Contrasting microbiota profiles observed in children carrying either Blastocystis spp. or the commensal amoebas Entamoeba coli or Endolimax nana

Recent studies have shown how intestinal parasites can modulate gut microbiota. This observation is not surprising since the human intestinal lumen, like any other niche, is a battlefield of microbial competition, and Eukaryotes can affect bacterial populations. Intestinal pathogenic protist has been associated with reshaping the microbial community structure; however, the interactions between the colonic bacterial communities and parasites like Blastocystis spp., Entamoeba coli, and Endolimax nana have been poorly studied. In this work, we studied the distal intestinal bacterial microbiota of 49 children attending 7 public daycare centers in Medellin, Colombia, and compared the bacterial microbiota structure in the presence or absence of the protists Blastocystis spp., E. coli, and E. nana. Parasite colonization was associated with an increase in bacterial richness. Moreover, Blastocystis spp. presented a positive relationship with Prevotella, since this bacterium was selectively enriched in children carrying it. Remarkably, the E. coli colonized children showed a microbial profile that was closer to uninfected controls, although some bacterial taxa displayed to be enriched. This is the case for Akkermansia, which showed to be favored in E. coli colonized individuals, while notably reduced in the Blastocystis spp. parasitized group.

Occurrence and genetic identifications of porcine Entamoeba, E. suis and E. polecki, at Tangerang in West Java, Indonesia

Entamoeba suis and E. polecki subtype (ST) 1 and ST3 recently have been inferred to be virulent in pigs. However, because relevant molecular epidemiological surveys have been limited, the prevalences of these species remain unknown and their pathogenicities are still controversial. We surveyed 196 fecal samples of pigs (118 of adults, 78 of piglets) at Tangerang in West Java, Indonesia, in 2017, employing PCR using porcine Entamoeba-specific primers. E. suis was the more frequently detected species, observed in 81.1% of samples, while E. polecki ST1 and ST3 were detected in 18.4% and 17.3% of samples, respectively; mixed infections (harboring 2-3 species or subtypes of Entamoeba) were confirmed in 29.3% of positive samples. Statistically significant differences in the positive rates were not seen between adult pigs and piglets, except for those of E. polecki ST3. The prevalences of Eimeria spp. and/or Cystoisospora suis (79.1%), strongyles (55.6%), and Strongyloides spp. (6.1%) were also observed morphologically in the samples. Further chronological or seasonal investigations of pigs and humans in these high-prevalence areas are needed to assess the virulence of the Entamoeba parasites, including the effects on pig productivity, and to evaluate the zoonotic impacts of these organisms.

Invasive Colonic Entamoebiasis in Wild Cane Toads, Australia

We detected a disease syndrome in free-ranging Australian cane toads involving atypical behavior and emaciation that is associated with a previously undescribed Entamoeba sp. that infiltrates the colonic lining, causing it to slough. The organism may become seasonally pathogenic when toads are under hydric and nutritional stress.

[CHARACTERISTICS OF PARASITIC PROTOZOA METABOLISM AND POSSIBILITIES OF ANTIPROTOZOA DRUG DEVELOPMENT (REVIEW)]

One of the most poorly studied areas of protozoology is metabolic processes of parasitic protozoa. Study of the biochemistry of parasites required for the development of effective chemotherapy of protozoal diseases. Some amitochondrial parasites of humans, such as Giardia intestinalis, Entamoeba histolytica, Trichomonas sp., living in an environment with low oxygen content, have specialized cellular organelles-hydrogenosomes (like mitochondria provide cells with simple energy). The study of the functioning of these organelles allows us to consider them as targets for the development of аntiprotozoal drugs. The target for chemotherapy in the treatment of trypanosomiasis can be processes related to the characteristics of the glycolytic pathway or a decrease in the level of energy substrate, such as glucose. This leads to a rapid decrease in ATP levels in the cell of the parasite, an overall loss of mobility and disappearance of trypanosomes from the bloodstream of the infected host. Also, glucose transporters located in the membrane of the parasite can be targets for drugs.

Characteristics of inflammatory reactions during development of liver abscess in hamsters inoculated with Entamoeba nuttalli

Background

Entamoeba nuttalli is an intestinal protozoan with pathogenic potential that can cause amebic liver abscess. It is highly prevalent in wild and captive macaques. Recently, cysts were detected in a caretaker of nonhuman primates in a zoo, indicating that E. nuttalli may be a zoonotic pathogen. Therefore, it is important to evaluate the pathogenicity of E. nuttalli in detail and in comparison with that of E. histolytica.

Methodology/Principal findings

Trophozoites of E. nuttalli GY4 and E. histolytica SAW755 strains were inoculated into liver of hamsters. Expression levels of proinflammatory factors of hamsters and virulence factors from E. histolytica and E. nuttalli were compared between the two parasites. Inoculations with trophozoites of E. nuttalli resulted in an average necrotic area of 24% in liver tissue in 7 days, whereas this area produced by E. histolytica was nearly 50%. Along with the mild liver tissue damage induced by E. nuttalli, expression levels of proinflammatory factors (TNF-α, IL-6 and IL-1β) and amebic virulence protein genes (lectins, cysteine proteases and amoeba pores) in local tissues were lower with E. nuttalli in comparison with E. histolytica. In addition, M2 type macrophages were increased in E. nuttalli-induced amebic liver abscesses in the late stage of disease progression and lysate of E. nuttalli trophozoites induced higher arginase expression than E. histolytica in vitro.

Conclusions/Significance

The results show that differential secretion of amebic virulence proteins during E. nuttalli infection triggered lower levels of secretion of various cytokines and had an impact on polarization of macrophages towards a M1/M2 balance. However, regardless of the degree of macrophage polarization, there is unambiguous evidence of an intense acute inflammatory reaction in liver of hamsters after infection by both Entamoeba species.

