Host-Parasite interactions in Entamoeba histolytica and Entamoeba dispar: what have we learned from their genomes?

Apocynin, an NADPH Oxidase Enzyme Inhibitor, Prevents Amebic Liver Abscess in Hamster

Amebiasis is an intestinal infection caused by Entamoeba histolytica. Amebic liver abscess (ALA) is the most common extraintestinal complication of amebiasis. In animal models of ALA, neutrophils have been shown to be the first cells to come into contact with Entamoeba histolytica during the initial phase of ALA. One of the multiple mechanisms by which neutrophils exhibit amebicidal activity is through reactive oxygen species (ROS) and the enzyme NADPH oxidase (NOX2), which generates and transports electrons to subsequently reduce molecular oxygen into superoxide anion. Previous reports have shown that ROS release in the susceptible animal species (hamster) is mainly stimulated by the pathogen, in turn provoking such an exacerbated inflammatory reaction that it is unable to be controlled and results in the death of the animal model. Apocynin is a natural inhibitor of NADPH oxidase. No information is available on the role of NOX in the evolution of ALA in the hamster, a susceptible model. Our study showed that administration of a selective NADPH oxidase 2 (NOX2) enzyme inhibitor significantly decreases the percentage of ALA, the size of inflammatory foci, the number of neutrophils, and NOX activity indicated by the reduction in superoxide anion (O2-) production. Moreover, in vitro, the apocynin damages amoebae. Our results showed that apocynin administration induces a decrease in the activity of NOX that could favor a decrease in ALA progression.

Gut Microbiota Crosstalk with Resident Macrophages and Their Role in Invasive Amebic Colitis and Giardiasis-Review

The innate immune response is highly dependent on the action of macrophages. They are abundant in the intestine subepithelial lamina propria of the mucosa, where they deploy multiple tasks and play a critical role. The balance between the gut microbiota and M2 macrophages is critical for gut health and homeostasis. Gut microbiota has the power to change macrophage phenotype and replenish the resident macrophage niche during and post infection. As far as the extracellular enteric parasitic infections invasive amebic colitis and giardiasis are concerned, a change of macrophages phenotype to a pro-inflammatory state is dependent on direct contact of the protozoan parasites with host cells. Macrophages induce strong pro-inflammatory response by inflammasome activation and secretion of interleukin IL-1β. Inflammasomes play a key role in the response to cellular stress and microbe attacks. The balance between gut mucosal homeostasis and infection is dependent on the crosstalk between microbiota and resident macrophages. Parasitic infections involve NLRP1 and NLRP3 inflammasome activation. For Entamoeba histolytica and Giardia duodenalis infections, inflammasome NLRP3 activation is crucial to promote the host defenses. More studies are needed to further elucidate possible therapeutic and protective strategies against these protozoan enteric parasites' invasive infections in humans.

Diversity and Plasticity of Virulent Characteristics of Entamoeba histolytica

The complexity of clinical syndromes of amebiasis, caused by the parasite Entamoeba histolytica, stems from the intricate interplay between the host immune system, the virulence of the invading parasite, and the surrounding environment. Although there is still a relative paucity of information about the precise relationship between virulence factors and the pathogenesis of Entamoeba histolytica, by accumulating data from clinical and basic research, researchers have identified essential pathogenic factors that play a critical role in the pathogenesis of amebiasis, providing important insights into disease development through animal models. Moreover, the parasite's genetic variability has been associated with differences in virulence and disease outcomes, making it important to fully understand the epidemiology and pathogenesis of amebiasis. Deciphering the true mechanism of disease progression in humans caused by this parasite is made more difficult through its ability to demonstrate both genomic and pathological plasticity. The objective of this article is to underscore the heterogeneous nature of disease states and the malleable virulence characteristics in experimental models, while also identifying persistent scientific issues that need to be addressed.

Distinct Phenotypic Variation of Blastocystis sp. ST3 from Urban and Orang Asli Population—An Influential Consideration during Sample Collection in Surveys

Simple Summary

Blastocystis sp. is a common intestinal protozoan of humans with the phenotypic characteristics strongly associated with its activity, including pathogenicity. This characteristic varies, but the variation has not been clearly understood. The present study evaluates the variation when a single subtype of Blastocystis sp. was isolated from a population with distinct gut microbial composition, namely, the urban and orang asli(indigenous) population. Blastocystis sp. cells isolated from orang asli individuals had a higher growth rate with elevated resistance to harsh conditions. Distinct surface coats with amoebic forms were noticed in parasite cells from urban individuals. Proteases, commonly a virulent factor in other parasites, showed variation depending on the isolation source. Stimulation of cancer cell proliferation by only Blastocystis sp. isolated from urban individuals is suggestive of the variation at the antigenic level. This phenotypic variation suggests that implicating subtype to pathogenicity may be too early, and a deeper understanding of Blastocystis sp. and microenvironment interaction is essential.

Abstract

Blastocystis sp. is a globally distributed protozoan parasite with uncertain pathogenicity. Phenotypic variation in Blastocystis sp. suggests its adaptation; however, the phenotypic features of Blastocystis sp. ST3 from a distinct source of isolation is unknown. Blastocystis sp. isolated from individuals in urban and orang asli (indigenous population in Selangor, Malaysia) settlements were studied for phenotypic characteristics such as growth profile, morphology, ultrastructure, and resistance to harsh conditions. Subsequently, pathogenic potentials, such as in protease activity and the ability to stimulate the proliferation of cancer cells, were assessed. Higher parasite counts with granular and apoptotic forms were found in Blastocystis sp. from orang asli individuals. Cells with fuzzy coats and amoebic structures which seemingly implicate increased interaction with bacteria were seen predominantly in urban symptomatic persons. Also, Blastocystis sp. from orang asli isolates resisted harsh environments, suggesting longer co-adaptation to the hosts. Urban and orang asli symptomatic isolates possessed a predominance of only cysteine protease, whereas all the asymptomatic isolates showed significantly higher cysteine, serine, or aspartic protease activity. However, only solubilized antigen from urban symptomatic isolates showed significant stimulation of cancer cell proliferation. For the first time, our findings demonstrate significant phenotypic variation in a single subtype, ST3 of Blastocystis sp., isolated from urban and orang asli populations that are known to have distinct gut microbial compositions. The outcome emphasizes the importance of identifying people’s locations and lifestyles during sample collection before forming conclusions on the prevailing data and implicating subtypes to pathogenicity. The environment plays a significant role in Blastocystis sp. infection.

