Microbiology Case Study: 80 Year Old Woman with Productive Cough

An 80 year old female presented to the emergency department complaining of a productive cough, three episodes of bright red blood stained sputum, persistent night sweats, fever, chills, and weight loss. Chest imaging revealed extensive centrilobular ground glass opacities, multiple pleural based nodules, and a cavitary lesion. The patient was exposed to Mycobacterium tuberculosis as a child when her father was treated for an active infection. Direct smears were negative; respiratory cultures were performed and an AFB culture bottle flagged positive with the following gram stain and culture morphology.

Poor-staining, beaded Gram positive bacilli in clumps and cords.
Poor-staining, beaded Gram positive bacilli in clumps and cords.

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Laboratory identification:

The organism was auramine fluorescent stain positive from the broth. The AFB culture bottle was sub-cultured to agar based medium in addition to Lowenstein-Jensen medium, which yielded buff colored colonies with a dry bread-crumb like appearance, raising concern for Mycobacterium tuberculosis. Species identification was confirmed by DNA probe.

Discussion:

Definitive diagnosis of Mycobacterium tuberculosis is based on microscopy, culture, and/or PCR. The organisms are typically acid fast, straight or slightly curved rods that occur singly or in small clumps in clinical specimens. They may grow as twisted rope-like colonies called serpentine cords in liquid medium and take up to 2-4 weeks to grow in culture. They are obligate aerobes.

TB is transmitted by inhalation of bacilli in contaminated respiratory droplets. In an immunocompetent host, primary, latent, or reactivation pulmonary infection may occur. Reactivation disease and disseminated (military) disease is possible in immunocompromised patients including those with HIV, transplant recipients, and the elderly. TB also causes meningitis, pleurisy, and spinal infections.

The virulence of the organism is likely multifactorial and is believed to be related to its ability to survive within macrophages. It is treated with multi-drug antimicrobial therapy.

 

-Lauren Pearson, D.O. is a 2nd year anatomic and clinical pathology resident at the University of Vermont Medical Center.

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-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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