Entamoeba nuttalli is the phylogenetically closest protozoan to Entamoeba histolytica and is highly prevalent in macaques. Previous studies have indicated that E. nuttalli is virulent in a hamster model. In this study, we compared the immunopathological basis of formation of liver abscess in hamsters between E. nuttalli and E. histolytica. Mild liver tissue damage developed after intrahepatic injection of trophozoites of E. nuttalli, and lower expression levels of genes for host proinflammatory factors and amebic virulence proteins were detected at the edges of liver abscesses induced by E. nuttalli. In addition, alternatively activated macrophages were increased in E. nuttalli-induced liver abscesses in the late stage of disease progression. The lysate of E. nuttalli trophozoites also induced higher arginase expression than E. histolytica in vitro. Polarization of macrophages is likely to affect the degree of acute inflammatory reactions in liver in an animal model during E. nuttalli infection. Our data reveal new characteristics of abscess formation by E. nuttalli.

Differential expression of pathogenic genes of Entamoeba histolytica vs E. dispar in a model of infection using human liver tissue explants

We sought to establish an ex vivo model for examining the interaction of E. histolytica with human tissue, using precision-cut liver slices (PCLS) from donated organs. E. histolytica- or E. dispar-infected PCLS were analyzed at different post-infection times (0, 1, 3, 24 and 48 h) to evaluate the relation between tissue damage and the expression of genes associated with three factors: a) parasite survival (peroxiredoxin, superoxide dismutase and 70 kDa heat shock protein), b) parasite virulence (EhGal/GalNAc lectin, amoebapore, cysteine proteases and calreticulin), and c) the host inflammatory response (various cytokines). Unlike E. dispar (non-pathogenic), E. histolytica produced some damage to the structure of hepatic parenchyma. Overall, greater expression of virulence genes existed in E. histolytica-infected versus E. dispar-infected tissue. Accordingly, there was an increased expression of EhGal/GalNAc lectin, Ehap-a and Ehcp-5, Ehcp-2, ehcp-1 genes with E. histolytica, and a decreased or lack of expression of Ehcp-2, and Ehap-a genes with E. dispar. E. histolytica-infected tissue also exhibited an elevated expression of genes linked to survival, principally peroxiredoxin, superoxide dismutase and Ehhsp-70. Moreover, E. histolytica-infected tissue showed an overexpression of some genes encoding for pro-inflammatory interleukins (ILs), such as il-8, ifn-γ and tnf-α. Contrarily, E. dispar-infected tissue displayed higher levels of il-10, the gene for the corresponding anti-inflammatory cytokine. Additionally, other genes were investigated that are important in the host-parasite relationship, including those encoding for the 20 kDa heat shock protein (HSP-20), the AIG-1 protein, and immune dominant variable surface antigen, as well as for proteins apparently involved in mechanisms for the protection of the trophozoites in different environments (e.g., thioredoxin-reductase, oxido-reductase, and 9 hypothetical proteins). Some of the hypothetical proteins evidenced interesting overexpression rates, however we should wait to their characterization. This finding suggest that the present model could be advantageous for exploring the complex interaction between trophozoites and hepatocytes during the development of ALA, particularly in the initial stages of infection.

The ecological catastrophe of oral diseases: a possible link between periodontitis and protozoa

Periodontal disease (PD) is one of the prevalent diseases in the adult population. The ethiology of PD has never been completely understood, however, loss of balance between the host immune system and the microbial virulence of PD pathogens may be considered the trigger of PD. In fact, the immune system, activated by microbiological agents, attacks the host and not the biofilm bacteria, causing the destruction of periodontal tissue, alveolar bone and loss of teeth. Parasites may play an important role in the pathology of PD. The first studied and the most common parasite in the oral cavity is Entamoeba gingivalis. A possible link between E. gingivalis and PD has never been demonstrated completely, however E. gingivalis is infrequently found in people without PD. In addition, there is evidence that E. gingivalis could favour the onset and progression of PD. In conclusion, we can assert that E. gingivalis and PD may be correlated. This relationship can open new therapeutical approaches for treating PD, particularly in cases refractory to therapy.

Variation in Rural African Gut Microbiota Is Strongly Correlated with Colonization by Entamoeba and Subsistence

The human gut microbiota is impacted by host nutrition and health status and therefore represents a potentially adaptive phenotype influenced by metabolic and immune constraints. Previous studies contrasting rural populations in developing countries to urban industrialized ones have shown that industrialization is strongly correlated with patterns in human gut microbiota; however, we know little about the relative contribution of factors such as climate, diet, medicine, hygiene practices, host genetics, and parasitism. Here, we focus on fine-scale comparisons of African rural populations in order to (i) contrast the gut microbiota of populations inhabiting similar environments but having different traditional subsistence modes and either shared or distinct genetic ancestry, and (ii) examine the relationship between gut parasites and bacterial communities. Characterizing the fecal microbiota of Pygmy hunter-gatherers as well as Bantu individuals from both farming and fishing populations in Southwest Cameroon, we found that the gut parasite Entamoeba is significantly correlated with microbiome composition and diversity. We show that across populations, colonization by this protozoa can be predicted with 79% accuracy based on the composition of an individual's gut microbiota, and that several of the taxa most important for distinguishing Entamoeba absence or presence are signature taxa for autoimmune disorders. We also found gut communities to vary significantly with subsistence mode, notably with some taxa previously shown to be enriched in other hunter-gatherers groups (in Tanzania and Peru) also discriminating hunter-gatherers from neighboring farming or fishing populations in Cameroon.

