Trophic Form Research Articles

Transitional chelal digit patterns in saprophagous astigmatan mites

Changes in the functional shape of astigmatan mite moveable digit profiles are examined to test if Tyrophagus putrescentiae (Acaridae) is a trophic intermediate between a typical micro-saprophagous carpoglyphid (Carpoglyphus lactis) and a common macro-saprophagous glycyphagid (Glycyphagus domesticus). Digit tip elongation in these mites is decoupled from the basic physics of optimising moveable digit inertia. Investment in the basal ramus/coronoid process compared to that for the moveable digit mastication length varies with feeding style. A differentiated ascending ramus is indicated in C. lactis and in T. putrescentiae for different trophic reasons. Culturing affects relative investments in C. lactis. A markedly different style of feeding is inferred for the carpoglyphid. The micro-saprophagous acarid does not have an intermediate pattern of trophic functional form between the other two species. Mastication surface shape complexity confirms the acarid to be heterodontous. T. putrescentiae is a particularly variably formed species trophically. A plausible evolutionary path for the gradation of forms is illustrated. Digit form and strengthening to resist bending under occlusive loads is explored in detail. Extensions to the analytical approach are suggested to confirm the decoupling of moveable digit pattern from cheliceral and chelal adaptations. Caution is expressed when interpreting ordinations of multidimensional data in mites.

Gene expression in lung epithelial cells following interaction with Pneumocystis carinii and its specific life forms yields insights into host gene responses to infection.

Pneumocystis spp. interacts with epithelial cells in the alveolar spaces of the lung. It is thought that the binding of Pneumocystis to host cell epithelium is needed for life cycle completion and proliferation. The effect of this interaction on lung epithelial cells has previously shown that the trophic form of this organism greatly inhibits p34cdc2 activity, a serine/threonine kinase required for transition from the G2 to M phase in the cell cycle. To gain further insight into the host response during Pneumocystis pneumonia infection, we used microarray technology to profile epithelial cell (A549) gene expression patterns following Pneumocystis carinii interaction. Furthermore, we isolated separate populations of cyst and trophic forms of P. carinii, which were then applied to the lung epithelial cells. Differential expression of genes involved in various cellular functions dependent on the specific P. carinii life form in contact with the A549 cell was identified. The reliability of our data was further confirmed by Northern blot analysis on a number of selected upregulated or downregulated transcripts. The transcriptional response to P. carinii was dominated by cytokines, apoptotic, and antiapoptosis-related genes. These results reveal several previously unknown effects of P. carinii on the lung epithelial cell and provide insight into the complex interactions of host and pathogen.

The tropic life forms of Pneumocystis alter alveolar macrophage responses to inflammatory stimuli

Abstract Pneumocystis is an opportunistic fungal pathogen that causes pneumonia in immunosuppressed individuals including patients with HIV. There are two identifiable life forms of Pneumocystis including a cyst or ascus form that has a β-glucan-rich fungal cell wall and a trophic form that lacks the cell wall. In infected lungs the trophic forms can outnumber the asci by as much as 10 to 1. We have previously published that the trophic forms of Pneumocystis are able to inhibit the production of pro-inflammatory cytokines such as TNF induced by β-glucans or LPS in bone marrow-derived dendritic cells. Recently we found that trophic forms also inhibit TNF production by alveolar macrophages when stimulated in vitro. To understand relevance of this observation during Pneumocystis infection, RAG−/− mice were infected with the trophic forms of Pneumocystis, treated with an echinocandin drug to prevent the formation of ascus forms, and challenged with a low dose of LPS given intratracheally. Twenty-four hours later bronchial alveolar lavage fluids were obtained and TNF quantitated. The trophic forms of Pneumocystis significantly inhibited the production of TNF in mice challenged with LPS compared to those given LPS alone or LPS plus echinocandin. Interestingly, there was no difference in the influx of neutrophils into the lungs in LPS-treated mice compared to trophic form infected and LPS-treated mice. It is well known that TNF is an important factor in host defense against Pneumocystis while neutrophils have not been shown to enhance clearance but coincide with lung pathology. Together our data indicates that trophic forms of Pneumocystis alter selected parts of the inflammatory milieu of the lungs.

Characterization of Pneumocystis murina Bgl2, an Endo-β-1,3-Glucanase and Glucanosyltransferase.