Protein Phosphatase PP2C Identification in Entamoeba spp

Entamoeba histolytica is the causative agent of amoebiasis, and Entamoeba dispar is its noninvasive morphological twin. Entamoeba invadens is a reptilian parasite. In the present study, Western blot, phosphatase activity, immunofluorescence, and bioinformatic analyses were used to identify PP2C phosphatases of E. histolytica, E. dispar, and E. invadens. PP2C was identified in trophozoites of all Entamoeba species and cysts of E. invadens. Immunoblotting using a Leishmania mexicana anti-PP2C antibody recognized a 45.2 kDa PP2C in all species. In E. histolytica and E. invadens, a high molecular weight element PP2C at 75 kDa was recognized, mainly in cysts of E. invadens. Immunofluorescence demonstrated the presence of PP2C in membrane and vesicular structures in the cytosol of all species analyzed. The ~75 kDa PP2C of Entamoeba spp. shows the conserved domain characteristic of phosphatase enzymes (according to in silico analysis). Possible PP2C participation in the encystation process was discussed.

Analysis of Human Gut Microbiota Composition Associated to the Presence of Commensal and Pathogen Microorganisms in Côte d'Ivoire

Background: The human gut microbiota is a microbial ecosystem contributing to the maintenance of host health with functions related to immune and metabolic aspects. Relations between microbiota and enteric pathogens in sub-Saharan Africa are scarcely investigated. The present study explored gut microbiota composition associated to the presence of common enteric pathogens and commensal microorganisms, e.g., Blastocystis and Entamoeba species, in children and adults from semi-urban and non-urban localities in Côte d’Ivoire. Methods: Seventy-six stool samples were analyzed for microbiota composition by 16S rRDNA sequencing. The presence of adeno-, entero-, parechoviruses, bacterial and protozoal pathogens, Blastocystis, and commensal Entamoeba species, was analyzed by different molecular assays. Results: Twelve individuals resulted negative for any tested microorganisms, 64 subjects were positive for one or more microorganisms. Adenovirus, enterovirus, enterotoxigenic Escherichia coli (ETEC), and Blastocystis were frequently detected. Conclusions: The bacterial composition driven by Prevotellaceae and Ruminococcaceae confirmed the biotype related to the traditional dietary and cooking practices in low-income countries. Clear separation in UniFrac distance in subjects co-harboring Entamoeba hartmanni and Blastocystis was evidenced. Alpha diversity variation in negative control group versus only Blastocystis positive suggested its possible regulatory contribution on intestinal microbiota. Pathogenic bacteria and virus did not affect the positive outcome of co-harbored Blastocystis.

Acetylcholine Upregulates Entamoeba histolytica Virulence Factors, Enhancing Parasite Pathogenicity in Experimental Liver Amebiasis

Entamoeba histolytica is an invasive enteric protozoan, whose infections are associated to high morbidity and mortality rates. However, only less than 10% of infected patients develop invasive amebiasis. The ability of E. histolytica to adapt to the intestinal microenvironment could be determinant in triggering pathogenic behavior. Indeed, during chronic inflammation, the vagus nerve limits the immune response through the anti-inflammatory reflex, which includes acetylcholine (ACh) as one of the predominant neurotransmitters at the infection site. Consequently, the response of E. histolytica trophozoites to ACh could be implicated in the establishment of invasive disease. The aim of this study was to evaluate the effect of ACh on E. histolytica virulence. Methods include binding detection of ACh to plasma membrane, quantification of the relative expression of virulence factors by RT-PCR and western blot, evaluation of the effect of ACh in different cellular processes related to E. histolytica pathogenesis, and assessment of the capability of E. histolytica to migrate and form hepatic abscesses in hamsters. Results demonstrated that E. histolytica trophozoites bind ACh on their membrane and show a clear increase of the expression of virulence factors, that were upregulated upon stimulation with the neurotransmitter. ACh treatment increased the expression of L220, Gal/GalNAc lectin heavy subunit (170 kDa), amebapore C, cysteine proteinase 2 (ehcp-a2), and cysteine proteinase 5 (ehcp-a5). Moreover, erythrophagocytosis, cytotoxicity, and actin cytoskeleton remodeling were augmented after ACh treatment. Likewise, by assessing the formation of amebic liver abscess, we found that stimulated trophozoites to develop greater hamster hepatic lesions with multiple granulomas. In conclusion, ACh enhanced parasite pathogenicity by upregulating diverse virulence factors, thereby contributing to disease severity, and could be linked to the establishment of invasive amebiasis.

