The pathogenesis of amoebiasis

Evaluation of periodontitis parameters and plaque examination by microscopy: a report on 20 patients

The protozoan parasite Entamoeba gingivalis has long been detected in diseased gingival pockets. The parasite is found in 81% of diseased sites using PCR and in up to 100% using microscopy, whereas it is mostly absent from healthy gingival sites. The purpose of this study on 20 periodontitis patients was to analyze the characteristic biofilm using phase-contrast microscopy and evaluate the results of a novel antiparasitic, anti-inflammatory therapeutical approach. The therapeutic strategy, termed "Periodontal Healing Protocol Bonner Dunoyé" (PHPBD), is implemented in monthly appointments for 8 months, and a control visit at one year. It involves a disinfection protocol, subgingival calculus removal, patient training and the microscopic analysis of periodontal biofilm sulci. The practitioner also records bleeding on probing (BOP) and pocket depth (PD) to quantify healing. In all cases, the initial biofilm composed mainly of parasites, neutrophils, spirochetes, and other motile bacteria was progressively replaced by a white blood cell-free biofilm, consisting of motionless coccoid bacteria, filaments, and epithelial cells, indicative of healthy periodontium. Results were stable from month 8 to month 12. At one year, both BOP and PD values were greatly reduced (96%-100% decrease) compared to initial levels. The average sulcus clinical pocket healing toward the 1-3 mm PD group teeth was close to 99% overall patients. In conclusion, implementation of PHPBD appears to result in complete healing of periodontitis within 12 months, as determined by BOP, PD, biofilm microscopic monitoring and elimination of motile bacteria, parasites, and inflammatory cells. Thus, periodontal dysbiosis can be microscopically guided toward predictable eubiosis. Further studies are needed to evaluate long-term benefits.

The presence of yeasts and bacteria in free-living amoebae isolated from COVID-19 patients: concern for secondary infections

This study aimed to investigate the presence of SARS-CoV-2, yeasts, and bacteria in isolated free-living amoeba (FLA) from COVID-19 patients. Nasopharyngeal swabs (n = 60) were obtained from COVID-19 patients. After cultivation, morphological characterization, and RNA/DNA extraction, the presence of selected microorganisms was investigated. From 60 COVID-19 samples, 18 (30%) were positive for FLA. Acanthamoeba sp. Naegleria australiensis, Tetramitus sp. and Vermamoeba vermiformis were characterized in 12 (80%), 1 (6.66%), 2 (13.33%), and 7 (38.88%) of samples, respectively. SARS-CoV-2 RNA was not detected in FLA. Candida albicans, C. tropicalis, and C. parapsilosis were detected in (11/18; 61.11%), (3/18; 16.67%), and (3/18; 16.67%) of samples, respectively. Geotrichum candidum was detected in 10/18 (55.55%) of samples. Streptococcus spp. and Staphylococcus spp. were identified in 16/18 (88.88%) and 3/18 (16.67%), respectively. The presence of yeasts and bacteria signifies the possible role of FLA in distribution of secondary infections in susceptible patients.

Hemoglobin uptake and utilization by human protozoan parasites: a review

The protozoan disease is a major global health concern. Amoebiasis, leishmaniasis, Chagas disease, and African sleeping sickness affect several million people worldwide, leading to millions of deaths annually and immense social and economic problems. Iron is an essential nutrient for nearly all microbes, including invading pathogens. The majority of iron in mammalian hosts is stored intracellularly in proteins, such as ferritin and hemoglobin (Hb). Hb, present in blood erythrocytes, is a very important source of iron and amino acids for pathogenic microorganisms ranging from bacteria to eukaryotic pathogens, such as worms, protozoa, yeast, and fungi. These organisms have developed adequate mechanisms to obtain Hb or its byproducts (heme and globin) from the host. One of the major virulence factors identified in parasites is parasite-derived proteases, essential for host tissue degradation, immune evasion, and nutrient acquisition. The production of Hb-degrading proteases is a Hb uptake mechanism that degrades globin in amino acids and facilitates heme release. This review aims to provide an overview of the Hb and heme-uptake mechanisms utilized by human pathogenic protozoa to survive inside the host.