Glucan is the major cell wall component of Pneumocystis cysts. In the current study, we have characterized Pneumocystis Bgl2 (EC 3.2.1.58), an enzyme with glucanosyltransferase and β-1,3 endoglucanase activity in other fungi. Pneumocystis murina, Pneumocystis carinii, and Pneumocystis jirovecii bgl2 complementary DNA sequences encode proteins of 437, 447, and 408 amino acids, respectively. Recombinant P. murina Bgl2 expressed in COS-1 cells demonstrated β-glucanase activity, as shown by degradation of the cell wall of Pneumocystis cysts. It also cleaved reduced laminaripentaose and transferred oligosaccharides, resulting in polymers of 6 and 7 glucan residues, demonstrating glucanosyltransferase activity. Surprisingly, confocal immunofluorescence analysis of P. murina-infected mouse lung sections using an antibody against recombinant Bgl2 showed that the native protein is localized primarily to the trophic form of Pneumocystis in both untreated mice and mice treated with caspofungin, an antifungal drug that inhibits β-1,3-glucan synthase. Thus, like other fungi, Bgl2 of Pneumocystis has both endoglucanase and glucanosyltransferase activities. Given that it is expressed primarily in trophic forms, further studies are needed to better understand its role in the biology of Pneumocystis.

Anaeramoebidae fam. nov., a Novel Lineage of Anaerobic Amoebae and Amoeboflagellates of Uncertain Phylogenetic Position

We report discovery of a new lineage of anaerobic marine amoebae and amoeboflagellates, Anaeramoeba gen. nov., represented by six newly described species. The trophic form of Anaeramoeba spp. is an amoeba corresponding to the uncommon flabellate or flamellian morphotype - it is fan-shaped and produces an anterior, flattened hyaline zone and posterior hyaline projections. In contrast to other representatives of these morphotypes, cells of Anaeramoeba spp. possess acristate mitochondrion-related organelles associated with prokaryotic symbionts, and a large acentriolar centrosome. Surprisingly, two Anaeramoeba species form morphologically unique flagellates with two or four isokont, thickened flagella. Phylogenetic analyses of the SSU rRNA gene showed that Anaeramoeba spp. form a clade, which is not robustly related to any other eukaryotic lineage. We accommodate Anaeramoeba in a new family Anaeramoebidae, which we classify as Eukaryota incertae sedis.

Observaciones parasitológicas en ratas de San José, Costa Rica

A parasitologic study is presented of 103 adult house rats from various sites in San Jose, Costa Rica. Seven specimens were Rattus rattus rattus, and the rest were Rattus norvegicus. The following protozoa were found in trophic form when feces were examined for eggs and larvae of helminths: Trichomonas, Giardia, Hexamita, Chilomastix, and Entamoeba. Trypanosoma lewisi was found in the blood of 7 out of 17 rats examined (8,8%) The following nematodes and cestodes were found with the incidence indicated: Strongyloides ratti (41,7 %); Aspiculuris tetraptera (1,9 %); Nipostron­gylus brasiliensis (47,6%); Gongylonema neoplasticum (0,9 %); Protospirura muris (8,7%); Trichosomoides crassicauda (23,3%); Taenia taeniformis larvae (33%); Hymenolepis diminuta (43,6%); and H. nana (0,9 %). No larvae of Trichinella spiralis were found in diaphragms examined. The acanthocephalian Moniliformis moniliformis was found in 18,4 per cent of the rats. Arthropods found as ectoparasites were, in arder of incidence, Echino­laelaps echidninus (14,5%), Xenopsilla cheopis (7,7 %) and Ctenopsyllus se­gnis (1,9%). These percent data should be regarded as minimum figures, as only 61 rats were brought alive to the laboratory.

The life cycle stages of the opportunistic fungal pathogen Pneumocystis murina provoke a differential immune response in antigen-presenting cells

