Field study of parasitic contamination of fruits, vegetables and leafy greens in the Ecuadorian Andes

Background

Raw vegetables have been considered vehicles of enteroparasites. South American countries are among the most important exporters of fresh vegetables, including Ecuador, which has a tropical climate and soils rich in organic matter that allow it to harvest throughout the year for sale to different countries. The aim of the study was to assess the occurrence of the parasitic contamination of fruits, vegetables and leafy greens grown in an agricultural area of the Ecuadorian Andes.

Methods

A cross-sectional field study was conducted with snowball sampling on 1,416 samples (516 fruits, 488 vegetables, and 412 leafy greens). Each sample were washed with water, and the resulting solution after removing the vegetables, was subjected to 24-hour sedimentation. The concentrated sediment underwent microscopic analysis.

Results

The overall positivity for parasitic contamination was 63.4%, with leafy greens having the highest contamination rate (76.9%) (P<0.0001), surpassing vegetables (67.8%) and fruits (48.4%). Cabbage (100%), onions (84%), and strawberries (60.2%) emerged as the most contaminated within their respective groups. Protozoa were more prevalent (49.6%) than helminths (15.5%) (P<0.0001). Blastocystis sp. (33.5%) ranked highest, followed by Eimeria spp. (26.3%), Entamoeba spp. (10.3%), Giardia spp. (8.3%), Balantidium spp. (6.9%), Cryptosporidium spp. (6.6%), Cyclospora spp. (4.4%), Cystoisospora spp. (0.5%), Strongylida (15.5%), and Ascaris spp. (0.4%).

Conclusions

The study reveals that vegetables and fruits for human consumption from this area of the Ecuadorian Andes are highly contaminated with various parasites, constituting a possible source of infection for humans and animals in this area, or in non-endemic areas where these products are marketed. The finding emphasizes the need for strict hygienic measures in agricultural crops, which will be properly achieved through the treatment of soil, manure and water used for cultivation.

Extracellular Cysteine Proteases of Key Intestinal Protozoan Pathogens-Factors Linked to Virulence and Pathogenicity

Intestinal diseases caused by protistan parasites of the genera Giardia (giardiasis), Entamoeba (amoebiasis), Cryptosporidium (cryptosporidiosis) and Blastocystis (blastocystosis) represent a major burden in human and animal populations worldwide due to the severity of diarrhea and/or inflammation in susceptible hosts. These pathogens interact with epithelial cells, promoting increased paracellular permeability and enterocyte cell death (mainly apoptosis), which precede physiological and immunological disorders. Some cell-surface-anchored and molecules secreted from these parasites function as virulence markers, of which peptide hydrolases, particularly cysteine proteases (CPs), are abundant and have versatile lytic activities. Upon secretion, CPs can affect host tissues and immune responses beyond the site of parasite colonization, thereby increasing the pathogens' virulence. The four intestinal protists considered here are known to secrete predominantly clan A (C1- and C2-type) CPs, some of which have been characterized. CPs of Giardia duodenalis (e.g., Giardipain-1) and Entamoeba histolytica (EhCPs 1-6 and EhCP112) degrade mucin and villin, cause damage to intercellular junction proteins, induce apoptosis in epithelial cells and degrade immunoglobulins, cytokines and defensins. In Cryptosporidium, five Cryptopains are encoded in its genome, but only Cryptopains 4 and 5 are likely secreted. In Blastocystis sp., a legumain-activated CP, called Blastopain-1, and legumain itself have been detected in the extracellular medium, and the former has similar adverse effects on epithelial integrity and enterocyte survival. Due to their different functions, these enzymes could represent novel drug targets. Indeed, some promising results with CP inhibitors, such as vinyl sulfones (K11777 and WRR605), the garlic derivative, allicin, and purified amoebic CPs have been obtained in experimental models, suggesting that these enzymes might be useful drug targets.