Species-specific immunity induced by infection with Entamoeba histolytica and Entamoeba moshkovskii in mice

Entamoeba histolytica, the parasitic amoeba responsible for amoebiasis, causes approximately 100,000 deaths every year. There is currently no vaccine against this parasite. We have previously shown that intracecal inoculation of E. histolytica trophozoites leads to chronic and non-healing cecitis in mice. Entamoeba moshkovskii, a closely related amoeba, also causes diarrhea and other intestinal disorders in this model. Here, we investigated the effect of infection followed by drug-cure of these species on the induction of immunity against homologous or heterologous species challenge. Mice were infected with E. histolytica or E. moshkovskii and treated with metronidazole 14 days later. Re-challenge with E. histolytica or E. moshkovskii was conducted seven or 28 days following confirmation of the clearance of amoebae, and the degree of protection compared to non-exposed control mice was evaluated. We show that primary infection with these amoebae induces a species-specific immune response which protects against challenge with the homologous, but not a heterologous species. These findings pave the way, therefore, for the identification of novel amoebae antigens that may become the targets of vaccines and provide a useful platform to investigate host protective immunity to Entamoeba infections.

Transcriptome analysis of encystation in Entamoeba invadens

Encystation is an essential differentiation process for the completion of the life cycle of a group of intestinal protozoa including Entamoeba histolytica, the causative agent of intestinal and extraintestinal amebiasis. However, regulation of gene expression during encystation is poorly understood. To comprehensively understand the process at the molecular level, the transcriptomic profiles of E. invadens, which is a related reptilian species that causes an invasive disease similar to that of E. histolytica, was investigated during encystation. Using a custom-generated Affymetrix platform microarray, we performed time course (0.5, 2, 8, 24, 48, and 120 h) gene expression analysis of encysting E. invadens. ANOVA analysis revealed that a total of 1,528 genes showed ≥3 fold up-regulation at one or more time points, relative to the trophozoite stage. Of these modulated genes, 8% (116 genes) were up-regulated at the early time points (0.5, 2 and 8h), while 63% (962 genes) were up-regulated at the later time points (24, 48, and 120 h). Twenty nine percent (450 genes) are either up-regulated at 2 to 5 time points or constitutively up-regulated in both early and late stages. Among the up-regulated genes are the genes encoding transporters, cytoskeletal proteins, proteins involved in vesicular trafficking (small GTPases), Myb transcription factors, cysteine proteases, components of the proteasome, and enzymes for chitin biosynthesis. This study represents the first kinetic analysis of gene expression during differentiation from the invasive trophozoite to the dormant, infective cyst stage in Entamoeba. Functional analysis on individual genes and their encoded products that are modulated during encystation may lead to the discovery of targets for the development of new chemotherapeutics that interfere with stage conversion of the parasite.

Enteric protozoa in the developed world: a public health perspective

Several enteric protozoa cause severe morbidity and mortality in both humans and animals worldwide. In developed settings, enteric protozoa are often ignored as a cause of diarrheal illness due to better hygiene conditions, and as such, very little effort is used toward laboratory diagnosis. Although these protozoa contribute to the high burden of infectious diseases, estimates of their true prevalence are sometimes affected by the lack of sensitive diagnostic techniques to detect them in clinical and environmental specimens. Despite recent advances in the epidemiology, molecular biology, and treatment of protozoan illnesses, gaps in knowledge still exist, requiring further research. There is evidence that climate-related changes will contribute to their burden due to displacement of ecosystems and human and animal populations, increases in atmospheric temperature, flooding and other environmental conditions suitable for transmission, and the need for the reuse of alternative water sources to meet growing population needs. This review discusses the common enteric protozoa from a public health perspective, highlighting their epidemiology, modes of transmission, prevention, and control. It also discusses the potential impact of climate changes on their epidemiology and the issues surrounding waterborne transmission and suggests a multidisciplinary approach to their prevention and control.

Determining the prevalence of intestinal parasites in three Orang Asli (Aborigines) communities in Perak, Malaysia

This study was conducted to determine the prevalence of intestinal parasites among children and adult Orang Aslis (Aborigines) from different locations in Perak. Faecal samples were collected and analyzed using the direct smear and formal ether sedimentation technique. Some of the faecal samples were stained using the Modified Acid fast stain for Cryptosporidium. Nail clippings of the respondents and the soil around their habitat were also analyzed. Of the 77 stool samples examined, 39 (50.6%) were positive for at least one intestinal parasite. The most common parasite detected was Trichuris trichiura (39.0%) followed by Ascaris lumbricoides (26.9%), Entamoeba coli (5.2%), Giardia lamblia (5.2%), Blastocystis hominis (3.9%), hookworm (3.9%), Entamoeba histolytica (1.3%), Iodamoeba butschlii (1.3%) and Cryptosporidium sp. (1.3%) respectively. Some respondents had single parasites (24.7%), some with two parasites (18.2%). Some with three parasites (6.5%) and one had four parasites species (1.3%). The parasites were slightly more common in females (54.7%) than males ((41.7%). The parasites were more common in the 13-20 year age group (90.9%) followed by 1-12 years (69.6%), 21-40 year age group (34.8%) and least in the 41-60 year age group (27.8%). Nail examinations of the respondents did not show any evidence of parasites. One had a mite, three had pollen grains and one had yeast cells isolated from the finger nails. Soil samples taken around their houses showed only one sample with a nematode ova and one with oocyst which was of a non human origin.

Proteomic comparison of Entamoeba histolytica and Entamoeba dispar and the role of E. histolytica alcohol dehydrogenase 3 in virulence

The protozoan intestinal parasite Entamoeba histolytica infects millions of people worldwide and is capable of causing amebic dysentery and amebic liver abscess. The closely related species Entamoeba dispar colonizes many more individuals, but this organism does not induce disease. To identify molecular differences between these two organisms that may account for their differential ability to cause disease in humans, we used two-dimensional gel-based (DIGE) proteomic analysis to compare whole cell lysates of E. histolytica and E. dispar. We observed 141 spots expressed at a substantially (>5-fold) higher level in E. histolytica HM-1∶IMSS than E. dispar and 189 spots showing the opposite pattern. Strikingly, 3 of 4 proteins consistently identified as different at a greater than 5-fold level between E. histolytica HM-1∶IMSS and E. dispar were identical to proteins recently identified as differentially expressed between E. histolytica HM-1∶IMSS and the reduced virulence strain E. histolytica Rahman. One of these was E. histolytica alcohol dehydrogenase 3 (EhADH3). We found that E. histolytica possesses a higher level of NADP-dependent alcohol dehydrogenase activity than E. dispar and that some EhADH3 can be localized to the surface of E. histolytica. Episomal overexpression of EhADH3 in E. histolytica trophozoites resulted in only subtle phenotypic differences in E. histolytica virulence in animal models of amebic colitis and amebic liver abscess, making it difficult to directly link EhADH3 levels to virulence differences between E. histolytica and less-pathogenic Entamoeba.