Amebic liver abscess: Clinico-radiological findings and interventional management

In its classic form, amebic liver abscess (ALA) is a mild disease, which responds dramatically to antibiotics and rarely requires drainage. However, the two other forms of the disease, i.e., acute aggressive and chronic indolent usually require drainage. These forms of ALA are frequently reported in endemic areas. The acute aggressive disease is particularly associated with serious complications, such as ruptures, secondary infections, and biliary communications. Laboratory parameters are deranged, with signs of organ failure often present. This form of disease is also associated with a high mortality rate, and early drainage is often required to control the disease severity. In the chronic form, the disease is characterized by low-grade symptoms, mainly pain in the right upper quadrant. Ultrasound and computed tomography (CT) play an important role not only in the diagnosis but also in the assessment of disease severity and identification of the associated complications. Recently, it has been shown that CT imaging morphology can be classified into three patterns, which seem to correlate with the clinical subtypes. Each pattern depicts its own set of distinctive imaging features. In this review, we briefly outline the clinical and imaging features of the three distinct forms of ALA, and discuss the role of percutaneous drainage in the management of ALA.

Phytochemicals and Biological Activities of Barleria (Acanthaceae)

Plant species belonging to the family Acanthaceae are globally known to possess various medicinal properties and have cultural and economic importance in both traditional medicine and horticulture. They are important to both animals and humans and are used as food or for ornamental purposes worldwide. Barleria is the third largest genus in the family Acanthaceae. A few of the highly important and reported species of Barleria include B. prionitis, B. cristata, B. grandiflora, and B. lupulina. The flowers, leaves, stems, roots, and seed extracts of plants belonging to this genus are rich in bioactive compounds and have exhibited significant medicinal potential for the treatment of various ailments and infections. Evidence derived from several studies has demonstrated the antioxidant, antibacterial, antifungal, anti-inflammatory, anticancer, antidiabetic, antiulcer, hepatoprotective, analgesic, antiamoebic, antihelminthic, antiarthritic, antihypertensive, antiviral properties and toxicity of extracts, in addition inhibition of acetylcholinesterase activity and biosynthesis of nanoparticles, of the plant and seed extracts of species belonging to Barleria. Studies have reported that bioactive compounds such as flavonoids, quinones, iridoids, phenylethanoid glycosides, the immunostimulant protein “Sankaranin”, and antibiotics isolated from Barleria species are resposnsible for the above biological activities. Traditionally, the genus Barleria has significant medicinal potential; however, there is a scarcity of information on various species that are yet to be evaluated. This review provides a comprehensive report on existing literature, concerning the phytochemistry and biological activities of the genus Barleria.

Venous thrombosis and segmental hypoperfusion in amebic liver abscess: MDCT demonstration and its implications

PURPOSE

To report venous thrombosis and associated perfusion defect in amebic liver abscess (ALA) using MDCT.

METHOD

MDCT images of 62 patients with ALA were reviewed for venous thrombosis and associated perfusion abnormalities.

RESULT

The study found 43 (69%) patients with venous thrombosis: portal vein thrombosis (PVT) occurred in 39, hepatic vein thrombosis (HVT) in 37 and inferior vena cava (IVC) thrombosis in 4. Combined PVT and HVT occurred in 33 (77%) patients. The portal vein thrombi remained localized in subsegmental branches in 25 patients and extended to segmental branches in 14. The hepatic vein thrombi were confined to peripheral branches in 18 patients; they progressed to the main trunk in 19 and to the IVC in 4. A wedge-shaped hypoattenuating zone suggesting ischemia was identified in 33 (77%) patients in portal phase: 31 had combined PVT and HVT, 2 had HVT alone, but none had PVT alone. It occurred significantly more often with combined PVT and HVT than HVT alone (p = 0.05). Arterial phase enhancement occurred in 2 of 13 patients with multiphasic CT. All patients were symptomatic despite medical therapy and therefore required percutaneous drainage. About half of the patients were identified with ruptured abscesses. Segmental atrophy was observed in seven of nine patients who underwent follow-up CT.

CONCLUSION

Combined PVT and HVT commonly occur with ALA and often manifests as segmental hypoperfusion in portal venous phase, indicating ischemia. The detection of such events by CT may be indicative of severe disease that requires aggressive management involving percutaneous drainage.