Abstract Pneumocystis species are opportunistic fungal pathogens that cause severe pneumonia in immunocompromised hosts. The life cycle of Pneumocystis species consists of a trophic stage and an ascus-like cystic stage. Our lab has published data demonstrating that cysts stimulate NF-κB translocation in alveolar macrophages, but the trophic form does not. Here, we demonstrate that infection of wild-type adult mice with a normal mixture of trophic and cystic P. murina life forms elicits a more robust innate immune response in the alveolar spaces and lung parenchyma than infection with the trophic form alone. To determine the pattern recognition receptors that bind trophozoites and cysts, we examined expression of C-type lectin receptors on lung CD11c+ dendritic cells in vivo. Infection with a mixture of trophozoites and cysts resulted in the upregulation of dectin-1 and mannose receptor, while infection with trophozoites alone resulted in upregulation of dectin-2, DEC-205 and mannose receptor. In addition, we demonstrate that bone marrow-derived dendritic cells stimulated with a mixture of trophozoites and cysts produced the proinflammatory cytokines IL-1β and IL-6. In contrast, exposure to trophozoites suppressed β-glucan-induced IL-1β, IL-6, and TNFα production by bone marrow-derived dendritic cells. A targeted gene expression assay is being used to evaluate gene expression in dendritic cells following stimulation with trophozoites alone or a mixture of trophozoites and cysts. We propose that trophozoites suppress β-glucan-signaling, but are sufficient for stimulating protective responses in immunocompetent individuals.

The trophic stage of the opportunistic fungal pathogen Pneumocystis murina suppresses β-1,3-glucan-induced cytokine production, but is sufficient for generating protective CD4+ T cell and B cell responses (MPF2P.746)

Abstract Pneumocystis species are opportunistic fungal pathogens that cause severe pneumonia in immunocompromised hosts. The life cycle of Pneumocystis species consists of a trophic stage and ascus-like cysts. Our lab has published data demonstrating that cysts stimulate NF-κB translocation in alveolar macrophages, but the trophic form does not. Here, we demonstrate that bone marrow-derived dendritic cells pulsed with mixed P. murina express more IL-1β and induce greater CD4+ T cell interferon-γ production than bone marrow-derived dendritic cells pulsed with the trophic form alone. Additionally, our data indicate that the trophic form suppresses β-1,3-glucan-induced IL-1β production by bone marrow-derived dendritic cells. β-1,3-glucan is the predominant structural component in the cyst wall, but is not produced by the trophic form. Despite evidence of immunosuppression, our data demonstrate that the trophic form stimulates protective CD4+ T cell and B cell responses. CD4+ T cells transferred from BALB/c donor mice infected with the trophic form alone mediate clearance in RAG2KO host mice infected with either the trophic form or mixed P. murina. Infection with the trophic form generates protective B cell responses that mediate clearance following reinfection with either trophozoites or mixed P. murina. We propose that the trophic stage suppresses β-1,3-glucan-induced cytokine production, but is sufficient for stimulating protective responses in immunocompetent individuals.

Recognition of the cyst life cycle stage induces a robust immune response to the opportunistic fungal pathogen Pneumocystis murina (MPF3P.814)

Abstract Pneumocystis species are opportunistic fungal pathogens that cause severe pneumonia in immunocompromised hosts. The life cycle of Pneumocystis species consists of a vegetative trophic stage and an ascus-like cystic stage. We demonstrate that infection of wild-type adult or neonatal mice with a mixture of trophic and cystic P. murina life forms elicits a more robust CD4+ and CD8+ T cell response than infection with the trophic form alone. β-1,3-glucan is a predominant structural component in the cyst wall, but is not produced by the trophic stage. Depletion of cysts with the β-1,3-glucan synthase inhibitor anidulafungin prevents expansion of the remaining trophic organisms in immunocompromised adult mice. Depletion of cysts in immunocompetent adult mice results in fewer infiltrating CD11b+ cells in the bronchoalveolar lavage fluid. In addition, bone marrow-derived dendritic cells pulsed with mixed P. murina express more IL-1β and induce greater in vitro CD4+ T cell interferon-γ production than cells pulsed with the trophic form alone. Dendritic cells have been previously reported to activate CD4+ T cells in response to Dectin-1 stimulation by purified Pneumocystis β-1,3-glucan. We propose that dendritic cells stimulated by β-1,3-glucan on cystic Pneumocystis direct a robust pro-inflammatory response, while stimulation with the trophic form induces a less exuberant immune response that is sufficient for clearance in immunocompetent individuals.