Infection with Entamoeba histolytica can result in disabling diarrhea or even death, while the morphologically identical and genetically similar Entamoeba dispar harmlessly colonizes the human intestine. Understanding the molecular differences between these two organisms by comparing their protein repertoire may help us to understand why E. histolytica invades into colonic tissue, while E. dispar remains a benign passenger. Here, we identify four proteins that appear to be differentially expressed between the two species and show that a metabolic enzyme, which would appear to be an unlikely candidate for a role in disease, is expressed at much higher levels in the pathogenic organism.

Comparison of the proteome profiles of Entamoeba histolytica and its close but non-pathogenic relative Entamoeba dispar

The microaerophilic protist Entamoeba histolytica is a source of considerable morbidity and mortality in many countries of the world by acting as a causative agent of amoebic dysentery and liver abscess. Its close relative, Entamoeba dispar, also colonises the human colon but is non-pathogenic. In the present study, we wanted to assess if the close relatedness of these two organisms could be used to identify virulence factors in E. histolytica through a comparison of the protein expression profiles of the pathogenic and the non-pathogenic species. We applied two-dimensional polyacrylamide gel electrophoresis in order to identify proteins which are specifically expressed in E. histolytica and which therefore could constitute candidate proteins potentially involved in E. histolytica pathogenicity. The evaluation of overall protein expression profiles derived from whole cell extracts, however, revealed that, in spite of the close relatedness at the genetic level, the disparity of the proteomic profiles of these two Entamoeba species is far too great in order to pinpoint proteins whose expression might render E. histolytica pathogenic. Taken together, our study performed at the proteomic level clearly supports the notion of E. histolytica and E. dispar as two distinct species.

An Entamoeba sp. strain isolated from rhesus monkey is virulent but genetically different from Entamoeba histolytica☆

An Entamoeba sp. strain, P19-061405, was isolated from a rhesus monkey in Nepal and characterized genetically. The strain was initially identified as Entamoeba histolytica using PCR amplification of peroxiredoxin genes. However, sequence analysis of the 18S rRNA gene showed a 0.8% difference when compared to the reference E. histolytica HM-1:IMSS human strain. Differences were also observed in the 5.8S rRNA gene and the internal transcribed spacer (ITS) regions 1 and 2, and analysis of the serine-rich protein gene from the monkey strain showed unique codon usages compared to E. histolytica isolated from humans. The amino acid sequences of two hexokinases and two glucose phosphate isomerases also differed from those of E. histolytica. Isoenzyme analyses of these enzymes in the monkey strain showed different electrophoretic mobility patterns compared with E. histolytica isolates. Analysis of peroxiredoxin genes indicated the presence of at least seven different types of protein, none of which were identical to proteins in E. histolytica. When the trophozoites from the monkey strain were inoculated into the livers of hamsters, formation of amebic abscesses was observed 7 days after the injection. These results demonstrate that the strain is genetically different from E. histolytica and is virulent. Revival of the name Entamoeba nuttalli is proposed for the organism.

Pathogenicity of Entamoeba dispar under xenic and monoxenic cultivation compared to a virulent E. histolytica

Two xenic isolates and cloned cultures of Entamoeba dispar were submitted to monoxenization using Crithidia fasciculata as the associated organism. Growth in monoxenic cultivation and ability of xenic and monoxenic trophozoites to destroy VERO cells and produce lesions in hamster livers were compared to those of a virulent E. histolytica. Parental and cloned E. dispar under monoxenic cultivation showed a remarkable lower growth than the monoxenic E. histolytica and were avirulent in both in vivo and in vitro tests. When xenically cultured, trophozoites of E. dispar showed a moderate lytic activity against VERO cells (1.5 to 41.8% of destruction) but caused severe hepatic lesions in hamsters as those caused by the virulent E. histolytica (29 to 100% in prevalence and 0.86 to 4.00 in lesion degree). Although E. dispar has not been associated with invasive disease in men, the ability of xenic trophozoites to produce prominent tissue damage in experimental conditions has indicated that some strains have a considerable pathogenic potential when in presence of bacteria.

Comparative genomic hybridizations of Entamoeba strains reveal unique genetic fingerprints that correlate with virulence

Variable phenotypes have been identified for Entamoeba species. Entamoeba histolytica is invasive and causes colitis and liver abscesses but only in approximately 10% of infected individuals; 90% remain asymptomatically colonized. Entamoeba dispar, a closely related species, is avirulent. To determine the extent of genetic diversity among Entamoeba isolates and potential genotype-phenotype correlations, we have developed an E. histolytica genomic DNA microarray and used it to genotype strains of E. histolytica and E. dispar. On the basis of the identification of divergent genetic loci, all strains had unique genetic fingerprints. Comparison of divergent genetic regions allowed us to distinguish between E. histolytica and E. dispar, identify novel genetic regions usable for strain and species typing, and identify a number of genes restricted to virulent strains. Among the four E. histolytica strains, a strain with attenuated virulence was the most divergent and phylogenetically distinct strain, raising the intriguing possibility that genetic subtypes of E. histolytica may be partially responsible for the observed variability in clinical outcomes. This microarray-based genotyping assay can readily be applied to the study of E. histolytica clinical isolates to determine genetic diversity and potential genotypic-phenotypic associations.

