significant muscle atrophy. What is the most likely diagnosis?

Answer: Tuberculoid leprosy

A 34-year-old male immigrant presents to the physician with a cough and fever. On his last visit 12 months ago, his PPD was positive and chest x-ray showed likely active tuberculosis. He was treated with INH and rifampin and his symptoms abated. On this visit, he appears very sick and has hard time breathing. He denies night sweats and hemoptysis. His temperature is 102.1°F. Chest x-ray reveals infiltrates in the right middle and lower lobes and a Ghon complex. He is still taking INH and rifampin, which do not seem to help. What is the most likely diagnosis?

Answer: TB relapse; note that the Ghon complex is consistent with primary healed TB and does not exclude reactivation on relapse.

A patient presents with low-grade fever, chills, night sweats, weight loss, and a cough productive of blood-tinged sputum for 2 months. You suspect tuberculosis (TB) and order a chest x-ray. What findings on chest x-ray would be consistent with your suspected diagnosis?

Answer: Active tuberculosis pneumonia with cavitary lesions and posterior upper lobe involvement (past exposure would show isolated granuloma, Ghon focus, Ghon complex, old scarring in the upper lobes)

A 22-year-old woman is taking isoniazid prophylaxis for tuberculosis exposure. After 1 month of therapy she develops tingling in both her hands. What is the term for what she is experiencing and how would you treat her?

Answer: Peripheral neuropathy due to vitamin B6 depletion by the isoniazid (INH). Treat with vitamin B6, otherwise known as pyridoxine

What causes fish-tank or swimming-pool granuloma?

Answer: Mycobacterium marinum.

Granulomatous, ulcerating lesions at the site of breaks in the skin exposed to these environments