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PubMed1969

Virulence Of Entamoeba Histolytica According To The Strains In Korea: III. Amebicial Response Of Antiamoebic Agents On Several Strains Of Entamoeba Histolytica In Vitro.

The amebicidal activity of traditional anitiamoebic drug (emetine, carbasone, diodoquin, chloroquine, atabrine, chloramphenicol and tertracycline) and newly appeared chemicals(niridazole, metronidazole and No. 8603 substance) were assayed by in vitro experiment using five strains of human originated E, histolytica. The variety of amebicidal activity of drugs by the strains were discussed. 1)Ranges of amoebicidal activity of traditional antiamoebic drugs kept almost similar titers of previous reports at the concentration; 1:5,000 to 1:20,000 with emetine hydrochloride, 1:10.000 to 1:20,000 with carbarsone, 1:8,000 to 1:16,000 with diodoquin, 1:50,000 with chloroquine, 1:1,000 to 1: 4,000 with atabrine,1:1,000 to 1:2,000 with chloramphencol and 1:5,000 to 1:8,000 with tetracycline. The newly appeared chemicals showed higher amebicidal titres at the concentration; 1:500,000 to 1:5,000,000 with niridazole, 1:50,000 to 1:100,000 with metronidazol and 1:100,000 to 1:500,000 with No.8603 substance. 2)Emetine, chloramphenicol and No. 8603 substance showed amebicidal activities at lower concentration to intestine originated amebae (YS 14, YS 15 and NAMRU II strain) than to liver originated amebae (YS 24 and YS 25 strain), while carbarsone, chloroquine and metronidazole showed the activity at higher concentrations. Diodoquin showed lower amebicidal titres to trophozoite borne amebae (NAMRU II, YS 24 and YS 25 strain) than to cyst borne amebae(YS 14 and YS 15 strain), but niridazole showed converse results. The concentration of atabrine for amebicidal activity was not constant according to strains of the amoeba, but tetracycline showed almost settled titers.

Journal Article↗
PubMed2006

New insights into the phylogeny of Entamoeba species provided by analysis of four new small-subunit rRNA genes.

Sequences of small-subunit rRNA genes have been obtained for four new isolates of Entamoeba. Phylogenetic analyses give new insights into the evolution of these organisms. A novel Entamoeba from pigs in Vietnam that produces uninucleate cysts proved to be unrelated to other uninucleated cyst-producing species. Revival of the name Entamoeba suis for this organism is proposed. Instead of being related to Entamoeba polecki, it shares a recent common ancestor with the non-encysting Entamoeba gingivalis in a lineage that is basal to the tetranucleate cyst-producing clade. This suggests that species producing cysts with four nuclei are descended from an ancestor that produced cysts with a single nucleus. An Entamoeba from a horse was isolated in culture. No cysts were observed in the original stool sample but the sequence is placed unequivocally within the clade of tetranucleate cyst-producing species with no other sequences being specifically related. Revival of the name Entamoeba equi for this organism is proposed. The Entamoeba ecuadoriensis sequence was found to be the most closely related to Entamoeba histolytica and Entamoeba dispar, as predicted, despite the organism having been an environmental isolate originally assigned to Entamoeba moshkovskii. Finally, a partial E. polecki gene sequence from a pig proved to be virtually identical to that of Entamoeba struthionis from an ostrich, suggesting that the latter name is a synonym.

Animals↗
PubMed1999

Phylogeny of the genera Entamoeba and Endolimax as deduced from small-subunit ribosomal RNA sequences.