Entamoeba histolytica and/or Entamoeba dispar: infection frequency in HIV+/AIDS patients in Mexico city

The objective of this work was to evaluate the frequency of Entamoeba histolytica/Entamoeba dispar intestinal infection in HIV+/AIDS subjects and their HIV- close relatives or sexual partners. Enteric parasites were investigated in stool samples by microscopic examination and E. histolytica and E. dispar were identified by PCR. We found by microscopic analysis in HIV+/AIDS group that the E. histolytica/E. dispar complex was present in 5.9% of the members, while in the HIV- group was 2.9%. With PCR we found that the E. histolytica prevalence was 25.3% in the HIV+/AIDS group and 18.5% in the HIV-group. The difference in the results obtained with the microscopic and PCR is due to the different sensibility of the procedures. Besides, we found patients who were infected with E. histolytica in both groups were asymptomatic cyst passers. Our results suggest that E. histolytica strains prevalent in the studied community appear to be of low pathogenic potential.

Entamoeba histolytica and Entamoeba dispar utilize externalized phosphatidylserine for recognition and phagocytosis of erythrocytes

Amebic erythrophagocytosis is characteristic of invasive amebiasis, and mutants deficient in erythrocyte ingestion are avirulent. We sought to understand the molecular mechanisms underlying erythrocyte phagocytosis by Entamoeba histolytica. Following adherence to amebae, erythrocytes became round and crenulated, and phosphatidylserine (PS) was exposed on their outer membrane leaflets. These changes were similar to the effects of calcium treatment on erythrocytes, which we utilized to separate ameba-induced exposure of erythrocyte PS from the process of phagocytosis. The adherence and phagocytosis of calcium-treated erythrocytes were less inhibited by galactose than were those of healthy erythrocytes, suggesting the existence of an amebic coreceptor specific for PS. To test whether PS was recognized by amebae, calcium-treated cells were incubated with annexin V prior to adherence to or ingestion by E. histolytica. Annexin V blocked both adherence (50% +/- 12% inhibition; P < 0.05) and phagocytosis (65% +/- 10%; P < 0.05), providing evidence that at least one galactose-independent coreceptor was involved in the adherence and ingestion of red blood cells. The coreceptor was inhibited by phospho-l-serine and to a lesser extent by phospho-d-serine but not by phospho-l-threonine, which is consistent with the coreceptor functioning in the adherence and ingestion of erythrocytes via recognition of PS. We expanded our investigations to the highly related but noninvasive parasite Entamoeba dispar and demonstrated that it was deficient in red-blood-cell adherence, induction of PS exposure, and phagocytosis. These findings establish phosphatidylserine involvement in erythrophagocytosis by amebae and suggest the existence of a PS receptor on the surfaces of both E. histolytica and E. dispar.

[Entamoeba histolytica and Entamoeba dispar: differentiation methods and implications]

Entamoeba histolytica and Entamoeba dispar are two species morphologically identical (except hematophagous trophozoites) but one of them is pathogenic. Sensitive and specific molecular techniques which are able to distinguish E. histolytica from E. dispar have been developed recently. Detection of antigen in stool using the ELISA method is the diagnostic test method of choice for clinical use in the developing world. It is rapid and simple. Cultures for zymodeme analysis and PCR detection of the parasite remain research tools. Species identification is imperative both for improved clinical diagnosis and treatment and for planning control strategies.

[Experimental study on the pathogenesis of Entamoeba gingivalis]

OBJECTIVE

To study the pathogenesis of Entamoeba gingivalis (E. g.) and its relation to periodontal diseases.

METHODS

Rats were treated with immuno-inhibitor for one week and the neck of incisor teeth of the rats was bound with steel wire. They were randomly divided into three groups: the first group was infected by E. g. in the periodontal tissue, the second group was infected by symbiotic bacteria (s. b.), and the third group was given physiological saline as control. Observation on the periodontal inflammation was made for each group of rats, and the purulent secretion from periodontal abscess was examined for living pathogens.

RESULTS

The incidence of periodontal diseases in rats infected by E. g. was higher than that of symbiotic bacteria group and that of control (P < 0.05), the incidence of periodontal diseases in rats infected by s. b. was higher than that of control group (P < 0.05). Living pathogens were found in the abscess liquid.

CONCLUSION

E. g. is an opportunistic pathogen, which, together with synergistic symbiotic bacteria, can cause periodontal diseases in hosts with low immunity.

Induction of permeability changes and death of vertebrate cells is modulated by the virulence of Entamoeba spp. isolates

Although Entamoeba histolytica is capable of inducing an apoptotic response in vertebrate cells in vitro (Cell. Microbiol. 2 (2000) 617), it is not known whether vertebrate cell death requires direct amoeba-vertebrate cell contact or simply the presence of amoebae in the area of the vertebrate cells. In addition, Entamoeba spp. vary in their virulence and pathogenicity. The potential effects of these critical parameters also have not been elucidated. We tested the virulent HM-1:IMSS isolate and the non-virulent Rahman isolate of E. histolytica, and the non-virulent E. dispar CYNO16:TPC isolate against two vertebrate cell lines, HeLa and Chinese hamster ovary cells in vitro using ethidium homodimer as a fluorescent indicator of changes in vertebrate cell permeability. Fluorescence appeared in vertebrate cell nuclei within approximately 2-3 min of contact between HM-1 amoebae and vertebrate cells independent of vertebrate cell type. However, vertebrate cells in the immediate vicinity of but not contacted by HM-1 amoebae were not affected. In contrast, although both E. histolytica Rahman and E. dispar CYNO16 amoebae moved freely among and contacted vertebrate cells, the nuclei of the vertebrate cells never fluoresced implying that the cells remained alive and impermeant to the ethidium homodimer. This is the first demonstration that direct contact between virulent amoebae and vertebrate cells is required to kill vertebrate cells and that the process is restricted to virulent Entamoeba isolates. An understanding at the molecular level of the processes involved could help to reduce the pathology associated with this parasite.