Genome-wide and structural analysis of the Myb-SHAQKYF family in Entamoeba histolytica

Amoebiasis is the third leading cause of death among protozoon parasitic diseases in the lower-middle income countries. Understanding the molecular events that control gene expression such as transcription factors, their DNA binding mode and target sequences can help to develop new antiamoebic drugs against Entamoeba histolytica. In this paper we performed a genome and structural analysis of a specific transcription factor. The genome of E. histolytica codifies for 9 EhMybSHAQKYF proteins, which are a family within a large group of 34 Myb-DNA-binding domain (Myb-DBD) containing proteins. Here we compared Entamoeba Myb-SHAQKYF proteins with Myb-like proteins from the Reveille (RVE) family, important regulators of plant circadian networks. This comparison could lead to stablish their role in E. histolytica life cycle. We show that the ehmybshaqkyf genes are differentially expressed in trophozoites under basal cell culture conditions. An in-silico analysis predicts that members of this group harbor a highly conserved and structured Myb-DBD and a large portion of intrinsically disordered residues. As the Myb-DBD of these proteins harbors a distinctive Q[VI]R[ST]HAQK[YF]F sequence in its putative third α-helix, we consider relevant to determine the three-dimensional (3D) structure of one of them. An NMR structure of the Myb-DBD of EhMybS3 shows that this protein is composed of three α-helices stabilized by a hydrophobic core, similar to Myb proteins of different kingdoms. It is remarkable that despite not sharing similarities in their amino acid sequences, the structure of the Myb-DBD of the EhMybS3 is well conserved in this early branching eukaryote.

The Entamoeba lysine and glutamic acid rich protein (KERP1) virulence factor gene is present in the genomes of Entamoeba nuttalli, Entamoeba dispar and Entamoeba moshkovskii

The lysine and glutamic acid rich protein KERP1 is a cell surface-expressed virulence factor in the human pathogen Entamoeba histolytica. It was originally suggested that the gene was absent from the related, avirulent human commensal Entamoeba dispar, an absence which would be relevant to the differential virulence of these species. Here, the gene is shown to be present in E. dispar, and its sequence is presented, as well as in a virulent parasite of macaques, Entamoeba nuttalli, and the primarily free living, opportunistically parasitic Entamoeba moshkovskii.

Entamoeba histolytica and Entamoeba dispar: Morphological and Behavioral Differences Induced by Fibronectin through GTPases Activation and Actin-Binding Proteins

Early steps of tissue invasion by Entamoeba histolytica are mediated by adhesion and migration through matrix components such as fibronectin with the participation of the actin cytoskeleton. Striking differences in their produced structures, movement, and migration were found. These observations suggest differential changes in their ability to organize the actin cytoskeleton and, therefore, to modify its morphology after adhesion to fibronectin. To understand these observations, we explore deeper the cytoskeleton pathway of E. histolytica compared to Entamoeba dispar, analyzing the activation and involvement of actin cytoskeleton regulatory proteins such as small GTPases (Rho, Rac1 and Cdc42), myosin IB, paxillin, alpha-actinin, and ARP2/3 during interaction with fibronectin. Results showed a higher activation of Rac1 in E. histolytica compared to E. dispar, while Cdc42 and RhoA were equally activated in both amebae; besides, variations in the amount of myosin IB, paxillin, and ARP2/3 were detected among these species, coinciding and reflected in formation of lamellipodia in E. histolytica and filopodia in E. dispar. These could partially explain the higher invasive capacity of E. histolytica compared to E. dispar, due to its pleomorphic ability, high motility, migration, activation, and abundance of proteins involved in the cytoskeleton arrangement.

Entamoeba histolytica infections in wild and semi-wild orangutans in Sumatra and Kalimantan

Key to the success of orangutan conservation management practices is the prevention of the introduction of infectious diseases to the remaining populations. Previous reports of Entamoeba spp. positive orangutans are of concern as Entamoeba spp. infection has been linked to morbidity and mortality in primates. It remains to be determined if the Entamoeba species infecting orangutans is the pathogenic Entamoeba histolytica. Orangutan fecal samples have been collected from orangutans from sites in Sumatra (Bukit Lawang, Ketambe, and Suaq, 241 samples from 64 individuals), and two sites in Kalimantan (Sebangau and Tuanan, 129 samples from 39 individuals). All samples were from wild orangutans except for a proportion from Sumatra which were from semi-wild (108 samples, 10 individuals). E. histolytica-specific nested PCR assays were carried out on the fecal samples. A total of 36 samples from 17 individuals tested positive for E. histolytica. When compared with published sequences using NCBI BLAST the E. histolytica positive samples showed a 98-99% concordance. The majority (76%, n = 36) of the positive isolates came from semi-wild orangutans in Bukit Lawang. This study supports the growing body of evidence that contact with humans is an important risk factor for infection of wild primates with E. histolytica.

mRNA Polyadenylation Machineries in Intestinal Protozoan Parasites

In humans, mRNA polyadenylation involves the participation of about 20 factors in four main complexes that recognize specific RNA sequences. Notably, CFIm25, CPSF73, and PAP have essential roles for poly(A) site selection, mRNA cleavage, and adenosine residues polymerization. Besides the relevance of polyadenylation for gene expression, information is scarce in intestinal protozoan parasites that threaten human health. To better understand polyadenylation in Entamoeba histolytica, Giardia lamblia, and Cryptosporidium parvum, which represent leading causes of diarrhea worldwide, genomes were screened for orthologs of human factors. Results showed that Entamoeba histolytica and C. parvum have 16 and 12 proteins out of the 19 human proteins used as queries, respectively, while G. lamblia seems to have the smallest polyadenylation machinery with only six factors. Remarkably, CPSF30, CPSF73, CstF77, PABP2, and PAP, which were found in all parasites, could represent the core polyadenylation machinery. Multiple genes were detected for several proteins in Entamoeba, while gene redundancy is lower in Giardia and Cryptosporidium. Congruently with their relevance in the polyadenylation process, CPSF73 and PAP are present in all parasites, and CFIm25 is only missing in Giardia. They conserve the functional domains and predicted folding of human proteins, suggesting they may have the same roles in polyadenylation.

