Microbiology Case Study: A 69 Year Old Male with Cardiac Symptoms

Case History

A 69 year old male with complicated past medical history of sarcoidosis, pulmonary nodules, atrial flutter, right septic arthritis, pulmonary embolism and coronary artery disease presented to the emergency department with worsening cardiac symptoms for the past few days. He denied any symptoms of fever, cough, dyspnea, or palpitations. He has no history of TB exposure, high-risk occupation or volunteer work. Chest x-ray, echocardiogram and computerized tomography (CT) scan were performed and he was diagnosed with constrictive pericarditis. Pericardiotomy was performed which showed thickened and calcified pericardium. On pericardial biopsy specimen, acute necrotizing and granulomatous pericarditis was identified (Image 1). Acid fast bacteria stain for mycobacteria was performed which showed numerous acid-fast bacilli (Image 2). In house validated testing for M. tuberculosis by PCR amplification of the IS6110 insertion sequence and nontuberculous mycobacteria species determination by heat shock protein 65 (hsp65) gene with melt curve analysis was performed. Testing was negative for M. tuberculosis. Nontuberculous mycobacteria testing was consistent with M. xenopi. For definitive diagnosis, culture was performed which grew M. xenopi (Image 3).

Image 1. H&E stain shows acute necrotizing granulomatous inflammation.
Image 2. Ziehl Neelsen stain shows numerous AFB positive bacilli.
Image 3. Lowenstein Jensen (LJ) media growing M. xenopi.


M. Xenopi is a free-living nontuberculous mycobacterium (NTM). NTM are present in the environment, mainly in water, and are occasionally responsible for opportunistic infections in humans.1 With the availability of 16S ribosomal DNA sequencing and high-performance liquid chromatography (HPLC), polymerase chain reaction-restriction length polymorphism analysis (PRA), and multi-gene and whole-genome sequencing, the number of new species of nontuberculous mycobacteria has risen dramatically. There are about 180 different species of mycobacteria. The most common nontuberculous species causing human disease in the United States are the slowly growing species, Mycobacterium avium complex and M. kansasii. Less common human pathogens include the slowly growing species M. marinumM. xenopiM. simiaeM. malmoense, and M. ulcerans, and the rapidly growing species M. abscessus complex, M. fortuitum, and M. chelonae.2 NTM can cause pulmonary disease, osteomyelitis or disseminated disease in immunocompromised patients.

Microscopic examination after acid fast or fluorescent Auramine-Rhodamine staining and AFB culture using LJ and Middlebrook 7H10 media are the cornerstones of the identification of mycobacteria. All mycobacteria share the characteristic of “acid-fastness,” ie, after staining with carbol-fuchsin or auramine-rhodamine, they do not decolorize with acidified alcohol. Confirmation of the presence or absence of mycobacteria in clinical specimens requires culture, because of the relative insensitivity of direct microscopy.

The presented case highlights the importance of NTM causing infection in pericardium which is very rare. Special stains, molecular testing, and culture can aid in timely identification of the organism and aid in patient management.


  1. Tortoli E. Microbiological features and clinical relevance of new species of the genus Mycobacterium. Clin Microbiol Rev 2014; 27:727.
  2. Griffith DE, Epidemiology of nontuberculous mycobacterial infections. Reyn CF UpToDate. April 2017.
  3. Griffith DE, Microbiology of nontuberculous mycobacteria. Reyn CF UpToDate. Sept 2018.

-Amandeep Kaur, MD MBBS is a 2nd year anatomic and clinical pathology resident at University of Chicago (NorthShore). Academically, Amandeep has a particular interest in hematopathology.

-Erin McElvania, PhD, D(ABMM), is the Director of Clinical Microbiology NorthShore University Health System in Evanston, Illinois. Follow Dr. McElvania on twitter @E-McElvania. 

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