Gut microbiome communication with bone marrow regulates susceptibility to amebiasis

The microbiome provides resistance to infection. However, the underlying mechanisms are poorly understood. We demonstrate that colonization with the intestinal bacterium Clostridium scindens protects from Entamoeba histolytica colitis via innate immunity. Introduction of C. scindens into the gut microbiota epigenetically altered and expanded bone marrow granulocyte-monocyte progenitors (GMPs) and resulted in increased intestinal neutrophils with subsequent challenge with E. histolytica. Introduction of C. scindens alone was sufficient to expand GMPs in gnotobiotic mice. Adoptive transfer of bone marrow from C. scindens-colonized mice into naive mice protected against amebic colitis and increased intestinal neutrophils. Children without E. histolytica diarrhea also had a higher abundance of Lachnoclostridia. Lachnoclostridia C. scindens can metabolize the bile salt cholate, so we measured deoxycholate and discovered that it was increased in the sera of C. scindens-colonized specific pathogen-free and gnotobiotic mice, as well as in children protected from amebiasis. Administration of deoxycholate alone increased GMPs and provided protection from amebiasis. We elucidated a mechanism by which C. scindens and the microbially metabolized bile salt deoxycholic acid alter hematopoietic precursors and provide innate protection from later infection with E. histolytica.

Learning from the research on amebiasis and gut microbiome: Is stimulation by gut flora essential for effective neutrophil mediated protection from external pathogens?

Amebiasis, caused by intestinal infection with Entamoeba histolytica, is one of the leading causes of parasite infection-related mortality and morbidity globally. Although its pathogenesis, including determinant factors of infection outcome, remains unclear, recent clinical data indicate that the gut microbiome plays a role in determining the severity of amebiasis. Recently, we investigated the effects of the gut microbiome on neutrophil mediated protection from E. histolytica infection using a mouse model. We identified that surface expression of CXCR2 on neutrophils was diminished in mice with dysbiosis, which resulted in decreased neutrophil recruitment to the infection site, allowing more aggressive intestinal tissue damage by E. histolytica. Our results indicated that oxidase activity during E. histolytica infection was also diminished after dysbiosis, consistent with the results from prior research. Thus, the gut microbiome plays an important role in regulating neutrophil phenotype when fighting against external pathogens.

Role of cysteine proteinase of Entamoeba histolytica in target cell death

The bacterial flora of the intestine plays an important role in the virulence caused by Entamoeba histolytica. Cysteine proteinase (CP), an amoebic virulence factor, plays a major role in host cell destruction. The mechanism of increased virulence following bacterial co-association is not understood. We studied CP of E. histolytica HM1:IMSS which was co-associated with Escherichia coli K12 strain pre-incubated with GalNAc or CP specific inhibitor E 64. Co-association of E. histolytica with bacteria enhanced CP activity 3-6-fold as assessed by azocasein assay and substrate gel electrophoresis showed bands at molecular weights of 28, 35 and 56 kDa. Northern and Western blot analysis showed increase in ehcp2 and ehcp5 gene expression. Trophozoites co-associated with E. coli showed greater cytotoxicity of BHK cells by a 51Cr release assay than trophozoites that had not been co-associated; this enhancement was abolished by E-64 treatment. The killing of BHK 21 targets by E. histolytica was characterized by DNA laddering which was not inhibited with E-64. GalNAc pre-incubation of trophozoites reduced cytotoxicity and DNA laddering, while E. coli co-associated E. histolytica showed smearing with faint laddering of BHK implicating both necrosis and apoptosis. Hence, bacterial co-association increases CP activity and CP gene expression and contributes to the necrosis of the target cell.

Biological aspects of a Brazilian strain of Entamoeba dispar

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

[Infectious etiology of dysenteric syndromes at the Principal Hospital of Dakar in 1999 and 2000]

Dysenteric syndromes are relatively frequent in tropical areas, due essentially to infectious etiologies, constituted by flimsy pathogenic agents outside and possibilities of laboratory investigations little available. The authors evaluated during two years (1990-2000) the results of 399 parasitological examinations and 419 bacteriological examinations concerning dysenteric syndromes admitted to the laboratory of "Hopital Principal de Dakar". The objective of these examination is to contribute to the management of cases. The patients are divided into two groups: the first group is constituted by children less than two years old hospitalised in the pediatric services, and the second group includes all the other patients. The parasitological studies schow that parasitic etiologies are almost non existent in the first group while in the second group, they are essentially represented by Entamoeba histolytic with 19.5% of prevalence. The bacteriological studies show 42.7% of positivity rate in the first group and 19.5% in the second group with a predominance of E. coli and Shigella dysenteriae. The prevalence or pathogenic agents associations is not neglectable: they represent 8% or positive results with a predominance of amoeba-Shigella association. These results confirm the necessity of a best case management during the preanalytic phase in order to improve the scores of positivity and the particularities of hospitalised children les than two years old, to when the frequency of observed cases is high with bacteriological etiologies essentially (E. coli EPEC+, Nosocomial bacteria).