Genetic Diversity and Gene Family Expansions in Members of the Genus Entamoeba

Amoebiasis is the third-most common cause of mortality worldwide from a parasitic disease. Although the primary etiological agent of amoebiasis is the obligate human parasite Entamoeba histolytica, other members of the genus Entamoeba can infect humans and may be pathogenic. Here, we present the first annotated reference genome for Entamoeba moshkovskii, a species that has been associated with human infections, and compare the genomes of E. moshkovskii, E. histolytica, the human commensal Entamoeba dispar, and the nonhuman pathogen Entamoeba invadens. Gene clustering and phylogenetic analyses show differences in expansion and contraction of families of proteins associated with host or bacterial interactions. They intimate the importance to parasitic Entamoeba species of surface-bound proteins involved in adhesion to extracellular membranes, such as the Gal/GalNAc lectin and members of the BspA and Ariel1 families. Furthermore, E. dispar is the only one of the four species to lack a functional copy of the key virulence factor cysteine protease CP-A5, whereas the gene's presence in E. moshkovskii is consistent with the species' potentially pathogenic nature. Entamoeba moshkovskii was found to be more diverse than E. histolytica across all sequence classes. The former is ∼200 times more diverse than latter, with the four E. moshkovskii strains tested having a most recent common ancestor nearly 500 times more ancient than the tested E. histolytica strains. A four-haplotype test indicates that these E. moshkovskii strains are not the same species and should be regarded as a species complex.

Pathogenic Entamoeba histolytica, but not Entamoeba dispar, induce neutrophil extracellular trap (NET) formation

Amoebiasis is an infection of global importance, caused by the eukaryotic parasite Entamoeba histolytica. Pathogenic E. histolytica is associated worldwide with over a million cases of amoebic dysentery, colitis, and amoebic liver abscess. In contrast, the nonpathogenic Entamoeba dispar does not cause these diseases, although it is commonly found in the same areas as pathogenic amoeba. Entamoeba histolytica infection is usually associated with infiltrating neutrophils. These neutrophils appear to play a defensive role against this parasite, by mechanisms not completely understood. Recently, our group reported that neutrophil extracellular traps (NET) are produced in response to E. histolytica trophozoites. But, there is no information on whether nonpathogenic E. dispar can also induce NET formation. In this report, we explored the possibility that E. dispar leads to NET formation. Neutrophils were stimulated by E. histolytica trophozoites or by E. dispar trophozoites, and NET formation was assessed by video microscopy. NET induced by E. histolytica were important for trapping and killing amoebas. In contrast, E. dispar did not induce NET formation in any condition. Also E. dispar did not induce neutrophil degranulation or reactive oxygen species production. In addition, E. histolytica-induced NET formation required alive amoebas and it was inhibited by galactose, N-acetylgalactosamine, and lactose. These data show that only alive pathogenic E. histolytica activates neutrophils to produce NET, and suggest that recognition of the parasite involves a carbohydrate with an axial HO- group at carbon 4 of a hexose.

Host-antibody inductivity of virulent Entamoeba histolytica and non-virulent Entamoeba moshkovskii in a mouse model

Background

Despite similarities in morphology, gene and protein profiles, Entamoeba histolytica and E. moshkovskii show profound differences in pathogenicity. Entamoeba histolytica infection might result in amoebic dysentery and liver abscess, while E. moshkovskii causes only mild diarrhea. Extensive studies focus on roles of host immune responses to the pathogenic E. histolytica; however, evidence for E. moshkovskii remains scarce.

Methods

To study differences in host-antibody response profiles between E. histolytica and E. moshkovskii, mice were immunized intraperitoneally with different sets of Entamoeba trophozoites as single species, mixed species and combinations.

Results

Mice prime-immunized with E. histolytica and E. moshkovskii combination, followed by individual species, exhibited higher IgG level than the single species immunization. Mice immunized with E. moshkovskii induced significantly higher levels and long-lasting antibody responses than those challenged with E. histolytica alone. Interestingly, E. histolytica-specific anti-sera promoted the cytopathic ability of E. histolytica toward Chinese hamster ovarian (CHO) cells, but showed no effect on cell adhesion. There was no significant effect of immunized sera on cytopathic activity and adhesion of E. moshkovskii toward both CHO and human epithelial human colonic (Caco-2) cell lines. Monoclonal-antibody (mAb) characterization demonstrated that 89% of E. histolytica-specific mAbs produced from mice targeted cytoplasmic and cytoskeletal proteins, whereas 73% of E. moshkovskii-specific mAbs targeted plasma membrane proteins.

Conclusions

The present findings suggest that infection with mixed Entamoeba species or E. moshkovskii effectively induces an antibody response in mice. It also sheds light on roles of host antibody response in the pathogenic difference of E. histolytica and E. moshkovskii trophozoites, and cell surface protein modifications of the amoebic parasites to escape from host immune system.

Antiamoebic drugs for treating amoebic colitis

BACKGROUND

Infection with the protozoan Entamoeba histolytica is common in low- and middle-income countries, and up to 100,000 people with severe disease die every year. Adequate therapy for amoebic colitis is necessary to reduce illness, prevent development of complicated disease and extraintestinal spread, and decrease transmission.

OBJECTIVES

To evaluate antiamoebic drugs for treating amoebic colitis.

SEARCH METHODS

We searched the available literature up to 22 March 2018. We searched the Cochrane Infectious Diseases Group Specialised Register, CENTRAL, MEDLINE, Embase, LILACS, mRCT, and conference proceedings. We contacted individual researchers, organizations, and pharmaceutical companies, and we checked reference lists.