We sequenced small-subunit ribosomal RNA genes (16S-like rDNAs) of 10 species belonging to the genera Entamoeba and Endolimax. This study was undertaken to (1) resolve the relationships among the major lineages of Entamoeba previously identified by riboprinting; (2) examine the validity of grouping the genera Entamoeba and Endolimax in the same family, the Entamoebidae; and (3) examine how different models of nucleotide evolution influence the position of Entamoeba in eukaryotic phylogenetic reconstructions. The results obtained with distance, parsimony, and maximum-likelihood analyses support monophyly of the genus Entamoeba and are largely in accord with riboprinting results. Species of Entamoeba producing cysts with the same number of nuclei from monophyletic groups. The most basal Entamoeba species are those that produce cysts with eight nuclei, while the group producing four-nucleated cysts is most derived. Most phylogenetic reconstructions support monophyly of the Entamoebidae. In maximum-likelihood and parsimony analyses, Endolimax is a sister taxon to Entamoeba, while in some distance analyses, it represents a separate lineage. The secondary loss of mitochondria and other organelles from these genera is confirmed by their relatively late divergence in eukaryotic 16S-like rDNA phylogenies. Finally, we show that the positions of some (fast-evolving) eukaryotic lineages are uncertain in trees constructed with models that make corrections for among-site rate variation.

Animals↗
PubMed2003

Detection and identification of entamoeba species in stool samples by a reverse line hybridization assay.

Classically, detection of Entamoeba histolytica is performed by microscopic examination for characteristic cysts and/or trophozoites in fecal preparations. Differentiation of E. histolytica cysts and those of nonpathogenic amoebic species is made on the basis of the appearance and the size of the cysts. However, by classical means objective tools for confirmation and quality control do not exist. Therefore, a reverse line blot hybridization assay was developed to detect a variety of Entamoeba species and genetic variants known to infect humans. The assay was performed after amplification with general Entamoeba-specific primers. The assay could identify four genetic variants of Entamoeba polecki-like cysts as well as E. histolytica, Entamoeba dispar, Entamoeba hartmanni, Entamoeba moshkovskii and Entamoeba coli and even mixed infections in a range of controls and fecal samples. This technique can be used as an additional standard for diagnosis, epidemiology, and quality control for amoebic infections.

Animals↗
PubMed2005

NADPH oxidase-derived reactive oxygen species-mediated activation of ERK1/2 is required for apoptosis of human neutrophils induced by Entamoeba histolytica.

The extracellular tissue penetrating protozoan parasite Entamoeba histolytica has been known to induce host cell apoptosis. However, the intracellular signaling mechanism used by the parasite to trigger apoptosis is poorly understood. In this study, we investigated the roles of reactive oxygen species (ROS), and of MAPKs in the Entamoeba-induced apoptosis of human neutrophils. The neutrophils incubated with live trophozoites of E. histolytica revealed a marked increase of receptor shedding of CD16 as well as phosphatidylserine (PS) externalization on the cell surface. The Entamoeba-induced apoptosis was effectively blocked by pretreatment of cells with diphenyleneiodonium chloride (DPI), a flavoprotein inhibitor of NADPH oxidase. A large amount of intracellular ROS was detected after exposure to viable trophozoites, and the treatment with DPI strongly inhibited the Entamoeba-induced ROS generation. However, a mitochondrial inhibitor rotenone did not attenuate the Entamoeba-induced ROS generation and apoptosis. Although E. histolytica strongly induced activation of ERK1/2 and p38 MAPK in neutrophils, the activation of ERK1/2 was closely associated with ROS-mediated apoptosis. Pretreatment of neutrophils with MEK1 inhibitor PD98059, but not p38 MAPK inhibitor SB202190, prevented Entamoeba-induced apoptosis. Moreover, DPI almost completely inhibited Entamoeba-induced phosphorylation of ERK1/2, but not phosphorylation of p38 MAPK. These results strongly suggest that NADPH oxidase-derived ROS-mediated activation of ERK1/2 is required for the Entamoeba-induced neutrophil apoptosis.

Animals↗
PubMed1983

Isolation and characterization of actin from Entamoeba histolytica.

