An AIDS patient develops symptoms suggestive of a severe

An AIDS patient develops symptoms suggestive of a severe, persistent pneumonia with
cough, fever, chills, chest pain, weakness, and weight loss. The patient does not respond to
penicillin therapy, but goes on to develop very severe headaches. The presence of focal
neurologic abnormalities leads the clinician to order a CT scan of the head. This demonstrates
several metastatic brain abscesses. Biopsy of one of these lesions demonstrates beaded,
branching, filamentous gram-positive bacteria that are weakly acid fast. Which of the following
is the most likely causative organism?

A. Actinomyces
B. Aspergillus
C. Burkholderia
D. Francisella
E. Nocardia

Explanation:
The correct answer is E.Nocardia asteroides is an aerobic soil saprophyte that can cause acute or
chronic infectious disease often characterized by granulomatous-suppurative lesions that may
become widely disseminated. Many, but not all, patients have underlying causes for
immunodeficiency, including advanced age, lymphoreticular malignancies, organ
transplantation, high dose corticosteroid therapy, or (increasingly commonly) AIDS.
Disseminated nocardiosis usually starts as a pulmonary infection that can resemble either a
severe pneumonia or tuberculosis. Once dissemination occurs, metastatic brain abscesses are
particularly common, occurring in as many as 1/3 of patients with nocardiosis. Nocardiosis is
treated with sulfa drugs, such as sulfadiazine or trimethoprim-sulfamethoxazole, for periods of
months.
Actinomyces (choice A) is very similar to Nocardia, but is not acid-fast.
Aspergillus(choice B) is a fungus.
Burkholderia(choice C)pseudomallei is a gram-negative bacillus that causes melioidosis, which
is characterized by lung involvement or disseminated infection.
Francisella(choice D)tularensis causes tularemia, which is usually acquired by contact with
infected wild rabbits.