Real-time PCR assay-based strategy for differentiation between active Pneumocystis jirovecii pneumonia and colonization in immunocompromised patients

Diagnosis of pneumocystosis usually relies on microscopic demonstration of Pneumocystis jirovecii in respiratory samples. Conventional PCR can detect low levels of P. jirovecii DNA but cannot differentiate active pneumonia from colonization. In this study, we used a new real-time quantitative PCR (qPCR) assay to identify and discriminate these entities. One hundred and sixty-three bronchoalveolar lavage fluids and 115 induced sputa were prospectively obtained from 238 consecutive immunocompromised patients presenting signs of pneumonia. Each patient was classified as having a high or a low probability of P. jirovecii pneumonia according to clinical and radiological presentation. Samples were processed by microscopy and by a qPCR assay amplifying the P. jirovecii mitochondrial large-subunit rRNA gene; qPCR results were expressed as trophic form equivalents (TFEq)/mL by reference to a standard curve obtained from numbered suspensions of trophic forms. From 21 samples obtained from 16 patients with a high probability of P. jirovecii pneumonia, 21 were positive by qPCR whereas only 16 were positive by microscopy. Fungal load ranged from 134 to 1.73 × 106 TFEq/mL. Among 257 specimens sampled from 222 patients with a low probability of P. jirovecii pneumonia, 222 were negative by both techniques but 35 were positive by qPCR (0.1–1840 TFEq/mL), suggesting P. jirovecii colonization. Two cut-off values of 120 and 1900 TFEq/mL were proposed to discriminate active pneumonia from colonization, with a grey zone between them. In conclusion, this qPCR assay discriminates active pneumonia from colonization. This is particularly relevant for patient management, especially in non-human immunodeficiency virus (HIV)-infected immunocompromised patients, who often present low-burden P. jirovecii infections that are not diagnosed microscopically.

Ploidy of Cell-Sorted Trophic and Cystic Forms of Pneumocystis carinii

Once regarded as an AIDS-defining illness, Pneumocystis pneumonia (PcP) is nowadays prevailing in immunocompromised HIV-negative individuals such as patients receiving immunosuppressive therapies or affected by primary immunodeficiency. Moreover, Pneumocystis clinical spectrum is broadening to non-severely-immunocompromised subjects who could be colonized by the fungus while remaining asymptomatic for PcP, thus being able to transmit the infection by airborne route to susceptible hosts. Although the taxonomical position of the Pneumocystis genus has been clarified, several aspects of its life cycle remain elusive such as its mode of proliferation within the alveolus or its ploidy level. As no long-term culture model exists to grow Pneumocystis organisms in vitro, an option was to use a model of immunosuppressed rat infected with Pneumocystis carinii and sort life cycle stage fractions using a high-through-put cytometer. Subsequently, ploidy levels of the P. carinii trophic and cystic form fractions were measured by flow cytometry. In the cystic form, eight contents of DNA were measured thus strengthening the fact that each mature cyst contains eight haploid spores. Following release, each spore evolves into a trophic form. The majority of the trophic form fraction was haploid in our study. Some less abundant trophic forms displayed two contents of DNA indicating that they could undergo (i) mating/fusion leading to a diploid status or (ii) asexual mitotic division or (iii) both. Even less abundant trophic forms with four contents of DNA were suggestive of mitotic divisions occurring following mating in diploid trophic forms. Of interest, was the presence of trophic forms with three contents of DNA, an unusual finding that could be related to asymmetrical mitotic divisions occurring in other fungal species to create genetic diversity at lower energetic expenses than mating. Overall, ploidy data of P. carinii life cycle stages shed new light on the complexity of its modes of proliferation.

Distribution, abundance and diversity of modern dinoflagellate cyst assemblages from southern Chile (43–54° S)

Abstract The distribution, abundance and diversity of modern dinoflagellate cyst assemblages were investigated in sediments from the inshore seas of southern Chile (43°08′–54°55′ S) at eight sites from April 2004 to January 2005. A total of 24 cyst types were recorded, of which 12 and five were identified at the species and genus levels, respectively. Dinoflagellate cysts were recorded from all sampling sites, but they differed in total abundance (15–270 cysts ml-1) and diversity index (H′ 0.88–2.40). Heterotrophic dinoflagellate cysts assigned to heterotrophic species were the most abundant trophic form, with 418 cysts ml-1, representing 55% of the total cyst abundance. Cluster analysis based on the abundance of dinoflagellate cyst species indicated that sampling sites were segregated into three groups likely to be related to the proportion of autotrophic vs. heterotrophic species cysts and the total abundance of cysts at each site. Distinctive cyst species composition differences among sampling sites may allow inferences about local nutrient and feeding dynamics within the water column.

The ste3 pheromone receptor gene of Pneumocystis carinii is surrounded by a cluster of signal transduction genes.