The abundant polyadenylated transcript 2 DNA sequence of the pathogenic protozoan parasite Entamoeba histolytica represents a nonautonomous non-long-terminal-repeat retrotransposon-like element which is absent in the closely related nonpathogenic species Entamoeba dispar

While comparing gene expression in the pathogenic organism Entamoeba histolytica and the closely related but nonpathogenic species Entamoeba dispar, we discovered that the E. histolytica abundant polyadenylated transcript 2 (ehapt2) and corresponding genomic copies are absent in E. dispar. Although polyadenylated, ehapt2 does not contain any overt open reading frame. Southern blot and sequence analyses revealed that about 500 copies of ehapt2 genomic elements were present in each cell and that the copies were distributed throughout the ameba genome. The various ehapt2 elements are regularly located in the vicinity of protein-encoding genes, downstream of pyrimidine-rich sequence stretches (40 to 125 bp; CT content, 79.2 to 85.5%), and are flanked by duplicated target sites of variable length. Target site duplications were obviously generated during integration of ehapt2 into the E. histolytica genome as one copy of the flanking repeat and the complete ehapt2 element are specifically absent in orthologous E. dispar genomic sequences. ehapt2 shares 3' sequences with EhRLE, a recently identified non-long-terminal-repeat (non-LTR) retrotransposon-like element of E. histolytica, which contains a conceptual open reading frame for reverse transcriptase. Thus, ehapt2 has all of the properties of nonautonomous non-LTR retrotransposons. A comparison of various E. histolytica isolates suggested that transposition of ehapt2 takes place at a very low frequency as the genomic localization of ehapt2 elements was found to be well conserved. A mobile element such as ehapt2 could be a suitable mechanism to explain the infrequent and late transition of E. histolytica from a harmless gut commensal to an invasive pathogen.

Biological aspects of a Brazilian strain of Entamoeba dispar

A strain of Entamoeba dispar was characterized by clinical diagnosis, serological and electrophoretical isoenzyme analysis and by the polymorphism of a 482 bp genomic fragment analysis. The pathogenesis and virulence of this strain was investigated considering the experimental infection in hamster livers in association with the original intestinal microbiota. Liver lesions were observed in hamsters experimentally infected with trophozoites from xenic cultures, but not from the monoxenic cultures. Moreover, clones obtained from re-isolated strain Wil1R1 showed a distinct biological behavior. In fact, animals inoculated with Wil1R1ClB3 showed an intense acute inflammatory reaction with destructive focal hepatic lesions. These lesions were characterized as amebic abscesses. The association between bacteria and ameba has been fairly well studied because it affects the pathogenicity of the amebas and has important therapeutic implications. In this study, we demonstrated that E. dispar in association with the original microbiota is able to produce lesions in hamster liver in spite of its having been considered to be non-pathogenic in the hamster model. Based on these results we suggest that diagnosis of amebiasis needs to be made with more care and that clinical and therapeutical procedures need to be revised.

Protozoon infections and intestinal permeability

Intestinal permeability (IP) studies using some macromolecules have been assumed to demonstrate the intactness of intestinal mucosa. The aim of the present study is to determine the changes in IP among patients with protozoan infections. Thirty nine patients with protozoan infections and ten healthy controls were enrolled in the study. Protozoa were diagnosed by Native-lugol, Richie and Trichrome staining of faeces. IP was evaluated by diethyl triamine penta acetic acid labeled with 99m Technetium (99mTc labeled DTPA) assay. The IP was found to have increased in patients with protozoan infections compared with control patients (7.20+/-5.52 vs. 4.47+/-0.65%, P=0.0017). The IP values were 9.91+/-10.05% in Giardia intestinalis group, 6.81+/-2.25% in Blastocystis hominis group, 5.78+/-2.84% in Entamoeba coli group. In comparison with the control group, the IP was significantly higher in G. intestinalis and B. hominis patients (P=0.0025, P=0.00037, respectively), but not in E. coli patients. In conclusion, the IP increases in patients with G. intestinalis and B. hominis but not with E. coli infection. This finding supports the view that IP increases during the course of protozoan infections which cause damage to the intestinal wall while non-pathogenic protozoan infections have no effect on IP. The increase in IP in patients with B. hominis brings forth the idea that B. hominis can be a pathogenic protozoan.

Clinical significance of the redefinition of the agent of amoebiasis

Entamoeba histolytica is the pathogenic species of Entamoeba that causes amoebic dysentery and other invasive disease. The morphologically similar species, E. dispar, is non-pathogenic and accounts for about 90% of the previously estimated 500 million E. histolytica infections world-wide. Because of the recent redefinition of E. histolytica and E. dispar, and the limited number of drugs available to treat amoebiasis, a new approach to treatment of individuals carrying these parasites is necessary. A meeting of eminent scientists has recently agreed that on no account should prophylaxis against amoebiasis be given, and no treatment without symptoms should be administered. The expense of treating asymptomatic individuals, both monetary and at the risk of over-use of precious drugs, does not appear to be justified. It would seem wise that we preserve currently effective anti-amoebic drugs and avoid the development of drug-resistant E. histolytica.

Overexpression of cysteine proteinase 2 in Entamoeba histolytica or Entamoeba dispar increases amoeba-induced monolayer destruction in vitro but does not augment amoebic liver abscess formation in gerbils

To study the role of cysteine proteinases in the pathogenicity of Entamoeba histolytica, we have attempted to overexpress the three main cysteine proteinases (EhCP1, EhCP2, EhCP5) of this parasite in trophozoites of E. histolytica as well as in non-pathogenic Entamoeba dispar by episomal transfection. Although each of the corresponding coding sequences were cloned in identical expression plasmids, we were unable to overexpress EhCP1 and EhCP5, respectively, but could substantially induce expression of EhCP2 in both amoeba species by sevenfold, leading to a threefold increase in total cysteine proteinase activity. Overexpression of EhCP2 did not influence expression of other cysteine proteinases and could be attributed to an increase of a single 35 kDa activity band in substrate gel electrophoresis. In contrast to previous findings, which indicated that amoeba cysteine proteinases are involved in erythrophagocytosis and liver abscess formation, cells overexpressing EhCP2 showed no difference in erythrophagocytosis or liver abscess formation compared with respective controls. However, overexpression of EhCP2 in both amoeba species resulted in a marked increase of in vitro monolayer destruction.

