Final Diagnosis -- Protothecal Peritonitis


Contributors' Notes:

Prototheca species are algae that lack chlorophyll, but are closely related to the green algae chlorella. Prototheca is ubiquitous in nature and has been isolated from a wide variety of sources including sewage, soil, and many water sources, including both fresh and salt water. They are heterotrophic, requiring external sources of carbon, nitrogen, and thiamine, which they obtain from detritus and the waste products of other organisms. There remains some controversy over the taxonomic classification as Prototheca shares some important features with both alae and fungi (6).

Prototheca was first identified by Kruger in 1894 when he isolated it from the slime flux of trees (7). Over the next several decades, numerous species of Prototheca were tentatively identified. Many of these species were later shown to be the same and at this time three species are generally recognized: P. zopfii, P. wickerhamii, and P. stagnera.

Prototheca can transiently colonize the alimentary canal of both animals and humans without causing disease. When Prototheca does cause disease in animals, it is almost always P. zopfii. Protothecosis has been reported in a wide variety of animals, but most cases have been in dogs and cattle. The canine form tends to be more severe with systemic disease involving multiple internal organs and can lead to death. In bovine infections, only the udder is typically involved (1).

In humans, protothecosis is almost always caused by P. wickerhamii. Most of the reported cases have been in adults and can be divided into three major categories of disease:

  1. Simple cutaneous infections represent over half of the cases and present as discrete, indurated and painless papules, plaques, or ulcers. Systemic disease does not typically follow (8).
  2. Olecranon bursitis make up about a third of the cases and can occur following surgical procedures or after non-penetrating trauma such as falls or motor vehicle acci dents where the site of trauma later becomes contaminated.
  3. Opportunistic infections that occur in patients with cancer, on steroids or other immunosuppressive therapy.
There have been three reported cases of peritonitis in patients undergoing peritoneal dialysis. All of these patients were cured by treatment with Amphotericin B (9,10,11).

Treatment: When possible, surgical excision has been helpful. Prototheca is very sensitive to amphotericin B, apparently due to the ergosterol that makes up 4% of its membrane. For patients who cannot tolerate amphotericin, ketoconazole or fluconazole have been used. Treatment for various infections have been summarized recently by Iacovioello et al (6).


  1. Kwon-Chung, K and J Bennett. Medical Mycology. 1992. Lea & Ferbiger, Philadelphia.
  2. Klintworth, G, F. Fetter, nd H Nielsen, Jr. Protothecosis, an algal infection: report of a case in man. J Med Microbiol 1968 1:211-216.
  3. Camargo, Z, and O Fischman. Use of Morpho-physiological Characteristics for Differentiaion of the Species of Prototheca. Sabouraudia 1979 17:275-278.
  4. Sudman, M. Protothecosis: A critical review. Am J Clin Pathol 1974 61:10-19.
  5. API 20C reference
  6. Iacoviello, V, P DeGiorolami, J Lucarini, K Sutker, M Williams, and C Wanke. Protothecosis complicating prolonged endotracheal intubation: case report and literature review. Clin Inf Dis 1992 15:959-67.
  7. Kruger, W. Kurz charactistic einger niedern Organismen in Laftflusse de laublaume. I. Uber einen neuen Pilz-typus reprasentiert durch die Gattung Prototheca (Pr. moriformis et Pr. zopfii). II Ueber zwei aus Laftflussesrein gezuchtet Algen. Hewigia 1894 33:241-266.
  8. Boyd, A, M Langley, and L King, Jr.. Cutaneous manifestations of Prototheca infections. J Am Acad Dermatol 1995 32:758-64.
  9. Sands, M, D Poppel, and R Brown. Peritonitis due to Prototheca wickerhamii in a patient undergoing chronic ambulatory peritoneal dialysis. Rev Inf Dis 1991 13:376-8.
  10. O'Connor, J G Nimmo, R Rigby, F Petrie, I Hardie and R. Strong. Algal peritonitis complicating continuous ambula tory peritoneal dialysis. Am J Kid Dis 1986 8(2):122-123.
  11. Gibb A, R Aggarwal, R. Swainson. Successful treatment of Prototheca peritonitis complicating continuous ambulatory dialysis. J Infect 199122:183-5.
Contributed by Michael Torbenson, MD., John Sheaffer, MD., Robert Macauley, MD., John Anhalt, MD., PhD. and William Pascule, ScD.>

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