Microbiology Case Study

Patient History:

81 year old man with a history of systemic vasculitis (present for the past 10 years ANCA negative, ANA negative, Rheumatoid factor <20) on immunosuppression (plaquenil with prednisone 40mg for flares about every 6 months), type 2 diabetes, and hypertension presented to an outside hospital with weakness and dyspnea. He was found to have a widespread purpura, ulcerative lesions, acute kidney injury (creatinine 4.7), and 3 days of hematochezia. He was started on 7 days of levoquin and zosyn for a presumed pneumonia and with no improvement was transferred to our institution. On admission, a CT scan of the chest demonstrated bilateral multifocal pneumonia and multiple cavitary nodules within the lungs. A thoracentesis was performed and was transudative (wbc 1883, N 63%, protein 2.6).

Laboratory findings:

  • WBC 7000/cmm
  • Hemoglobin 9 g/dL
  • Platelet count 104 K/cmm
  • Bacterial culture blood, no growth
  • Cryptococcal antigen negative
  • Pleural fluid bacterial culture and smear negative
  • Pleural fluid AFB culture and smear – no acid fast bacilli, modified acid fast bacilli seen from bottle
  • Pleural fluid fungal culture and smear – no fungi seen, rare modified acid fast bacilli growing
  • Histoplasma urinary antigen positive
  • Histoplasma antibodies negative
  • Blastomyces urinary antigen negative
Gram stain of growth from the AFB bottle showing beaded, branch Gram positive bacilli.
Gram stain of growth from the AFB bottle showing beaded, branch Gram positive bacilli.
Modified acid fast stain of growth from the AFB bottle showing modified acid fast bacilli.
Modified acid fast stain of growth from the AFB bottle showing modified acid fast bacilli.
Isolated growth on BCYE media.
Isolated growth on BCYE media.

Discussion:

Based on Gram stain and modified acid fast stain, modified acid fast bacilli suggestive of Nocardia species was reported. Nocardia are strict aerobic, gram positive, filamentous rods that stain partially acid fast. This is due to the mycolic acids in the cell wall which are shorter than those of mycobacteria. Nocardia species produce many virulence factors including Cord factor (prevents intracellular killing), catalase and superoxide dismutase (which inactivate reactive oxygen species that would otherwise prove toxic to the bacteria).

Nocardia grow well on buffered charcoal yeast extract agar and at 30oC. They produce aerial hyphae and can have a chalky colony appearance. Species level identification is best done with molecular methods. This isolate was identified as Nocardia farcinica at a reference laboratory.

Nocardia species are ubiquitous in the soil. They can cause infections in immunocompromised hosts usually after inhalation or direct inoculation. Infections include bronchopulmonary disease and cutaneous infections. With bronchopulmonary disease, cavitation and spread to the pleura is common, which fits with our patient. Dissemination is also seen with common sites being brain and subcutaneous tissue.

Our patient had a positive Histoplasma urinary antigen, but negative Histoplasma antibodies. The working diagnosis was disseminated Histoplasmosis and he was being treated with amphotericin B. He expired and no postmortem exam was performed. Fungal cultures from the pleural fluid were not growing fungus at the time of this post. Fungal cultures were not obtained from sputum and a BAL was not performed.

-Dan Olsen, MD is a 4th year anatomic and clinical pathology resident at the University of Vermont Medical Center.

Wojewoda-small

-Christi Wojewoda, MD, is the Director of Clinical Microbiology at the University of Vermont Medical Center and an Assistant Professor at the University of Vermont.

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