Venous thrombosis and segmental hypoperfusion in amebic liver abscess: MDCT demonstration and its implications

PURPOSE

To report venous thrombosis and associated perfusion defect in amebic liver abscess (ALA) using MDCT.

METHOD

MDCT images of 62 patients with ALA were reviewed for venous thrombosis and associated perfusion abnormalities.

RESULT

The study found 43 (69%) patients with venous thrombosis: portal vein thrombosis (PVT) occurred in 39, hepatic vein thrombosis (HVT) in 37 and inferior vena cava (IVC) thrombosis in 4. Combined PVT and HVT occurred in 33 (77%) patients. The portal vein thrombi remained localized in subsegmental branches in 25 patients and extended to segmental branches in 14. The hepatic vein thrombi were confined to peripheral branches in 18 patients; they progressed to the main trunk in 19 and to the IVC in 4. A wedge-shaped hypoattenuating zone suggesting ischemia was identified in 33 (77%) patients in portal phase: 31 had combined PVT and HVT, 2 had HVT alone, but none had PVT alone. It occurred significantly more often with combined PVT and HVT than HVT alone (p = 0.05). Arterial phase enhancement occurred in 2 of 13 patients with multiphasic CT. All patients were symptomatic despite medical therapy and therefore required percutaneous drainage. About half of the patients were identified with ruptured abscesses. Segmental atrophy was observed in seven of nine patients who underwent follow-up CT.

CONCLUSION

Combined PVT and HVT commonly occur with ALA and often manifests as segmental hypoperfusion in portal venous phase, indicating ischemia. The detection of such events by CT may be indicative of severe disease that requires aggressive management involving percutaneous drainage.

Iron-modulated virulence factors of Entamoeba histolytica

Entamoeba histolytica is a human parasite that causes amoebiasis, a disease that affects the colon and liver and is prevalent worldwide. This protozoan requires a high concentration of iron to survive and reproduce. Iron modulates the expression of parasite virulence factors, including hemoglobinases, hemoglobin-binding proteins and cysteine proteases, as well as proteins related to the amoebic cytoskeleton. This review summarizes the virulence factors that are affected by iron, resulting in upregulation or downregulation of E. histolytica genes. This review also discusses the functionality of iron in the mechanisms of pathogenesis.

Proteases from Entamoeba spp. and Pathogenic Free-Living Amoebae as Virulence Factors

The standard reference for pathogenic and nonpathogenic amoebae is the human parasite Entamoeba histolytica; a direct correlation between virulence and protease expression has been demonstrated for this amoeba. Traditionally, proteases are considered virulence factors, including those that produce cytopathic effects in the host or that have been implicated in manipulating the immune response. Here, we expand the scope to other amoebae, including less-pathogenic Entamoeba species and highly pathogenic free-living amoebae. In this paper, proteases that affect mucin, extracellular matrix, immune system components, and diverse tissues and cells are included, based on studies in amoebic cultures and animal models. We also include proteases used by amoebae to degrade iron-containing proteins because iron scavenger capacity is currently considered a virulence factor for pathogens. In addition, proteases that have a role in adhesion and encystation, which are essential for establishing and transmitting infection, are discussed. The study of proteases and their specific inhibitors is relevant to the search for new therapeutic targets and to increase the power of drugs used to treat the diseases caused by these complex microorganisms.

Effect of bovine lactoferrin in a therapeutic hamster model of hepatic amoebiasis

Entamoeba histolytica is the causative agent of amoebiasis, a disease that produces dysentery as a result of the perforation of the large intestine. This parasite often invades other organs, primarily the liver, leading to an amoebic liver abscess (ALA), which can cause death. Metronidazole is the drug of choice for the treatment of ALA; however, it produces toxic side effects in patients. Lactoferrin (Lf) is a glycoprotein of the innate immune response that sequesters iron in the mucosae. Lf possesses immune-regulatory properties, such as antiinflammatory and antioxidant activities. Moreover, the microbicidal activity of apoLf, which lacks bound iron, has been shown. In this study, we evaluated the therapeutic effect of bovine Lf (bLf) against ALA in a model of hepatic amoebiasis in hamsters. Interestingly, hamsters treated intragastrically with Lf (2.5 mg/100 g mass) over a period of 8 days showed no clinical signs of disease and ALA was effectively decreased, with only 0.63% detectable lesion, compared with 63% in untreated animals. Furthermore, liver function and blood cells approached normal levels among those receiving bLf treatment. These results suggest that bLf may aid in the therapy of amoebiasis, likely without producing undesirable effects in patients.