Bacterium-assisted invasion of Entamoeba histolytica through human enteric epithelia in two-compartment chambers

Entamoeba histolytica trophozoites initiate amebiasis by invasion into the enteric mucosa. It is the aim of our experiments to understand how bacteria and leukocytes act during amebic invasion through enteric cell layers. Cocultures were established in two-compartment chambers and studied by measurement of transepithelial electrical resistance (TER) and by histological examination. Trophozoites caused a decrease in TER that was followed by formation of holes in the enteric cell layer and transfilter migration of trophozoites. Phagocytosed bacteria activated trophozoites that opened the intracellular junctions and provided access for the invasion of bacteria. Leukocytes had no effect on the different steps of invasion of the trophozoites through the human enteric cell layers. We conclude that trophozoites, eventually assisted by enteric bacteria, disrupt enterocytic tight junctions before they open the enteric cell layer and invade through it.

Inhibitory activity of saccharomyces yeasts on the adhesion of Entamoeba histolytica trophozoites to human erythrocytes in vitro

Adhesion to target cells represents the first step in infection by Entamoeba histolytica. Binding of axenic amoeba (HMI strain) to human red cells in vitro was employed as a model of the adhesion process. The influence of precontact of trophozoites with suspensions of live Saccharomyces boulardii yeasts, their fractions (membranes and yeast-content supernatant before and after filtration to eliminate the membrane) or yeast culture medium before and after fermentation was investigated. N-Acetylgalactosamine (GalNAC) was employed as the reference inhibitory sugar. The percentage of amoebae bearing red cells after pretreatment of amoebae with the various suspensions and derivates was determined. Adhesion was also evaluated by scanning electron microscopy (SEM). Pretreatment of amoebae with the live yeast suspension led to a significant reduction in the percentage of adhesion [32% vs 70% in the phosphate-buffered saline (PBS) control]. Reduced adhesion was also observed with the filtered and unfiltered supernatant of the yeast suspension homogenate [32% and 34%, respectively, vs 69% in the PBS control], yeast culture medium at the end of fermentation [49% vs 76% in the PBS control] and GalNAC [32% vs 72% in the PBS control]. SEM showed a decrease in the number of amoebae bearing red cells and a reduction in the number of red cells adhering to amoebae. We conclude that substances produced by the yeasts compete with red cells for adhesion sites on amoebae.

[Fatal transmural colitis caused by Entamoeba histolytica. Differential diagnosis of chronic inflammatory bowel disease and colon cancer]

Perforation of the colon is a rare but frequently fatal complication of amoebiasis. We report a case of a 53 year-old male, with no history of travel abroad, who was admitted to hospital with haematochezia. A tumor of the rectum was diagnosed clinically. Due to acute intestinal obstruction, laparotomy was performed, revealing multiple perforations of the large bowel and severe peritonitis leading to subtotal colectomy. The histological examinations revealed transmural amoebic colitis. The patient died due to multi-organ failure.

Ameba-bacterium relationship in amebiasis

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Amebic dysentery. Animal model: experimental Entamoeba histolytica infection in the germfree guinea pig

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The surgical management of amoebiasis in children

Five children with severe complications of acute amoebic dysentery are described. The results of a simple defunctioning proximal ileostomy are encouraging. Prior administration of anti-amoebic therapy and postoperative intensive medical care are mandatory for a successful outcome.

Treatment of children with acute amoebic dysentery. Comparative trial of metronidazole against a combination of dehydroemetine, tetracycline, and diloxanide furoate

Metronidazole cured 17 out of 20 children with acute amoebic dysentery. The 3 failures were later treated with dehydroemetine, tetracycline, and diloxanide furoate, but 2 required further courses of amoebicides before they were cured. A combination of dehydroemetine, tetracycline, and diloxanide furoate produced cure in 16 out of 19 children. The 3 failures were subsequently treated with metronidazole. 2 were cured; the remaining patient did not reattend for follow-up. Metronidazole is as effective as the previously favoured combined regimen of amoebicides in children with amoebic dysentry. It is a safe and simple form of treatment.

Relapsing amoebic colitis of 12 year's standing exacerbated by corticosteroids

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