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Pneumocystis carinii: taxing taxonomy
1Department of Infectious Diseases, St. Jude Children's Research Hospital, Memphis, TN 38101.
European Journal of Epidemiology
|September 1, 1989
Summary
The classification of Pneumocystis carinii remains uncertain, with conflicting evidence regarding its fungal or protozoan nature. Further research is needed to definitively place this organism taxonomically.
Area of Science:
- Microbiology
- Mycology
- Parasitology
Background:
- The taxonomic classification of Pneumocystis carinii is debated, with arguments for both fungal and protozoan designations.
- Existing data present conflicting characteristics when compared to known fungi and protozoa.
Purpose of the Study:
- To review the evidence for and against the fungal or protozoan classification of Pneumocystis carinii.
- To highlight the limitations in current data and taxonomic criteria for Pneumocystis carinii.
Main Methods:
- Comparative analysis of rRNA gene sequences (16s and 18s rRNA) between P. carinii, fungi (Saccharomyces cerevisiae, Neurospora crassa), and protozoa.
- Evaluation of ultrastructural features, membrane fusion potential, and DNA content.
- Assessment of therapeutic responses to antimicrobial and antifungal agents.
Main Results:
- rRNA sequence homology data show greater similarity to fungi, while other molecular and cellular characteristics resemble protozoa.
- P. carinii exhibits therapeutic responsiveness to antiprotozoal drugs (pentamidine, trimethoprim-sulfamethoxazole, pyrimethamine-sulfadiazine) but not to common antifungal agents (amphotericin B, ketoconazole).
Conclusions:
- Current data are insufficient for a definitive taxonomic placement of Pneumocystis carinii.
- Multifactorial determinants are crucial for classification, and clear criteria, especially incorporating molecular genetics, are lacking for both protozoan and fungal classifications.