Use and endocytosis of iron-containing proteins by Entamoeba histolytica trophozoites

Iron is essential for nearly all organisms; in mammals, it is part of proteins such as haemoglobin, and it is captured by transferrin and lactoferrin. Transferrin is present in serum, and lactoferrin is secreted by the mucosa and by neutrophils at infection sites, as a host iron-withholding response, sequestering iron away from invading microorganisms. Additionally, all cells contain ferritin, which sequesters iron when its intracellular levels are increased, detoxifying and preventing damage. Liver ferritin contains 50% of iron corporal reserves. During evolution, pathogens have evolved diverse strategies to obtain iron from their hosts in order to survive. The protozoan Entamoeba histolytica invades the intestinal mucosa, causing dysentery, and the trophozoites often travel to the liver producing hepatic abscesses; thus, intestine and liver proteins could be important iron supplies for E. histolytica. We found that E. histolytica trophozoites can grow in both ferrous and ferric iron, and that they can use haemoglobin, holo-transferrin, holo-lactoferrin, and ferritin as in vitro iron sources. These proteins supported the amoeba growth throughout consecutive passages, similarly to ferric citrate. By confocal microscopy and immunoblotting, iron-binding proteins were observed specifically bound to the amoeba surface, and they were endocytosed, trafficked through the endosomal/lysosomal route, and degraded by neutral and acidic cysteine-proteases. Transferrin and ferritin were mainly internalized through clathrin-coated vesicles, and holo-lactoferrin was mainly internalized by caveola-like structures. In contrast, apo-lactoferrin bound to membrane lipids and cholesterol, inducing cell death. The results suggest that in vivo trophozoites secrete products that can destroy enterocytes, erythrocytes, and hepatocytes, releasing transferrin, haemoglobin, ferritin, and other iron-containing proteins, which, together with lactoferrin derived from neutrophils and acinar cells, could be used as abundant iron supplies by amoebas.

Effect of iron on adherence and cytotoxicity of Entamoeba histolytica to CHO cell monolayers

Iron is an essential element for almost all living organisms. The possible role of iron for growth, adherence and cytotoxicity of Entamoeba histolytica was evaluated in this study. The absence of iron from TYI-S-33 medium stopped amebic growth in vitro. However, iron concentrations in the culture media of 21.4-285.6 microM did not affect the growth of the amebae. Although growth was not retarded at these concentrations, the adhesive abilities of E. histolytica and their cytotoxicities to CHO cell monolayer were correlated with iron concentration. Amebic adhesion to CHO cell monolayers was significantly reduced by low-iron (24.6 +/- 2.1%) compared with 62.7 +/- 2.8 and 63.1 +/- 1.4% of amebae grown in a normal-iron and high-iron media, respectively. E. histolytica cultured in the normal- and high-iron media destroyed 69.1 +/- 4.3% and 72.6 +/- 5.7% of cultured CHO cell monolayers, but amebae grown in the low-iron medium showed a significantly reduced level of cytotoxicity to CHO cells (2.8 +/- 0.2%). Addition of divalent cations other than iron to amebic trophozoites grown in the low-iron medium failed to restore levels of the cytotoxicity. However, when E. histolytica grown in low-iron medium were transferred to normal-iron medium, the amebae showed completely restored cytotoxicity within 7 days. The result suggests that iron is an important factor in the adherence and cytotoxicity of E. histolytica to CHO cell monolayer.