Actin has been identified and purified partially from trophozoites of Entamoeba histolytica HMI-IMSS by a procedure that minimizes proteolysis. In cellular extracts, Entamoeba actin would copolymerize with muscle actin, but would not bind to DNase I or form microfilaments. Fractionation of the extracts by DEAE-cellulose and Sephadex G-150 chromatography yielded a purified actin that would copolymerize with rabbit skeletal muscle actin or polymerize alone into long filaments at 24 degrees C upon addition of 100 mM KC1 and 2 mM MgCl2. These filaments are not cold-stable and will depolymerize at 4 degrees C in 1 or 2 h. Entamoeba actin filaments bind phallotoxin with the same affinity as muscle actin and decorate with rabbit skeletal muscle heavy meromyosin. Entamoeba actin filaments activate the Mg2+ ATPase of heavy meromyosin to the same Vmax as muscle actin, but the Kapp is 2.8 times higher. Entamoeba actin is a single species with a slightly higher molecular weight than muscle actin (45,000) and a more acidic pI (5.4). The purified actin does not bind to DNase I, produce inhibition of the enzymatic activity, or block the binding of muscle actin. Comparison of the peptides obtained by limit digest with protease V8 from Staphylococcus aureus shows sequences with common mobility between alpha-actin and Entamoeba actin, but additional peptides are present which may account for the different properties of the Entamoeba actin. Finally, in vitro translation of mRNA from trophozoites produces a single polypeptide equivalent to the molecule purified from Entamoeba extracts.

Actins↗
PubMed2005

Unexpected diversity and differential success of DNA transposons in four species of entamoeba protozoans.

We report the first comprehensive analysis of transposable element content in the compact genomes (approximately 20 Mb) of four species of Entamoeba unicellular protozoans for which draft sequences are now available. Entamoeba histolytica and Entamoeba dispar, two human parasites, have many retrotransposons, but few DNA transposons. In contrast, the reptile parasite Entamoeba invadens and the free-living Entamoeba moshkovskii contain few long interspersed elements but harbor diverse and recently amplified populations of DNA transposons. Representatives of three DNA transposase superfamilies (hobo/Activator/Tam3, Mutator, and piggyBac) were identified for the first time in a protozoan species in addition to a variety of members of a fourth superfamily (Tc1/mariner), previously reported only from ciliates and Trichomonas vaginalis among protozoans. The diversity of DNA transposons and their differential amplification among closely related species with similar compact genomes are discussed in the context of the biology of Entamoeba protozoans.

Amino Acid Sequence↗
PubMedDate not supplied

A role for a galactose lectin and its ligands during encystment of Entamoeba.

In the life cycle of Entamoeba parasites alternate between the colon-dwelling trophozoite and the infectious cyst forms. The physiologic stimuli that trigger differentiation of trophozoites into cysts remain undefined. On the surface of the human-infecting Entamoeba, parasites express a galactose/N-acetylgatactosamine (gal/galNAc)-binding lectin, which plays demonstrated roles in contact-dependent lysis of target cells and resistance to host complement. Using a reptilian parasite, Entamoeba invadens, to study cyst formation in vitro, we found that efficient encystation was dependent on the presence of gal-terminated ligands in the induction medium. Precise concentration ranges of several gal-terminated ligands, such as asialofetuin, gal-bovine serum albumin (gal-BSA), and mucin, functioned in encystation medium to stimulate differentiation. Greater than 10 mM levels of free gal inhibited the amoeba aggregation that precedes encystation and prevented formation of mature cysts. Inhibitory levels of gal also prevented the up-regulation of genes which normally occurs at 24 h of encystation. The surface of Entamoeba invadens was found to express a gal lectin which has a heterodimeric structure similar to that of Entamoeba histolytica. The 30 kDa light subunit (LGL) of the E. invadens lectin is similar in overall size and sequence to the LGL of E. histolytica. The heavy subunits, however, differ in size, have an identical spacing of cysteines in their extracellular domains, and have highly conserved C-terminal transmembrane and cytoplasmic domains. These results suggest a new role for the Entamoeba gal lectins in monitoring the concentrations of gal ligands in the colon and contributing to stimuli that induce encystment.