Although the clinical aspects of Pneumocystis carinii pneumonia are well characterized, the basic biology of the causative organism is poorly understood. Most proposed life cycles of P. carinii include both asexual and sexual replicative cycles. The two most prominent morphological forms are a trophic form, thought to undergo asexual replication by binary fission, and a cystic form or ascus containing intracystic bodies or ascospores, the products of sexual replication. To facilitate the Pneumocystis genome project, a P. carinii f. sp. carinii genomic cosmid library and an additional lambda cDNA library were generated. A partial expressed sequence tag database, created as part of the genome project, revealed the transcription of meiosis-specific genes and other genes related to sexual reproduction. The ortholog of Ste3, an a-factor pheromone receptor, was cloned and genes surrounding the ste3 locus were examined. Clustered around the ste3 gene are genes encoding elements functional in the pheromone response signal transduction cascade of model fungal organisms. These include the Ste20 protein kinase, the Ste12 homoeodomain transcriptional regulator, a potential pheromone mating factor, and other DNA-binding proteins. The genomic organization of the ste3 locus bears significant similarity to that of the mating locus recently described in Cryptococcus neoformans. The P. carinii genome contains much of the genetic machinery necessary for pheromone responsiveness, and these data support the existence of a sexual replication cycle.

Inhibition of growth of Pneumocystis carinii by lactoferrins alone and in combination with pyrimethamine, clarithromycin and minocycline.

The in vitro activity of lactoferrins alone and in combination with clarithromycin, minocycline and pyrimethamine was investigated against three clinical isolates of Pneumocystis carinii. Susceptibility was tested by inoculating isolates on to cell monolayers and determining the parasite count after 72 h incubation at 37 degrees C. The culture medium was supplemented with serial dilutions of each agent. At 20 mg/L, bovine lactoferrin, the most active agent, suppressed the growth of cystic and trophic forms by >60%. Human lactoferrin, at the same concentration, suppressed the growth of cystic and trophic forms by >50%. Lactoferrins at 20 mg/L combined with clarithromycin 4 mg/L had high anti-P. carinii activity, with a >90% decrease in cystic and trophic form counts. Our study suggests that lactoferrins may inhibit P. carinii growth in vitro and act synergically with other clinically used compounds. These findings lend experimental support to the use of iron-chelating agents in the therapy of pneumocystis infections.

Ultrastructural Morphology of Intermediate Forms and Forms Suggestive of Conjugation in the Life Cycle of Pneumocystis carinii

The intrapulmonary life cycle of Pneumocystis carinii has been proposed to include asexual reproduction of haploid trophic forms and sexual reproduction to form cysts or ascospores containing 8 intracystic bodies or spores. This study presents the ultrastructural morphology of trophic forms and developing ascospores. Nuclear-associated organelles (NAO) were observed in these various forms and in a binucleated trophozoite. The unique configuration of the nuclei and NAO in this binucleated trophic form were similar to ultrastructural features observed in conjugation of Saccharomyces cerevisiae. NAOs in developing ascospores were present in pairs and were associated with multiple nuclei. In more mature ascospores, NAO were associated with individual spores. The intermediate forms described in this study support an asexual and sexual reproductive process in P. carinii.

Use of an ATP bioluminescent assay to evaluate viability of Pneumocystis carinii from rats

A bioluminescent assay which employs the luciferin-luciferase ATP-dependent reaction was used to evaluate the viability of populations of Pneumocystis carinii derived from infected rat lungs. Contamination with host cells was reduced by a purification method which involved a combination of low- and high-speed centrifugations resulting in a 1,000-fold reduction of the rat cells while enriching for the trophic form of P. carinii. A linear correlation for the number of P. carinii nuclei versus the amount of ATP was observed. The ATP content of the organism populations could be maintained at inoculum levels for one week, although the number of organisms did not increase. Addition of respiratory chain inhibitors dramatically decreased the ATP content of the P. carinii after 24 h of incubation, with the exception of the antibiotic oligomycin B. Low concentrations of trimethoprim-sulfamethoxazole and pentamidine isethionate reduced the organism ATP content by over 50% after 24 h of exposure, while no effect was observed with 100-fold greater concentrations of ampicillin. The bioluminescent assay was found to be a more sensitive indicator of viability than a dual fluorescent staining technique. This assay does not require replication of P. carinii and should be a useful method for in vitro drug screening and viability assessment of P. carinii populations.