Immunohistochemical characterization of human fulminant amoebic colitis

In cases of fulminant amoebic colitis we have determined the interactions between Entamoeba histolytica trophozoites and immune cells in order to better understand the pathophysiology of amoebic colitis. Eleven specimens of amoebic colitis and five specimens of colon without amoebic lesions were studied. Trophozoites and immune cells were located by topographic stains, histochemistry and immunohistochemistry. Trophozoites were seen in both damaged and undamaged areas of the colonic mucosa. Specimens of fulminant amoebic colitis showed: (a) an increase in IgA+, IgG+ B cells and neutrophils; (b) a reduction in IgM+ B cells, CD8+ T cells, macrophages, eosinophils and mast cells; and (c) no change in the number of NK and CD4+ T cells. The cellular infiltrate in amoebic colitis may represent the combined effects of amoebic monocyte locomotion inhibitory factor and switching of IgM+ B cells to IgG+ and IgA+ plasma cells, induced by amoebic antigens. Tissue damage in the absence of trophozoites may result from ischaemia or host immune responses.

Microbicidal action of lactoferrin and lactoferricin and their synergistic effect with metronidazole in Entamoeba histolytica

Lactoferrin (Lf), in its iron-free form, has been shown to inhibit the growth of pathogenic microorganisms. In the light of new agents to control amoebiasis, the microbicidal activity of human and bovine Lf and bovine lactoferricin (bLfcin, fragment 4-14), and of each combined with metronidazole, the main drug used in amoebiasis, was evaluated in trophozoites of Entamoeba histolytica. Both lactoferrins and bLfcin were able to kill amoebas in a concentration-dependent manner. This killing effect was modulated according to the culture age, pH, and temperature. Parasites obtained from the stationary phase were more susceptible to Lf than those from the early exponential phase. The effect of Lf and its derived peptide, bLfcin, was prevented by both Fe2+ and Fe3+. However, the divalent cations Mg2+ and Ca2+ prevented the killing effect of Lf but not of bLfcin. A synergistic amoebicidal effect was found between metronidazole and human Lf, bovine Lf, or bLfcin. These data suggest that Lf and bLfcin might be used in amoebiasis if they are administered with a low dose of metronidazole to diminish the toxicity of this drug. Thus, Lf and bLfcin are therapeutically potential candidates for use as antiamoebics in patients.

Sexual dimorphism in the control of amebic liver abscess in a mouse model of disease

Amebic liver abscess (ALA) is the most common extraintestinal manifestation of human infection by the enteric protozoan parasite Entamoeba histolytica. In contrast to intestinal infection, ALA greatly predominates in males but is rare in females. Since humans are the only relevant host for E. histolytica, experimental studies concerning this sexual dimorphism have been hampered by the lack of a suitable animal model. By serial liver passage of cultured E. histolytica trophozoites in gerbils and mice, we generated amebae which reproducibly induce ALA in C57BL/6 mice. Interestingly, all animals developed ALA, but the time courses of abscess formation differed significantly between the genders. Female mice were able to clear the infection within 3 days, whereas in male mice the parasite could be recovered for at least 14 days. Accordingly, male mice showed a prolonged time of recovery from ALA. Immunohistology of abscesses revealed that polymorphonuclear leukocytes and macrophages were the dominant infiltrates, but in addition, gamma,delta-T cells, NK cells, and natural killer T (NKT) cells were also present at early times during abscess development, whereas conventional alpha,beta-T cells appeared later, when female mice had already cleared the parasite. Interestingly, male and female mice differed in early cytokine production in response to ameba infection. Enzyme-linked immunospot assays performed with spleen cells of infected animals revealed significantly higher numbers of interleukin-4-producing cells in male mice but significantly higher numbers of gamma interferon (IFN-gamma)-producing cells in female mice. Early IFN-gamma production and the presence of functional NKT cells were found to be important for the control of hepatic amebiasis as application of an IFN-gamma-neutralizing monoclonal antibody or the use of NKT knockout mice (Valpha14iNKT, Jalpha 18(-/-)) dramatically increased the size of ALA in female mice. In addition, E. histolytica trophozoites could be reisolated from liver abscesses of Jalpha18(-/-) mice on day 7 postinfection, when wild-type mice had already cleared the parasite. These data suggest that the sexual dimorphism in the control of ALA is due to gender-specific differences in early cytokine production mediated at least in part by NKT cells in response to E. histolytica infection of the liver.