Animals↗
PubMed1978

Two species of Entamoeba from white-tailed deer, Odocoileus virginianus, from Georgia.

Large numbers of 2 species of Entamoeba, Entamoeba coli and Entamoeba bovis, were recovered from captive white-tailed deer from Georgia. The trophozoite of the first ameba was a large form with a well-defined vesicular nucleus bearing a prominent eccentric endosome, abundant peripheral chromatin, and numerous periendosomal granules. Cytoplasmic vacuoles containing bacteria and other substances were common. Mature cysts were octonucleate. Glycogen vacuoles and irregularly shaped chromatoids were frequently present. This ameba was identified as Entamoeba coli. The trophozoite of the second ameba was small, with a typical Entamoeba nucleus. Cysts were uninucleate, containing numerous chromatoids resembling bars, splinters of wood, and irregular masses. There was occasionally a glycogen vacuole. This ameba was identified as Entamoeba bovis.

Animals↗
PubMed1997

Cloning and expression of chitinases of Entamoebae.

Entamoeba histolytica (Eh) and Entamoeba dispar (Ed) are protozoan parasites that infect hundreds of millions of persons. In the colonic lumen, amebae form chitin-walled cysts, the infectious stage of the parasite. Entamoeba invadens (Ei), which infects reptiles and is a model for amebic encystation, produces chitin synthase and chitinase during encystation. Ei cysts formation is blocked by the chitinase-inhibitor allosamidin. Here molecular cloning techniques were used to identify homologous genes of Eh, Ed, and Ei that encode chitinases (EC 3.2.1.14). The Eh gene (Eh cht1) predicts a 507-amino acid (aa) enzyme, which has 93 and 74% positional identities with Ed and Ei chitinases, respectively. The Entamoeba chitinases have signal sequences, followed by acidic and hydrophilic sequences composed of multiple tandemly arranged 7-aa repeats (Eh and Ed) or repeats varying in length (Ei). The aa compositions of the chitinase repeats are similar to those of the repeats of the Eh and Ed Ser-rich proteins. The COOH-terminus of each chitinase has a catalytic domain, which resembles those of Brugia malayi (33% positional identity) and Manduca sexta (29%). Recombinant entamoeba chitinases are precipitated by chitin and show chitinase activity with chitooligosacharide substrates. Consistent with previous biochemical data, chitinase mRNAs are absent in Ei trophozoites and accumulate to maximal levels in Ei encysting for 48 h.

Amino Acid Sequence↗
PubMed1997

Ecto-nucleotide triphosphatase activity in pathogenic and non-pathogenic Entamoeba: protection from the cytotoxic effects of extracellular ATP.

The nucleotide triphosphatase (NTPase) activity of Entamoeba species and of Entamoeba histolytica strains, was compared. In all cases, with the exception of Entamoeba moshkovskii, the enzyme was activated by Ca2+ and not by Mg2+ and preferentially hydrolysed UTP with decreasing activity for ATP and GTP. The NTPase activity was associated with both the intracellular and the plasma membrane sulphonylbenzoyl-adenosine (FSBA) of trophozoites in which the ATP-site was facing externally, as shown by fluoroinhibition of NTPase activity and protection by the substrate added prior to FSBA. The highest surface activity was found in Entamoeba invadens and in the virulent E. histolytica HM1-A clone (HM1-IMSS passaged thrice through hamster liver). Significant lower activity was observed in non-pathogenic Entamoeba spp. The addition of ATP to cultures of pathogenic amoebae resulted in cell growth inhibition and lysis. This deleterious effect of adding ATP to the cultures was reversed by the addition of Ca2+. ATP hydrolysis by the amoeba may alter extracellular ATP-dependent processes in the host, which may be important for the survival of the amoeba in vivo.

Acid Anhydride Hydrolases↗