An anaerobic protozoon, with symbiotic methanogens, living in municipal landfill material

We have established that anaerobic protozoa do live in municipal landfill material although they probably spend much of the time encysted, especially in the drier (< 40% water) site. At least eight species were observed; they were readily isolated by adding anoxic water to dry landfill samples. The ciliate Metopus palaeformis was frequently i isolated; it appears to be ubiquitous in anaerobic landfills. It has a polymorphic life cycle, it is positive for hydrogenase, each ciliate contains about 500 bromoethanesulfonate-sensitive methanogen symbionts (probably Methanobacterium formicicum), and maximum cell densities in culture exceed 3000 per ml. The methanogens are not attached to the hydrogenosomes, neither do they undergo morphological transformation; the ciliate receives no measurable energetic advantage from its symbionts. The ciliate encysts in response to a shortage of food or water, and the methanogens remain viable within the cysts. When the protozoon excysts, the methanogens resume growth and cell division within the trophic form of the ciliate. Unlike free-living methanogens, the M. palaeformis-methanogen consortium is not particularly sensitive to oxygen; the symbiotic methanogens remain viable following exposure of the consortium to atmospheric oxygen for several days. Dispersal of methanogen-bearing protozoan cysts through oxygenated environments is a potential mechanism of transfer between landfill sites and other anaerobic environments. Anaerobic protozoan consortia are theoretically capable of making a significant contribution to methane generation from wet landfill sites.

The fine structure of Acanthamoeba astronyxis, with special emphasis on encystment.

The fine structure of the trophozoite, encysting cells, and the cyst of Acanthamoeba astronyxis has been examined. In the trophic form a microtubule organizing center was associated with a well developed Golgi complex. During encystment the organelles of the amoeba changed considerably. The profiles of rough endoplasmic reticulum elongated and were often arranged in circles of multilayered concentric systems, enclosing mitochondria, the nucleus, or other inclusions. The mitochondria showed a tendency toward elongation and constriction. One or two nucleolus-like bodies appeared in the nucleus. Lipid droplets increased considerably in amount and were distributed individually or as aggregates. The mature cyst was star-shaped and surrounded by an almost circular exocyst and an endocyst that was closely apposed to the cell membrane. Both walls differed in their thickness and granulation. The exocyst was continuous over the entire cyst, while the endocyst was interrupted by gaps, ostioles, in the region of the rays. Within the ostioles was a bell-shaped structure, the operculum. The latter was composed of a granular material comparable in electron density to that of the endocyst.

Transformation in Tetrahymena thermophila: Development of an inducible phenotype

Tetrahymena thermophila transforms from a pyriform-shaped trophic form to an elongate rapidly swimming, dispersal form under the appropriate conditions of starvation [Nelsen, E. M., and DeBault, L. E. (1978). J. Protozool. 25, 113–119] . The development and control of the dispersal phenotype are examined. After an initial starvation period, the cell replaces its oral structures. During oral replacement, a caudal cilium emerges at the posterior end of the cell. As oral replacement is completed, the cell becomes spindle shaped and the newly-formed oral membranelles are positioned beneath the surface of the cell with somatic ciliary rows exterior to them. The spindle-shaped cell then elongates to become the dispersal form. While the cell is developing the new oral structures, it is also drastically increasing its numbers of somatic basal bodies and cilia. The events in the transformation pathway may be arrested or reversed by feeding the cell, except that once oral replacement has begun, it is completed along with an associated streamlining of the cell. Refed cells revert to the normal vegetative phenotype, except that some shape changes persist for several hours, suggesting that they are compatible with, but independent of, growth. Blockage of protein synthesis with cycloheximide prevents all changes associated with transformation, including the shape changes and elongation of the caudal cilium. The relation between transformation and conjugation has also been examined. Less transformation takes place when mating is possible, but transformed cells may also mate.

Encystation of axenically grownEntamoeba histolytica: Effect of bacterial endotoxins, starch and epinephrine

Axenically grown trophozoites of Entamoeba histolytica, starch fed and toxin treated, when incubated in a minimal medium containing epinephrine and theophylline at 33° ± 1°C were transformed to a round form with a thick outer wall; in contrast, the untreated cells died. These round bodies or “precysts” hatched to the trophic form when transferred to fresh growth medium. Formation of round bodies occurred even in the absence of cysteine but they were not mature and readily disintegrated.