1. Three months ago, a 53-year old woman had surgery and chemotherapy for breast cancer. Four
weeks ago, she developed a cough occasionally productive of purulent sputum. About 2 weeks ago,
she noted a slight but progressive weakness of the left arm and leg. On chest examination, rales
were heard over the left upper back when the patient breathed deeply. Neurologic examination
confirmed weakness of the left arm and leg. Chest radiography showed a left upper lobe infiltrate.
Contrast-enhanced computed tomography showed two lesions in the right hemisphere. Gram stain
of a purulent sputum specimen showed branching Gram-positive rods that were partially acid fast.
Which of the following organisms is the cause of this patient’s current illness?
(A) Actinomyces israelii
(B) Corynebacterium pseudodiphtheriticum
(C) Aspergillus fumigatus
(D) Nocardia farcinica
N farcinica is Gram-positive and partially acid-fast. It is known to cause pneumonia and may
disseminate to the brain and manifest lesions.
(E) Erysipelothrix rhusiopathiae
A israelii is non acid-fast and causes the disease actinomycosis, also known as lumpy jaw.
C pseudodiphtheriticum causes pneumonia but is non acid-fast and is not reported to be invasive.
A fumigatus is a fungus and not a bacterium.
E rhusiopathiae is non acid-fast and causes erysipeloid, which is cutaneous.
2. The drug of choice to treat this patient’s infection is
(A) Penicillin G
(B) Trimethoprim-sulfamethoxazole
The drug of choice for nocardiosis is trimethoprim-sulfamethoxazole. Alternative
drugs include amikacin, imipenem, minocycline, linezolid, and cefotaxime.
(C) Gentamicin
(D) Amphotericin B
(E) A third-generation cephalosporin
3. It is particularly difficult to differentiate Erysipelothrix rhusiopathiae
(A) Corynebacterium diphtheriae
(B) Bacillus cereus
(C) Actinomyces israelii
(D) Nocardia asteroides
(E) Lactobacillus species
E rhusiopathiae and the Lactobacillus spp are both catalase-negative,
nonsporeforming, Gram-positive rods.
C diphtheriae is a Gram-positive bacillus but catalase-positive.
B cereus is a Gram-positive bacillus but sporeforming.
A israelii and N asteroides are both nonsporeforming, Gram-positive bacilli but they exhibit branching.
4. Movement of Listeria monocytogenes inside of host cells is caused by
(A) Inducing host cell actin polymerization
L monocytogenes induces host cell actin polymerization through the actin assembly-
inducing protein (ActA), generating an actin comet tail.
(B) The formation of pili (fimbriae) on the listeriae surface
(C) Pseudopod formation
weeks ago, she developed a cough occasionally productive of purulent sputum. About 2 weeks ago,
she noted a slight but progressive weakness of the left arm and leg. On chest examination, rales
were heard over the left upper back when the patient breathed deeply. Neurologic examination
confirmed weakness of the left arm and leg. Chest radiography showed a left upper lobe infiltrate.
Contrast-enhanced computed tomography showed two lesions in the right hemisphere. Gram stain
of a purulent sputum specimen showed branching Gram-positive rods that were partially acid fast.
Which of the following organisms is the cause of this patient’s current illness?
(A) Actinomyces israelii
(B) Corynebacterium pseudodiphtheriticum
(C) Aspergillus fumigatus
(D) Nocardia farcinica
N farcinica is Gram-positive and partially acid-fast. It is known to cause pneumonia and may
disseminate to the brain and manifest lesions.
(E) Erysipelothrix rhusiopathiae
A israelii is non acid-fast and causes the disease actinomycosis, also known as lumpy jaw.
C pseudodiphtheriticum causes pneumonia but is non acid-fast and is not reported to be invasive.
A fumigatus is a fungus and not a bacterium.
E rhusiopathiae is non acid-fast and causes erysipeloid, which is cutaneous.
2. The drug of choice to treat this patient’s infection is
(A) Penicillin G
(B) Trimethoprim-sulfamethoxazole
The drug of choice for nocardiosis is trimethoprim-sulfamethoxazole. Alternative
drugs include amikacin, imipenem, minocycline, linezolid, and cefotaxime.
(C) Gentamicin
(D) Amphotericin B
(E) A third-generation cephalosporin
3. It is particularly difficult to differentiate Erysipelothrix rhusiopathiae
(A) Corynebacterium diphtheriae
(B) Bacillus cereus
(C) Actinomyces israelii
(D) Nocardia asteroides
(E) Lactobacillus species
E rhusiopathiae and the Lactobacillus spp are both catalase-negative,
nonsporeforming, Gram-positive rods.
C diphtheriae is a Gram-positive bacillus but catalase-positive.
B cereus is a Gram-positive bacillus but sporeforming.
A israelii and N asteroides are both nonsporeforming, Gram-positive bacilli but they exhibit branching.
4. Movement of Listeria monocytogenes inside of host cells is caused by
(A) Inducing host cell actin polymerization
L monocytogenes induces host cell actin polymerization through the actin assembly-
inducing protein (ActA), generating an actin comet tail.
(B) The formation of pili (fimbriae) on the listeriae surface
(C) Pseudopod formation