Human amoebic hepatic abscess: in situ interactions between trophozoites, macrophages, neutrophils and T cells

Amoebic liver abscesses (ALA) are the most frequent and severe extraintestinal clinical presentations of amoebiasis. During the early establishment of amoebae in the liver parenchyma, as well as during the extension of the tissue necrosis, parasites interact with the parenchymal liver cells and, as a consequence of these interactions, hepatocytes can be destroyed and host immune cells can become activated. However, little is known about the nature of these interactions in the liver or about the factors involved in the local immune response. In this investigation we studied the localization of Entamoeba histolytica trophozoites, TCD4+, TCD8+ cells, CD68+ macrophages and CD15+ neutrophils in human ALA using immunohistochemical techniques. Trophozoites were found close to undamaged hepatocytes in both lysed and non-lysed areas with either sparse or abundant inflammatory infiltrate. CD8+ cells were more abundant than CD4+ T cells. CD 68+ macrophages and CD15+ neutrophils were also detected, suggesting that neutrophils, macrophages and T cells might be related to the local host immune mechanisms in ALA. We also found that E. histolytica possesses proteins recognized by antibodies raised against inducible nitric oxide synthase.

Entamoeba histolytica: acute granulomatous intestinal lesions in normal and neutrophil-depleted mice

To study the role of neutrophils in the innate resistance to Entamoeba histolytica intestinal infection in mice, animals were treated with anti-neutrophil monoclonal antibodies prior to intracecal parasite inoculation and the resulting lesions were compared with normal mice that had been equally infected. In contrast to our previous finding that neutrophils are critical in eliminating E. histolytica infection in the liver, we show here that neutrophils are not absolutely required to eliminate E. histolytica infection from the intestine. Although the neutrophils are not critical for resolution of the E. histolytica infection, neutrophils do appear to provide some measure of protection as the intestinal amoeba burden was higher at early timepoints after infection in the neutropenic animals. In addition, we found that while both the normal and the neutrophil-depleted mice developed ulcerative lesions in the colon, the neutropenic mice had an increased frequency of granulomas that formed around the amoeba. Thus, our findings appear to be the first evidence showing that granulomatous inflammation can occur after intestinal infection in mice using axenically cultured amoeba.

Early interactions of Entamoeba histolytica trophozoites with parenchymal and inflammatory cells in the hamster liver: an immunocytochemical study

We studied the early in situ interactions of live and fixed Entamoeba histolytica trophozoites with hamster hepatic parenchymal and inflammatory cells using immunoperoxidase and immunoelectronmicroscopy. Close contact between trophozoites and endothelial cells and the diffusion of amoebic molecules from trophozoites towards nearby endothelial cells and distant hepatocytes were observed. The inflammatory cells around the amoebae and the remnants of parenchymal cells and hepatocytes located close to the lesion had a positive stain for amoebic molecules. In the amoebae, at the ultrastructural level, molecules were attached to the membranes and inside the vesicles. These molecules were apparently released into the space formed between the parasite and the endothelial cells. The endothelial cells and the nearby and distant hepatocytes captured amoebic molecules, and later they became necrotic. Contrarily, when fixed amoebae were inoculated, amoebic molecules were captured by endothelial cells and polymorphonuclear (PMN) leukocytes, but neither suffered any damage. In this work, we are presenting evidence clearly showing that some molecules of the amoeba can diffuse away long distances causing cytotoxic effects and even necrosis on hepatic cells of hamster liver without the need of the trophozoite being in close contact with the target cells. They also may promote lytic or proinflammatory effects by inducing the secretion of enzymes or cytokines in other nonparenchymal cells, like PMN leukocytes and endothelial cells. Our results suggest that the accepted mechanisms of cytotoxicity by amoebae are not exclusively restricted to the following sequence: adhesion, phagocytosis, and necrosis.

RAPD in the analysis of isolates of Entamoeba histolytica

Genetic variability in Entamoeba histolytica was analyzed by random amplified polymorphic DNA (RAPD) using ten arbitrary primers. Due to intrinsic characteristics of the RAPD technique only axenic samples were analyzed. since the presence of any microorganism in the cultures interfered in the DNA profile by generating RAPDs not pertaining to E. histolytica. The RAPD profiles of E. histolytica samples isolated from patients with different clinical manifestations from different regions of the Americas shared about 70% of the bands produced. These profiles were compared to those obtained for E. moshkorskii, and E. invadens. The combined data for the ten primers were used in the phenetic analysis of all the isolates studied by using the Dice similarity coefficient as the genetic distance measure between the samples. Three distinct groups could be separated by phenon line: one including E. moshkovskii samples, which shared > 90% of the RAPDs produced by the different primers; one consisting solely of E. invadens; and a third comprising samples of E. histolytica, which showed considerable intraspecific variability.