What about the Cytoskeletal and Related Proteins of Tapeworms in the Host's Immune Response? An Integrative Overview

Recent advances have increased our understanding of the molecular machinery in the cytoskeleton of mammalian cells, in contrast to the case of tapeworm parasites, where cytoskeleton remains poorly characterized. The pertinence of a better knowledge of the tapeworm cytoskeleton is linked to the medical importance of these parasitic diseases in humans and animal stock. Moreover, its study could offer new possibilities for the development of more effective anti-parasitic drugs, as well as better strategies for their surveillance, prevention, and control. In the present review, we compile the results of recent experiments on the cytoskeleton of these parasites and analyze how these novel findings might trigger the development of new drugs or the redesign of those currently used in addition to supporting their use as biomarkers in cutting-edge diagnostic tests.

Extracellular vesicles in COVID-19 prognosis, treatment, and vaccination: an update

The lethality of the COVID 19 pandemic became the trigger for one of the most meteoric races on record in the search for strategies of disease control. Those include development of rapid and sensitive diagnostic methods, therapies to treat severe cases, and development of anti-SARS-CoV-2 vaccines, the latter responsible for the current relative control of the disease. However, the commercially available vaccines are still far from conferring protection against acquiring the infection, so the development of more efficient vaccines that can cut the transmission of the variants of concerns that currently predominate and those that will emerge is a prevailing need. On the other hand, considering that COVID 19 is here to stay, the development of new diagnosis and treatment strategies is also desirable. In this sense, there has recently been a great interest in taking advantage of the benefits offered by extracellular vesicles (EVs), membrane structures of nanoscale size that carry information between cells participating in this manner in many physiological homeostatic and pathological processes. The interest has been focused on the fact that EVs are relatively easy to obtain and manipulate, allowing the design of natural nanocarriers that deliver molecules of interest, as well as the information about the pathogens, which can be exploited for the aforementioned purposes. Studies have shown that infection with SARS-CoV-2 induces the release of EVs from different sources, including platelets, and that their increase in blood, as well as some of their markers, could be used as a prognosis of disease severity. Likewise, EVs from different sources are being used as the ideal carriers for delivering active molecules and drugs to treat the disease, as well as vaccine antigens. In this review, we describe the progress that has been made in these three years of pandemic regarding the use of EVs for diagnosis, treatment, and vaccination against SARS-CoV-2 infection. KEY POINTS: • Covid-19 still requires more effective and specific treatments and vaccines. • The use of extracellular vesicles is emerging as an option with multiple advantages. • Association of EVs with COVID 19 and engineered EVs for its control are presented.

Potent Anti-amoebic Effects of Ibogaine, Voacangine and the Root Bark Alkaloid Fraction of Tabernaemontana arborea

Plants of Tabernaemontana species have several pharmacological activities including antimicrobial effects. Amoebiasis continues to be a public health problem, with increasing evidence of resistance to metronidazole. In this study, we assessed the effect of the alkaloid fraction of T. arborea root bark and the alkaloids ibogaine and voacangine on the viability and infectivity of Entamoeba histolytica trophozoites. Cultures were exposed to 0.1 - 10 µg/mL for 24, 48 and 72 h, and viability was then determined using a tetrazolium dye reduction assay and type of cellular death analyzed by flow cytometry. Results showed that the alkaloid fraction, but mainly ibogaine and voacangine alkaloids, exhibited potent dose-dependent anti-amoebic activity at 24 h post-exposure (IC₅₀ 4.5 and 8.1 µM, respectively), comparable to metronidazole (IC₅₀ 6.8 µM). However, the effect decreased after 48 and 72 h of exposure to concentrations below 10 µg/mL, suggesting that the alkaloids probably were catabolized to less active derivatives by the trophozoites. The treatment of trophozoites with the IC_50 s for 24 h induced significant morphological changes in the trophozoites, slight increase in granularity, and death by apoptonecrosis. The capacity of T. arborea alkaloids to inhibit the development of amoebic liver abscesses in hamsters was evaluated. Results showed that even when the treatments reduced the number of amoebic trophozoites in tissue sections of livers, they were unable to limit the formation of abscesses, suggesting their rapid processing to inactive metabolites. This work leaves open the possibility of using Tabernaemontana alkaloids as a new alternative for amoebiasis control.