Recent developments in amoebiasis:the Gal/GalNAc lectins of Entamoeba histolytica and Entamoeba dispar

Amoebiasis is responsible for 50000-100000 deaths annually. Invasive amoebic disease begins with the attachment of Entamoeba histolytica trophozoites to colonic mucin, a process mediated by the amoebic Gal/GalNAc lectin. The non-pathogenic counterpart, E. dispar, is morphologically identical but genetically distinct. Investigations comparing the Gal/GalNac lectin from these two organisms are under way.

The most abundant glycoprotein of amebic cyst walls (Jacob) is a lectin with five Cys-rich, chitin-binding domains

The infectious stage of amebae is the chitin-walled cyst, which is resistant to stomach acids. In this study an extraordinarily abundant, encystation-specific glycoprotein (Jacob) was identified on two-dimensional protein gels of cyst walls purified from Entamoeba invadens. Jacob, which was acidic and had an apparent molecular mass of approximately 100 kDa, contained sugars that bound to concanavalin A and ricin. The jacob gene encoded a 45-kDa protein with a ladder-like series of five Cys-rich domains. These Cys-rich domains were reminiscent of but not homologous to the Cys-rich chitin-binding domains of insect chitinases and peritrophic matrix proteins that surround the food bolus in the insect gut. Jacob bound purified chitin and chitin remaining in sodium dodecyl sulfate-treated cyst walls. Conversely, the E. histolytica plasma membrane Gal/GalNAc lectin bound sugars of intact cyst walls and purified Jacob. In the presence of galactose, E. invadens formed wall-less cysts, which were quadranucleate and contained Jacob and chitinase (another encystation-specific protein) in secretory vesicles. A galactose lectin was found to be present on the surface of wall-less cysts, which phagocytosed bacteria and mucin-coated beads. These results suggest that the E. invadens cyst wall forms when the plasma membrane galactose lectin binds sugars on Jacob, which in turn binds chitin via its five chitin-binding domains.

Cysteine proteinases and the pathogenesis of amebiasis

Amebiasis is a major cause of morbidity and mortality throughout the tropical world. Entamoeba histolytica is now recognized as a separate species from the morphologically identical E. dispar, which cannot invade. Cysteine proteinases are a key virulence factor of E. histolytica and play a role in intestinal invasion by degrading the extracellular matrix and circumventing the host immune response through cleavage of secretory immunoglobulin A (sIgA), IgG, and activation of complement. Cysteine proteinases are encoded by at least seven genes, several of which are found in E. histolytica but not E. dispar. A number of new animal models, including the formation of liver abscesses in SCID mice and intestinal infection in human intestinal xenografts, have proven useful to confirm the critical role of cysteine proteinases in invasion. Detailed structural analysis of cysteine proteinases should provide further insights into their biochemical function and may facilitate the design of specific inhibitors which could be used as potential chemotherapeutic agents in the future.

[Studies on the continuous culture and pathogenicity of Entamoeba gingivalis]

OBJECTIVE

To establish a method for continuous culture of Entamoeba gingivalis (E. g.) and study the pathogenicity of E. g..

METHODS

The culture conditions of E. g. were compared by observing its growth and reproduction. The pathogenicity of E. g. was studied by investigating its infection rate in humans and observing the relationship between E. g. infection and periodontal abscess in rats and the in vitro effect of some drugs.

RESULTS

The optimal culture condition of E. g. was modified LES medium containing Locke's solution with 20% bovine serum, penicillin, streptomycin and rice starch. Reproduction of E. g. peaked at the fourth day of incubatoin, E. g. could live continuously for 120 to 168 h. The infection rate of E. g. was higher in patients with periondontal diseases than in healthy groups. The animal test showed that E. g. could cause periondontal abscess in rats. The levels of acid phosphatase and MDA were higher in patients with E. g.-positive periondontal disease than in healthy individuals. Metronidazole and SBF are effective against E. g..

CONCLUSION

E. g. could grow very well in modified LES medium, and cause periondontal abscess in patients with low immunity.

Absence of lipophosphoglycan-like glycoconjugates in Entamoeba dispar

Invasive amoebiasis is the result of infection of Entamoeba histolytica. The closely related Entamoeba dispar can colonize the human gut but does not cause invasive disease. In this study, E. dispar was analysed for the presence of the lipophosphoglycan-like (LPG) glycoconjugate known to be present on the cell surface of E. histolytica. E. dispar cells were radio-isotope labelled with [3H]galactose or [3H]inositol. The acidic glycoconjugates were extracted and analysed by hydrophobic chromatography over phenyl-Sepharose and by sodium dodecyl sulphate polyacrylamide gel electrophoresis. No LPG-like molecules could be identified in E. dispar in contrast to E. histolytica, suggesting that these molecules may be absent in the non-pathogenic species.

Pore-forming peptides of Entamoeba dispar. Similarity and divergence to amoebapores in structure, expression and activity

Amoebapore, a 77-residue peptide with pore-forming activity from the human pathogen Entamoeba histolytica, is implicated in the killing of phagocytosed bacteria and in the cytolytic reaction of the amoeba against host cells. Previously, we structurally and functionally characterized three amoebapore isoforms in E. histolytica but recognized only one homolog in the closely related but non-pathogenic species Entamoeba dispar. Here, we identified two novel amoebapore homologs from E. dispar by molecular cloning. Despite strong resemblance of the primary structures of the homologs, molecular modeling predicts a species-specific variance between the peptide structures. Parallel isolation from trophozoite extracts of the two species revealed a lower amount of pore-forming peptides in E. dispar and substantially higher activity of the major isoform from E. histolytica towards natural membranes than that from E. dispar. Differences in abundance and activity of the lytic polypeptides may have an impact on the pathogenicity of amoebae.