SELECTION CRITERIA

Randomized controlled trials of antiamoebic drugs given alone or in combination, compared with placebo or another antiamoebic drug, for treating adults and children with a diagnosis of amoebic colitis.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed the eligibility and methodological quality of trials and extracted and analysed the data. We calculated clinical and parasitological failure rates and rates of relapse and adverse events as risk ratios (RRs) with 95% confidence intervals (CIs), using a random-effects model. We determined statistical heterogeneity and explored possible sources of heterogeneity using subgroup analyses. We carried out sensitivity analysis by using trial quality to assess the robustness of reported results.

MAIN RESULTS

In total, 41 trials (4999 participants) met the inclusion criteria of this review. In this update, we added four trials to the 37 trials included in the first published review version. Thirty trials were published over 20 years ago. Only one trial used adequate methods of randomization and allocation concealment, was blinded, and analysed all randomized participants. Only one trial used an E histolytica stool antigen test, and two trials used amoebic culture.Tinidazole may be more effective than metronidazole for reducing clinical failure (RR 0.28, 95% CI 0.15 to 0.51; 477 participants, eight trials; low-certainty evidence) and is probably associated with fewer adverse events (RR 0.65, 95% CI 0.46 to 0.92; 477 participants, 8 trials; moderate-certainty evidence). Compared with metronidazole, combination therapy may result in fewer parasitological failures (RR 0.36, 95% CI 0.15 to 0.86; 720 participants, 3 trials; low-certainty evidence), but we are uncertain which combination is more effective than another. Evidence is insufficient to allow conclusions regarding the efficacy of other antiamoebic drugs.

AUTHORS' CONCLUSIONS

Compared with metronidazole, tinidazole may be more effective in reducing clinical failure and may be associated with fewer adverse events. Combination drug therapy may be more effective for reducing parasitological failure compared with metronidazole alone. However, these results are based mostly on small trials conducted over 20 years ago with a variety of poorly defined outcomes. Tests that detect E histolytica more accurately are needed, particularly in countries where concomitant infection with other bacteria and parasites is common.

Entamoeba histolytica infection in humans, chimpanzees and baboons in the Greater Gombe Ecosystem, Tanzania

Entamoeba histolytica is an enteric parasite that infects approximately 50 million people worldwide. Although E. histolytica is a zoonotic parasite that has the potential to infect nonhuman primates, such transmission is poorly understood. Consequently, this study examined whether E. histolytica is present among humans, chimpanzees and baboons living in the Greater Gombe Ecosystem (GGE), Tanzania. The primary aims were to determine patterns of E. histolytica infection in a system with human-nonhuman primate overlap and to test associations between infection status and potential risk factors of disease. Entamoeba spp. occurred in 60.3% of human, 65.6% of chimpanzee and 88.6% of baboon samples. Entamoeba histolytica occurred in 12.1% of human, 34.1% of chimpanzee and 10.9% of baboon samples. Human E. histolytica infection was associated with gastrointestinal symptoms. This was the first study to confirm the presence of E. histolytica in the GGE. The high sample prevalence of E. histolytica in three sympatric primates suggests that zoonotic transmission is possible and stresses the need for further phylogenetic studies. Interventions targeting better sanitation and hygiene practices for humans living in the GGE can help prevent E. histolytica infection in humans, while also protecting the endangered chimpanzees and other primates in this region.

Correlation of genetic diversity between hosts and parasites in Entamoeba nuttalli isolates from Tibetan and rhesus macaques in China

Entamoeba nuttalli infection is prevalent in captive and wild macaques. Recent studies have suggested that genotypes of E. nuttalli isolates are correlated with the geographical distribution of host macaques. Correlation of amoebic genotypes with genetic diversity of host macaques was analyzed in present study. Sixty fresh stool samples were obtained from wild Tibetan macaques living in Mount Huang (HS) of the An-hui Province in China. PCR analysis revealed that the most prevalent Entamoeba species was E. chattoni (E. polecki ST2) (86.7%) followed by E. nuttalli (58.3%) and E. coli (25%). Six E. nuttalli HS isolates were successfully cultured. The tRNA-linked short tandem repeat (STR) loci and serine-rich protein gene of E. nuttalli isolates from four different regions of China (Mount Long-hu, Gui-yang, Mount E-mei, and HS, the former three isolates were obtained in previous studies) were studied and high numbers of polymorphisms were detected. When genetic diversity of different populations of E. nuttalli isolates was compared with geographical distance, an r² value of 0.919 was assigned by a Mantel test based on the tRNA-STR loci. In host macaques, the mtDNA HVS-I gene was also highly polymorphic in each of the genomes. Multiple regression analysis using E. nuttalli tRNA-STR loci genetic, macaque mtDNA HVS-I gene, and geographic distances showed an r² value of 0.943, indicating that a higher relevance was demonstrated when geographic and host gene factors were considered. Analysis of genetic factor of host would benefit for better understanding of the evolution of E. nuttalli.

The Sole DNA Ligase in Entamoeba histolytica Is a High-Fidelity DNA Ligase Involved in DNA Damage Repair

The protozoan parasite Entamoeba histolytica is exposed to reactive oxygen and nitric oxide species that have the potential to damage its genome. E. histolytica harbors enzymes involved in DNA repair pathways like Base and Nucleotide Excision Repair. The majority of DNA repairs pathways converge in their final step in which a DNA ligase seals the DNA nicks. In contrast to other eukaryotes, the genome of E. histolytica encodes only one DNA ligase (EhDNAligI), suggesting that this ligase is involved in both DNA replication and DNA repair. Therefore, the aim of this work was to characterize EhDNAligI, its ligation fidelity and its ability to ligate opposite DNA mismatches and oxidative DNA lesions, and to study its expression changes and localization during and after recovery from UV and H₂O₂ treatment. We found that EhDNAligI is a high-fidelity DNA ligase on canonical substrates and is able to discriminate erroneous base-pairing opposite DNA lesions. EhDNAligI expression decreases after DNA damage induced by UV and H₂O₂ treatments, but it was upregulated during recovery time. Upon oxidative DNA damage, EhDNAligI relocates into the nucleus where it co-localizes with EhPCNA and the 8-oxoG adduct. The appearance and disappearance of 8-oxoG during and after both treatments suggest that DNA damaged was efficiently repaired because the mainly NER and BER components are expressed in this parasite and some of them were modulated after DNA insults. All these data disclose the relevance of EhDNAligI as a specialized and unique ligase in E. histolytica that may be involved in DNA repair of the 8-oxoG lesions.