Giardia duodenalis: inter-strain variability of proteins, antigens, proteases, isoenzymes and nucleic acids

Giardia duodenalis isolates from asymptomatic or symptomatic patients and from animals present similarities and differences in the protein composition, antigenic profile, pattern of proteases and isoenzymes, as well as in nucleic acids analysis. In the present overview, these differences and similarities are reviewed with emphasis in the host-parasite interplay and possible mechanisms of virulence of the protozoon.

Interaction of laminin with Entamoeba histolytica cysteine proteinases and its effect on amebic pathogenesis

The Entamoeba histolytica 27-kDa cysteine proteinases exhibit striking binding specificities for immobilized laminin over other components of the extracellular matrix, such as collagen and fibronectin. Inactivation of the proteinase with the active-site inhibitor L-trans-epoxysuccinyl-leucylamido(4-guanidino)butane abolishes laminin binding by the enzyme, and conversely, laminin inhibits cleavage of a fluorogenic dipeptide substrate of the amebic cysteine proteinase, suggesting that the substrate binding pocket of the enzyme is involved in the binding of laminin. The addition of laminin but not fibronectin or collagen to E. histolytica trophozoites significantly reduces amebic liver abscess formation in severe combined immunodeficient mice, further supporting the hypothesis that E. histolytica cysteine proteinases play an important role in amebic pathogenesis. The specific interaction of amebic proteinases with laminin may be exploited in designing new inhibitors of these enzymes.

Induction of the iron-containing superoxide dismutase in Entamoeba histolytica by a superoxide anion-generating system or by iron chelation

The regulation of superoxide dismutase (SOD) expression was studied in 4 Entamoeba histolytica isolates. In comparison to anaerobic conditions, cultivation of the amoebae in the presence of superoxide radical anions or a ferrous iron chelator revealed substantial increase of SOD expression. Under the different culture conditions, all SOD activity could be exclusively attributed to an iron-containing type (FeSOD). Northern blot analysis revealed that FeSOD expression was regulated on the transcriptional level. Within the 5'-flanking region of the amoebic FeSOD gene, a 19-bp fragment was found with 68% sequence identity to the consensus motif of the binding site for the ferric uptake regulation gene product of Escherichia coli. Electrophoretic mobility shift assays with this 19-bp fragment and with amoebic nuclear extracts revealed specific DNA/protein complex formation. The results indicate that the regulation of E. histolytica FeSOD expression is similar to that of the manganese-containing SOD (MnSOD) of E. coli.

Coding of hemolysins within the ribosomal RNA repeat on a plasmid in Entamoeba histolytica

The pathogenesis of amoebic dysentery is a result of cytolysis of the colonic mucosa by the parasitic protozoan Entamoeba histolytica. The cytolysis results in extensive local ulceration and allows the amoeba to penetrate and metastasize to distant sites. Factors involved in this process were defined with three clones that express hemolytic activities in Escherichia coli. These potential amoebic virulence determinants were also toxic to human colonic epithelial cells, the primary cellular targets in amoebal invasion of the large intestine. The coding sequences for the hemolysins were close to each other on a 2.6-kilobase segment of a 25-kilobase extrachromosomal DNA element. The structural genes for the hemolysins were within inverted repeats that encode ribosomal RNAs.

A fluorescence-based quantitative adhesion assay to study interactions between Entamoeba histolytica and human enterocytes. Effect of proinflammatory cytokines

