Microbiology Case Study: A 70 Year Old Male with Multiple Myeloma

Case History

The patient is a 70 year old male who was diagnosed with Kappa free light chain multiple myeloma. He was initially seen after he had a fall in the woods and underwent imaging which showed multiple lytic lesions and blood work showing monoclonal proteins and thrombocytopenia. He was found to have a lesion on his right scapula for which he received radiation. Bone marrow biopsy was performed which showed 60% plasma cells. To date he has completed radiation therapy, 5 cycles of chemotherapy, and is in the process of collecting stem cells for autologous stem cell transplant. Routine fungal culture of the stem cell collection grew a single tan white dry appearing colony on potato flake agar. A Gram stain of the organism revealed gram positive cocci mixed with filamentous structures.

Laboratory Identification

Image 1. Single tan white dry colony on potato flake agar.
Image 2. Modified acid fast stain (left) and Gram stain (right).
Image 3. Filamentous branching on Gram stain.

Based on the colony morphology and Gram stain results the organism was suspected to be in the Streptomyces genus. Identification with MALDI-TOF was attempted and did not yield a result as this bacteria is not in the data base.

Discussion

Streptomyces is a genus of gram positive aerobic saprophytic bacteria that grows in various environments, and has a filamentous form similar to fungi (1). The morphologic differentiation of Streptomyces involves identification of complex multicellular architecture with germinating spores that form hyphae, and multinuclear aerial mycelium, which forms septa at regular intervals, creating a chain of uninucleated spores (2,3). They are able to metabolize many different compounds including sugars, alcohols, amino acids, and aromatic compounds by producing extracellular hydrolytic enzymes (helping with degradation of organic matter). Their metabolic diversity is due to their extremely large genome which has hundreds of transcription factors that control gene expression, allowing them to respond to specific needs (3).

Streptomyces is also considered to be one of the most medically important bacteria because of its ability to produce bioactive secondary metabolites. These metabolites are used in the creation of antifungals, antivirals, antitumoral, anti-hypertensives, and many antibiotics and immunosuppressives. They are responsible for 2/3 of all the worlds naturally occurring antibiotics (1).

Streptomyces is usually considered a laboratory contaminant though they can cause infections in immunocompromised patients and are chiefly responsible for granulomatous lesions in skin also known as actinomycotic mycetomas (1,2). Invasive pulmonary disease has been seen in HIV patients, splenectomized patients with sarcoid, and rarely in immunocompetent hosts (1). More rare presentations include brain abscesses can be seen in patients with cerebral trauma, peritoneal infections have been shown to occur in patients undergoing multiple pericenteses, and bacteremia in patients with indwelling catheters (1). Infection with Streptomyces is not common so susceptibility data is limited. Available data shows that organisms were consistently susceptible to amikacin; frequently susceptible to imipenem, clarithromycin or erythromycin, minocycline, and trimethoprim-sulfamethoxazole; and infrequently susceptible to ciprofloxacin and ampicillin (4).

Our patient had not received the stem cell unit that this grew from, so another aliquot was requested. The second aliquot did not grow any organisms, so the Streptomyces was considered a contaminant.

References

  1. Procop, Gary W., et al. Konemans Color Atlas and Textbook of Diagnostic Microbiology. 7th ed., Wolters Kluwer Health, 2017.
  2. Tille, Patricia M. Bailey & Scotts Diagnostic Microbiology. 13th ed., Elsevier, 2014.
  3. Chater KF. Recent advances in understanding Streptomyces. F1000Res. 2016;5:2795. Published 2016 Nov 30. doi:10.12688/f1000research.9534.1
  4. Mona Kapadia, Kenneth V.I. Rolston, Xiang Y. Han, Invasive Streptomyces Infections: Six Cases and Literature Review, American Journal of Clinical Pathology, Volume 127, Issue 4, April 2007, Pages 619–624, https://doi.org/10.1309/QJEBXP0BCGR54L15

-Casey Rankins, DO, is a 3rd year Anatomic and Clinical Pathology resident at the University of Vermont Medical Center.

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

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