Red fluorescent protein (DsRFP) optimization for Entamoeba histolytica expression

Entamoeba histolytica genetic organization and genome structure is complex and under intense research. The genome is fully sequenced, and several tools have been developed for the molecular study of this organism. Nevertheless, good protein tracking tags that are easy to measure and image, like the fluorescent proteins are lacking. In this report, we codon-optimized the red fluorescent protein from the coral Discosoma striata (DsRFP) for its use in E. histolytica and demonstrated functionality in vivo. We envision that this protein can be widely used for the development of transcriptional reporter systems and protein-tagging applications.

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 E. histolytica Genome Structure and Virulence

The outcome of an Entamoeba histolytica infection is variable and the contribution of genetic diversity within E. histolytica to human disease is not fully understood. The information provided by the whole genome sequence of the E. histolytica reference laboratory strain (HM-1:IMSS) and thirteen additional laboratory strains have been made publically available. In this review theories on the source of the unexpected level of structural diversity found in E. histolytica will be discussed.

Bulky Trichomonad Genomes: Encoding a Swiss Army Knife

The trichomonads are a remarkably successful lineage of ancient, predominantly parasitic protozoa. Recent molecular analyses have revealed extensive duplication of certain genetic loci in trichomonads. Consequently, their genomes are exceptionally large compared to other parasitic protozoa. Retention of these large gene expansions across different trichomonad families raises the question: do these duplications afford an advantage? Many duplicated genes are linked to the parasitic lifestyle and some are regulated differently to their paralogues, suggesting they have acquired new functions. It is proposed that these large genomes encode a Swiss army knife of sorts, packed with a multitude of tools for use in many different circumstances. This may have bestowed trichomonads with the extraordinary versatility that has undoubtedly contributed to their success.

Comparative analysis of genotypic diversity in Entamoeba nuttalli isolates from Tibetan macaques and rhesus macaques in China

We have recently demonstrated the potentially virulent species Entamoeba nuttalli as one of the highly prevalent parasites in rhesus macaques (Macaca mulatta) in Mount Long-hu and Gui-yang in China. Tibetan macaque (Macaca thibetana) is a unique species living in China. To evaluate the prevalence of Entamoeba species in wild Tibetan macaques, we obtained 89 stool samples in Mount E-mei of Si-chuan Province in China. PCR analysis detected E. nuttalli, Entamoeba coli, and Entamoeba polecki ST2 in 17%, 42%, and 66% of the samples, respectively, whereas Entamoeba histolytica and Entamoeba dispar were undetected. This study is the first to report on the detection of E. nuttalli from Tibetan macaques. Six E. nuttalli isolates were obtained, 18S rRNA gene and six tRNA-linked short tandem repeat (STR) loci of the isolates were sequenced. The Mantel test results gave an r value of 0.97 of relationships between geographical distance and genetic diversity of Chinese E. nuttalli populations, indicating a significant isolation-by-distance effect in Chinese E. nuttalli according to the tRNA-STR loci sequences. Structural analysis of E. nuttalli isolates based on tRNA-linked STR loci demonstrated three Chinese E. nuttalli populations with their respective features, but the Gui-yang population was located in the middle. In the distance-based NJ tree, E. nuttalli isolates were divided into five different branches, and E-mei isolates were attributed to an independent branch to distinguish them from Gui-yang and Long-hu isolates. Genetic analysis in this study provided clues of the genetic differences between E. nuttalli isolates from Tibetan macaques and rhesus macaques in China.

Immune Evasion Mechanisms of Entamoeba histolytica: Progression to Disease

Entamoeba histolytica (Eh) is a protozoan parasite that infects 10% of the world's population and results in 100,000 deaths/year from amebic dysentery and/or liver abscess. In most cases, this extracellular parasite colonizes the colon by high affinity binding to MUC2 mucin without disease symptoms, whereas in some cases, Eh triggers an aggressive inflammatory response upon invasion of the colonic mucosa. The specific host-parasite factors critical for disease pathogenesis are still not well characterized. From the parasite, the signature events that lead to disease progression are cysteine protease cleavage of the C-terminus of MUC2 that dissolves the mucus layer followed by Eh binding and cytotoxicity of the mucosal epithelium. The host mounts an ineffective excessive host pro-inflammatory response following contact with host cells that causes tissue damage and participates in disease pathogenesis as Eh escapes host immune clearance by mechanisms that are not completely understood. Ameba can modulate or destroy effector immune cells by inducing neutrophil apoptosis and suppressing respiratory burst or nitric oxide (NO) production from macrophages. Eh adherence to the host cells also induce multiple cytotoxic effects that can promote cell death through phagocytosis, apoptosis or by trogocytosis (ingestion of living cells) that might play critical roles in immune evasion. This review focuses on the immune evasion mechanisms that Eh uses to survive and induce disease manifestation in the host.