In order to study the initial events during infection of target cells by the enteric pathogen Entamoeba histolytica, we developed a quantitative adhesion assay based on the use of a human colonic cell line (CaCo-2) and biotinylated amoebae tagged with fluorescein. To prevent the strong and rapid lytic activity of Entamoeba histolytica on colonic cells, which would otherwise impede the study of the primary adhesion steps, parasites were mildly fixed, biotinylated and labelled with streptavidin-FITC. After labelled parasites have bound to enterocytes, nonadhered amoebae are removed by washing and attached parasites quantified by means of an automated fluorescence plate reader. The bioassay is simple, nonhazardous and can be completed in 1.5 h. We were able to detect ranges from 200 to 20,000 fluorescent parasites per microwell in a 96-well plate, containing approximately 10(5) colonic cells. Fluorescence intensity (arbitrary units) increased in direct relationship to the number of parasites added per well, and was not limited by the size of the culture plate (96, 24 or six wells). As an example of the value of this assay, two proinflammatory cytokines (interleukin-1, (IL-1 beta) and interferon-gamma (IFN-gamma) known to influence the adhesion properties of endothelial and epithelial cells, were used to assess their effects upon enterocyte-entamoeba binding. The increase in amoebae binding revealed by cytokine treatment to enterocytes suggests that the parasite may take advantage of inflammatory stimuli in order to increase its binding to colonic epithelium. We believe this rapid, sensitive and simple method offers the potential for large scale screening assays to study the immunobiology of this protozoal infection by analysing the mechanisms involved in the primary interactions between Entamoeba histolytica and enterocytes.

Entamoeba histolytica: correlation of the cytopathic effect of virulent trophozoites with secretion of a cysteine proteinase

Work from several laboratories suggests a correlation between expression of cysteine proteinase activity and the cytopathic effect of virulent HM1 strain Entamoeba histolytica trophozoites on cultured cell monolayers. Consistent with this relationship, we find that L-6 trophozoites, mutants cloned from the HM1 parent strain, are deficient in both proteinase expression and cytopathic effect. Three other clones, with proteinase expression equal to or greater than that of the HM1 strain, express the cytopathic effect. Furthermore, a nontoxic specific proteinase inhibitor, Z-phenylalanyl-alanyl-CH2F, inhibits the cytopathic effect of live trophozoites in a dose-dependent manner. These results support the hypothesis that expression and release of the cysteine proteinase is an important factor in producing the cytopathic effect, presumably by its degradation of cell anchoring proteins.

Non-pathogenic Entamoeba histolytica: functional and biochemical characterization of a monoxenic strain

We have cultured under monoxenic conditions and characterized an Entamoeba histolytica clone, MAV-I CINVESTAV (MAV-I), obtained from feces from an asymptomatic carrier. The clone shows the non-pathogenic E. histolytica zymodeme type I, which did not change through the process of monoxenization. Clone MAV-I was non-pathogenic in both in vivo and in vitro tests, and it did not have a functional 112-kDa adhesin. As far as we know, this is the first non-pathogenic monoxenic strain reported. Clone A (strain HM1:IMSS), a highly virulent clone with pathogenic zymodeme type II, and which has the 112-kDa adhesin, was used as a control. Protein patterns from both clones were almost identical in one-dimensional gels. In two-dimensional gels, differences in high-molecular-weight proteins were detected. Clone MAV-I adhered and phagocytosed only 12% of the red blood cells adhered and phagocytosed by clone A. MAV-I trophozoites did not destroy cell culture monolayers and did not produce hepatic abscesses in hamsters. They also showed deficiency in protease activity. The absence of virulence in clone MAV-I correlated directly with the absence of a functional 112-kDa adhesion, supporting the role that this protein plays in virulence.

Giardia lamblia: isoenzyme analysis of 19 axenic strains isolated from symptomatic and asymptomatic patients in Mexico

Infection of the small intestine of humans with the parasitic protozoon Giardia lamblia may have an asymptomatic course, or it may produce acute or chronic diarrhoea. In order to establish if the different clinical outcome of giardiasis in children could be due, at least partially, to strain differences, 19 isolates from asymptomatic and symptomatic cases studied in Mexico City were cultured under axenic conditions and the isoenzyme electrophoretic patterns of 10 different enzymes were compared. Strains from carriers and from symptomatic cases of giardiasis were equally amenable to isolation and axenization. Isoenzyme electrophoresis demonstrated remarkable homogeneity in 7 enzyme patterns for all 19 isolates, except for phosphoglucomutase, for which 3 different zymodemes were found. Therefore, these isolates of G. lamblia, obtained from a single geographical location, tended to be genetically homogeneous. In addition, there were no consistent zymodeme differences between isolates from symptomatic and asymptomatic human infections.