Molecular mechanisms of pathogenesis in amebiasis

Though both Entamoeba histolytica and E. dispar colonize the human gut, only the former is capable of invading tissues and causing disease. Although the biology of the parasite and the mechanism of pathogenesis have been intensively studied, there is a lack of consensus about the molecules of E. histolytica that actively participate in pathogenesis. This article reviews some key molecules involved. Ga1NAc-inhibitable adhesin is a membrane-associated glycoprotein nature, consisting of heavy and light subunits; each of these is encoded by multiple genes. The heavy subunit is useful in differentiating E. histolytica from E. dispar. Three structurally similar isoforms of amebapore, A, B and C, have been identified in E. histolytica but C is absent in E. dispar. Proteolytic enzymes such as collagenase and cysteine proteinases and cytolytic enzymes like phospholipase A are important. Collagenase activity is mainly accumulated in electron-dense granules. Cysteine proteinase is encoded by six genes, of which EhCP5 is exclusively present in E. histolytica.

Royal Society of Tropical Medicine and Hygiene Meeting at Manson House, London, 19 February 1998. Amoebic disease. Entamoeba histolytica and E. dispar: comparison of molecules considered important for host tissue destruction

Entamoeba histolytica and E. dispar are genetically distinct but closely related protozoan species. Both colonize the human gut but only E. histolytica is able to invade tissues and cause disease. Comparison of the 2 species may help to elucidate the specific mechanisms involved in the pathogenicity of E. histolytica. During the last few years, various amoeba molecules considered to be important for pathogenic tissue invasion have been identified and characterized, such as a galactose-inhibitable surface lectin, pore-forming peptides and cysteine proteinases. This review summarizes present knowledge about the structure and function of these molecules, with emphasis on the differences between E. histolytica and E. dispar.

Entamoeba dispar: ultrastructure, surface properties and cytopathic effect

The cytological features of Entamoeba dispar, recently recognized by biochemical and molecular biology criteria as a distinct species, were compared to those of Entamoeba histolytica When cultured under axenic conditions, living trophozoites of E. dispar strain SAW 76ORR clone A were more elongated in form, had a single frontal pseudopodium, and showed a noticeable uroid. In sections of E. dispar trophozoites stained with Toluidine blue, characteristic areas of cytoplasmic metachromasia were seen due to the presence of large deposits of glycogen, seldom found in E. histolytica strain HM1:IMSS. Under the light microscope the periphery of the nucleus in E. dispar was, lined by finer, more regularly distributed dense granules. With transmission electron microscopy the surface coat of E. dispar was noticeable thinner. In addition. E. dispar had a lower sensitivity to agglutinate with concanavalin A and a higher negative surface charge, measured by cellular microelectrophoresis. The cytopathic effect of E. dispar was much slower, analyzed by the gradual loss of transmural electrical resistance of MDCK epithelial cell monolayers mounted in Ussing chambers. Whereas in E. histolytica phagocytosis of epithelial cells plays an important role in its cytopathic effect. E. dispar trophozoites placed in contact with MDCK cells showed only rare evidence of phagocytosis. The results demonstrate that the morphology of E. dispar is different to that of E. histolytica, both at the light microscopical and the ultrastructural levels. In addition they show that E. dispar in axenic culture has a moderate cytopathic effect on epithelia] cell monoLayers. However, when compared to E. histolytica, the in vitro lytic capacity of E. dispar is much slower and less intense.

Differentiation of pathogenic and non-pathogenic Entamoeba: has the question been answered?

Pathogenic and non-pathogenic Entamoeba have been separated into two distinct species. Recently, the non-pathogenic E. dispar has been cultivated axenically. However, the genetic variability among different clones from the same strain, experimental production of hybrid clones which may differ from their parents, and the possibility of invasiveness of E. dispar, are some phenomena which may indicate that the last word on distinctiveness of the species has not yet been said.

Virulent and avirulent Entamoeba histolytica and E. dispar differ in their cell surface phosphorylated glycolipids

Virulent strains of Entamoeba histolytica have been reported to produce a mixture of phosphoglycoconjugates that share some structural features with the lipophosphoglycans (LPGs) of Leishmania. Purification of these glycoconjugates is essential to their precise structural characterization. In this study we have extracted 'LPG-like' molecules from various virulent E. histolytica strains and purified on the basis of charge differences, 2 apparently related glycoconjugates a 'LPG' and a 'lipophosphopeptidoglycan (LPPG)'. In marked contrast to the abundance of these 'LPG' and 'LPPG' molecules in the virulent strains, avirulent E. histolytica and E. dispar strains produce either very low, or no detectable levels of LPG, and either low levels or modified forms of 'LPPG'. Monospecific polyclonal antibodies prepared against that 'LPG' of the virulent strain HM-1:1MSS c16 identified epitopes shared between both the 'LPG' and the 'LPPG' of this and other virulent strains, using Western blot analysis. Flow cytometric analysis of a range of strains using these antibodies identified a surface distribution of these molecules and confirmed a correlation between surface exposure of epitopes bound by these antibodies and parasite virulence.

A homologue of the cysteine proteinase gene (ACP1 or Eh-CPp3) of pathogenic Entamoeba histolytica is present in non-pathogenic E. dispar strains

One of the three cysteine proteinase genes, ACP1 (or CP 3), has been reported to be missing in non-pathogenic strains of Entamoeba histolytica (or Entamoeba dispar as recently labeled). Unexpectedly, a gene fragment very similar in its sequence (95% homology) to ACP1 of pathogenic strains was obtained by use of the polymerase chain reaction from genomic DNA and cDNA of various cloned non-pathogenic strains as well as in 23 clinical isolates from asymptomatic carriers. The finding of the ACP1 homologue in non-pathogenic or E. dispar strains rules out the proposed use of its absence for diagnostic purposes.