Proteomic profiling of the infective trophozoite stage of Acanthamoeba polyphaga

Acanthamoeba polyphaga is a free-living protozoan pathogen, whose infective trophozoite form is capable of causing a blinding keratitis and fatal granulomatous encephalitis in humans. The damage caused by A. polyphaga trophozoites in human corneal or brain infections is the result of several different pathogenic mechanisms that have not yet been elucidated at the molecular level. We performed a comprehensive analysis of the proteins expressed by A. polyphaga trophozoites, based on complementary 2-DE MS/MS and gel-free LC-MS/MS approaches. Overall, 202 non-redundant proteins were identified. An A. polyphaga proteomic map in the pH range 3-10 was produced, with protein identification for 184 of 370 resolved spots, corresponding to 142 proteins. Additionally, 94 proteins were identified by gel-free LC-MS/MS. Functional classification revealed several proteins with potential importance for pathogen survival and infection of mammalian hosts, including surface proteins and proteins related to defense mechanisms. Our study provided the first comprehensive proteomic survey of the trophozoite infective stage of an Acanthamoeba species, and established foundations for prospective, comparative and functional studies of proteins involved in mechanisms of survival, development, and pathogenicity in A. polyphaga and other pathogenic amoebae.

Regulation of virulence of Entamoeba histolytica

Entamoeba histolytica is the third-leading cause of parasitic mortality globally. E. histolytica infection generally does not cause symptoms, but the parasite has potent pathogenic potential. The origins, benefits, and triggers of amoebic virulence are complex. Amoebic pathogenesis entails depletion of the host mucosal barrier, adherence to the colonic lumen, cytotoxicity, and invasion of the colonic epithelium. Parasite damage results in colitis and, in some cases, disseminated disease. Both host and parasite genotypes influence the development of disease, as do the regulatory responses they govern at the host-pathogen interface. Host environmental factors determine parasite transmission and shape the colonic microenvironment E. histolytica infects. Here we highlight research that illuminates novel links between host, parasite, and environmental factors in the regulation of E. histolytica virulence.

Erythrophagocytosis in Entamoeba histolytica and Entamoeba dispar: a comparative study

Entamoeba histolytica is the causative agent of human intestinal and liver amebiasis. The extraordinary phagocytic activity of E. histolytica trophozoites has been accepted as one of the virulence mechanisms responsible for their invasive capacity. The recognition of the noninvasive Entamoeba dispar as a different species has raised the question as to whether the lack of pathogenic potential of this ameba correlates with a limited phagocytic capacity. We have therefore compared the process of erythrophagocytosis in both species by means of light and video microscopy, hemoglobin measurement, and the estimation of reactive oxygen species (ROS). In the present study, we confirmed that E. dispar has lower erythrophagocytic capacity. We also observed by video microscopy a new event of erythrocyte opsonization-like in both species, being more characteristic in E. histolytica. Moreover, E. dispar showed a lower capacity to produce ROS compared with the invasive species and also showed a large population of amoebae that did not engulf any erythrocyte over time. Our results demonstrate that E. histolytica has a higher phagocytic capacity than E. dispar, including a higher rate of production of ROS in the course of ingesting red blood cells.

Immunity to amoeba

Amoebic infections in fish are most likely underestimated and sometimes overlooked due to the challenges associated with their diagnosis. Amoebic diseases reported in fish affect either gills or internal organs or may be systemic. Host response ranges from hyperplastic response in gill infections to inflammation (including granuloma formation) in internal organs. This review focuses on the immune response of Atlantic salmon to Neoparamoeba perurans, the causative agent of Amoebic Gill Disease (AGD).

Blastocystis: getting to grips with our guileful guest

Blastocystis, a common single-celled intestinal parasite of humans and animals, continues to puzzle clinical microbiologists, gastroenterologists, and general practitioners who are still unsure of the clinical significance of the organism. Here we consider some less well-addressed areas of Blastocystis research, which, facilitated by recent technological advances, could potentially turn out to be significant pathways to knowledge. First and foremost we discuss new trends in Blastocystis research, including the 'omics' perspectives, and then highlight some aspects of Blastocystis research in the context of host coevolution, its potential as a biomarker of intestinal functionality, and its relationship to other components of the human intestinal microbiota.

Worldwide genealogy of Entamoeba histolytica: an overview to understand haplotype distribution and infection outcome

Although Entamoeba histolytica is one of the most prevalent intestinal parasites, how the different strains of this species are distributed all over the world and how different genotypes are associated with the infection outcome are yet to be fully understood. Recently, the use of a number of molecular markers has made the characterization of several genotypes in those regions with high incidence of amoebiasis possible. This work proposes the first genealogy of E. histolytica, with an haplotype network based on two tRNA gene-linked array of Short Tandem Repeats (STRs) reported until today, and 47 sequences from 39 new isolates of Mexican Amoebic Liver Abscesses (ALA) samples. One hundred and three sequences were obtained from D-A locus, their information about the geographic region of isolation as well as clinical diagnosis were also collected. One hundred and five sequences from N-K2 locus were also obtained as well as the region of isolation, but the information about clinical diagnosis was not available in all cases. The most abundant and widely distributed haplotype in the world is the one of E. histolytica HM1:IMSS strain. This was found in Mexico, Bangladesh, Japan, China and USA and is associated to symptomatic patients as well as asymptomatic cyst passers. Many other haplotypes were found only in a single country. Both genealogies suggest that there are no lineages within the networks that may be related to a particular geographic region or infection outcome. A concatenated analysis of the two molecular markers revealed 12 different combinations, which suggests the possibility of genetic recombination events. The present study is the first to propose a global genealogy of this species and suggests that there are still many genotypes to be discovered. The genotyping of new isolates will help to understand the great diversity and genetic structure of this parasite.

