A 54-year-old woman is brought to the emergency department after a generalized tonic-clonic seizure. The patient had fever, night sweats, fatigue, and productive cough during the previous week. She underwent a renal transplant 2 years ago and takes immunosuppressive therapy. On examination, she is febrile and postictal. There are scattered lung crackles and normal heart sounds. Leukocyte count is elevated, and chest x-ray reveals patchy bronchopneumonia with several nodules. Brain imaging shows multifocal abscesses. Sputum Gram stain reveals filamentous, branching gram-positive rods as shown below: This pathogen is likely to demonstrate which of the following characteristics?

Question

A 54-year-old woman is brought to the emergency department after a generalized tonic-clonic seizure.  The patient had fever, night sweats, fatigue, and productive cough during the previous week.  She underwent a renal transplant 2 years ago and takes immunosuppressive therapy.  On examination, she is febrile and postictal.  There are scattered lung crackles and normal heart sounds.  Leukocyte count is elevated, and chest x-ray reveals patchy bronchopneumonia with several nodules.  Brain imaging shows multifocal abscesses.  Sputum Gram stain reveals filamentous, branching gram-positive rods as shown below:  This pathogen is likely to demonstrate which of the following characteristics?

Quizplus · Accepted Answer

11ec160b_38a0_dbe3_9249_ffad8a4c1a7e_MD0001_00 This patient with bronchopneumonia, brain abscesses, and branching, filamentous bacteria on sputum culture likely has Nocardia infection. Nocardia is a ubiquitous organism found in soil that is transmitted by inhalation or inoculation into the skin. Because the pathogen has minimal virulence, those with impaired cell-mediated immunity (eg, immunosuppressive therapy, AIDS) are at greatest risk. Bronchopneumonia is the most common manifestation. Patients usually have cough, purulent sputum, and pulmonary nodules or cavitations. Spread through the bloodstream to the brain occurs in up to 50% of cases and can lead to multiloculated brain abscesses and seizures. The microscopic appearances of Nocardia and Actinomyces are similar; both organisms are gram-positive and grow in branching filaments that resemble the hyphae of fungus. However, unlike Actinomyces, Nocardia has mycolic acid in its cell wall, which causes it to stain partially acid-fast. (Choice A) Actinomyces is an anaerobic organism that primarily causes cervicofacial infections characterized by chronic, nonpainful, mandibular swelling with abscesses, draining sinuses, and sulfur granules. (Choice B) Aspergillus species can cause angioinvasive pneumonia (classic triad of fever, pleuritic chest pain, and hemoptysis) in patients who are immunocompromised. However, sputum microscopy typically reveals septate hyaline hyphae, not branching, filamentous, gram-positive bacteria. (Choice C) Mycobacterium tuberculosis is an acid-fast mycobacterium that is inhaled into the lungs and replicates intracellularly. Although M tuberculosis can grow in long, serpentine cords due to the presence of cord factor, it does not grow in thin, branching filaments. In addition, the presence of brain abscesses makes Nocardia far more likely. (Choice E) Clostridium perfringens is a common cause of food poisoning and can also cause gas gangrene/myonecrosis through the generation of a phospholipase exotoxin. Although C perfringens is a gram-positive bacillus, it does not form branching filaments in culture. Educational objective: Nocardia is a filamentous, branching, gram-positive bacteria that is partially acid-fast. It most commonly causes pneumonia and brain abscesses in immunocompromised patients.

A 54-Year-Old Woman Is Brought to the Emergency Department After