Dysfunctions at human intestinal barrier by water-borne protozoan parasites: lessons from cultured human fully differentiated colon cancer cell lines

Some water-borne protozoan parasites induce diseases through their membrane-associated functional structures and virulence factors that hijack the host cellular molecules and signalling pathways leading to structural and functional lesions in the intestinal barrier. In this Microreview we analyse the insights on the mechanisms of pathogenesis of Entamoeba intestinalis, Giardia and Cryptosporidium observed in the human colon carcinoma fully differentiated colon cancer cell lines, cell subpopulations and clones expressing the structural and functional characteristics of highly specialized fully differentiated epithelial cells lining the intestinal epithelium and mimicking structurally and functionally an intestinal barrier.

Experimental amoebic liver abscess in hamsters caused by trophozoites of a Brazilian strain of Entamoeba dispar

It has been claimed that amoebic molecules such as amoebapore, galactose/N-acetyl galactosamine inhibitable lectin, and cysteine proteases are responsible for host tissue destruction and are present in both pathogenic Entamoeba histolytica and non-pathogenic Entamoeba dispar. Some reports have provided evidence that after infection with E. dispar, pathological changes may occur in some humans. The aim of this study was to evaluate E. dispar pathogenicity by comparing it to the pathogenicity of E. histolytica through liver abscesses induced in hamsters. Syrian golden hamsters were challenged by intrahepatic inoculation with the 03C E. dispar strain or with two strains of E. histolytica (HM1:IMSS and EGG) to compare their virulence grades. As control groups, we used bacterial flora and Pavlova's modified medium. Lesions were verified at 1, 3 and 6 days after inoculation. Multiplex Polymerase Chain Reaction was performed to characterize each strain using EdP1/EdP2 and EhP1/EhP2 primers. The EGG and HM1:IMSS E. histolytica strains and 03C E. dispar were able to cause liver lesions. The EGG strain caused extensive hepatic abscesses, and trophozoites were found in the lesions throughout the three periods of study. The HM1:IMSS strain caused smaller abscesses when compared to EGG lesions; however, trophozoites were observed at 1 and 3 days after inoculation. The 03C E. dispar strain caused intermediate abscesses when compared to the others; trophozoites were observed in all periods analyzed. The EGG strain caused progressive evolution of the injury, which differed from the HM1:IMSS and 03C strains. These results strongly suggest that the 03C E. dispar strain is pathogenic in the experimental hamster model. Additional studies are necessary to identify potential factors that regulate the manifestation of virulence of this strain and others.

Feed-forward regulation of phagocytosis by Entamoeba histolytica

The parasitic protozoan Entamoeba histolytica is aptly named for its capacity to destroy host tissue. When E. histolytica trophozoites invade the lamina propria of a host colon, extracellular matrices are degraded while host cells are killed and phagocytosed. The ability of E. histolytica to phagocytose host cells correlates with virulence in vivo. In order to better understand the mechanism of phagocytosis, we used an E. histolytica Affymetrix microarray chip to measure the total gene expression of phagocytic and nonphagocytic subpopulations. Using paramagnetic beads coated with a known host ligand that stimulates phagocytosis, phagocytic and nonphagocytic amoebae from a single culture were purified. Microarray analysis of the subpopulations identified 121 genes with >2-fold higher expression in phagocytic than in nonphagocytic amoebae. Functional annotation identified genes encoding proteins involved in actin binding and cytoskeletal organization as highly enriched gene clusters. Post hoc analyses of selected genes showed that the gene expression profile identified in the microarray experiment did not exist prior to cell sorting but rather was stimulated through phagocytosis. Further, these expression profiles correlated with an increase in phagocytic ability, as E. histolytica cultures exposed to an initial stimulus of phagocytosis showed increased phagocytic ability upon a second stimulus. To our knowledge, this is the first description of such feed-forward regulation of gene expression and phagocytic ability in a phagocyte.

A Multilocus Sequence Typing System (MLST) reveals a high level of diversity and a genetic component to Entamoeba histolytica virulence

Background

The outcome of an Entamoeba histolytica infection is variable and can result in either asymptomatic carriage, immediate or latent disease (diarrhea/dysentery/amebic liver abscess). An E. histolytica multilocus genotyping system based on tRNA gene-linked arrays has shown that genetic differences exist among parasites isolated from patients with different symptoms however, the tRNA gene-linked arrays cannot be located in the current assembly of the E. histolytica Reference genome (strain HM-1:IMSS) and are highly variable.

Results

To probe the population structure of E. histolytica and identify genetic markers associated with clinical outcome we identified in E. histolytica positive samples selected single nucleotide polymorphisms (SNPs) by multiplexed massive parallel sequencing. Profile SNPs were selected which, compared to the reference strain HM-1:IMSS sequence, changed an encoded amino acid at the SNP position, and were present in independent E. histolytica isolates from different geographical origins. The samples used in this study contained DNA isolated from either xenic strains of E. histolytica trophozoites established in culture or E. histolytica positive clinical specimens (stool and amebic liver abscess aspirates). A record of the SNPs present at 16 loci out of the original 21 candidate targets was obtained for 63 of the initial 84 samples (63% of asymptomatically colonized stool samples, 80% of diarrheal stool, 73% of xenic cultures and 84% of amebic liver aspirates). The sequences in all the 63 samples both passed sequence quality control metrics and also had the required greater than 8X sequence coverage for all 16 SNPs in order to confidently identify variants.

Conclusions

Our work is in agreement with previous findings of extensive diversity among E. histolytica isolates from the same geographic origin. In phylogenetic trees, only four of the 63 samples were able to group in two sets of two with greater than 50% confidence. Two SNPs in the cylicin-2 gene (EHI_080100/XM_001914351) were associated with disease (asymptomatic/diarrhea p = 0.0162 or dysentery/amebic liver abscess p = 0.0003). This study demonstrated that there are genetic differences between virulent and avirulent E. histolytica strains and that this approach has the potential to define genetic changes that influence infection outcomes.