Immunomodulatory effect of extracellular vesicles from Entamoeba histolytica trophozoites: Regulation of NETs and respiratory burst during confrontation with human neutrophils

Parasites release extracellular vesicles (EVs) which, in some cases, modulate the host's immune response contributing to the establishment of the infection. In this work we have isolated and characterized the EVs released by trophozoites of the human protozoan parasite Entamoeba histolytica, the causal agent of amoebiasis, when alone or in coculture with human neutrophils, and determined their effect on neutrophil NETs and ROS production. Nanoparticle tracking analysis showed that amoebic EVs are variable in size, ranging from less than 50 nm to nearly 600 nm in diameter (average of 167 nm), whereas neutrophil EVs are more uniform in size, with an average of 136 nm. In cocultures amoeba:neutrophil (1:100) most EVs are 98 nm in size, which is the typical size of exosomes. EVs from amoebae and neutrophils showed almost equal levels of ROS, which were considerably increased in EVs from cocultures. Uptake of amoebic EVs by neutrophils was demonstrated by fluorescence and resulted in a significant reduction in the oxidative burst and NET release triggered by PMA, ionophore A23187, or the amoebae itself used as stimuli. Interestingly, uptake of EVs from cocultures did not affect ROS production, but instead caused a greater delay in the onset of NETs release and in their quantity. A comparative proteomic analysis between the EVs of amoebae and neutrophils separately vs the cocultures showed a similar distribution of protein categories in the GO analysis, but differences in the expression and abundance of proteins such as the N-acetyl-D-galactosamine (GalNAc) inhibitable surface lectin and calreticulin in amoeba EVs, and various antimicrobial molecules in neutrophil EVs, such as lactoferrin and myeloperoxidase. These results highlight the importance of EVs in the immunomodulatory effects exerted by amoeba on human neutrophils.

Towards the development of an epitope-focused vaccine for SARS-CoV-2

The rapid spread of COVID-19 on all continents and the mortality induced by SARS-CoV-2 virus, the cause of the pandemic coronavirus disease 2019 (COVID-19) has motivated an unprecedented effort for vaccine development. Inactivated viruses as well as vaccines focused on the partial or total sequence of the Spike protein using different novel platforms such us RNA, DNA, proteins, and non-replicating viral vectors have been developed. The high global need for vaccines, now and in the future, and the emergence of new variants of concern still requires development of accessible vaccines that can be adapted according to the most prevalent variants in the respective regions. Here, we describe the immunogenic properties of a group of theoretically predicted RBD peptides to be used as the first step towards the development of an effective, safe and low-cost epitope-focused vaccine. One of the tested peptides named P5, proved to be safe and immunogenic. Subcutaneous administration of the peptide, formulated with alumina, induced high levels of specific IgG antibodies in mice and hamsters, as well as an increase of IFN-γ expression by CD8+ T cells in C57 and BALB/c mice upon in vitro stimulation with P5. Neutralizing titers of anti-P5 antibodies, however, were disappointingly low, a deficiency that we will attempt to resolve by the inclusion of additional immunogenic epitopes to P5. The safety and immunogenicity data reported in this study support the use of this peptide as a starting point for the design of an epitope restricted vaccine.

An RBD-Based Diagnostic Method Useful for the Surveillance of Protective Immunity against SARS-CoV-2 in the Population

After more than two years, the COVID-19 pandemic is still ongoing and evolving all over the world; human herd immunity against SARS-CoV-2 increases either by infection or by unprecedented mass vaccination. A substantial change in population immunity is expected to contribute to the control of transmission. It is essential to monitor the extension and duration of the population’s immunity to support the decisions of health authorities in each region and country, directed to chart the progressive return to normality. For this purpose, the availability of simple and cheap methods to monitor the levels of relevant antibodies in the population is a widespread necessity. Here, we describe the development of an RBD-based ELISA for the detection of specific antibodies in large numbers of samples. The recombinant expression of an RBD-poly-His fragment was carried out using either bacterial or eukaryotic cells in in vitro culture. After affinity chromatography purification, the performance of both recombinant products was compared by ELISA in similar trials. Our results showed that eukaryotic RBD increased the sensitivity of the assay. Interestingly, our results also support a correlation of the eukaryotic RBD-based ELISA with other assays aimed to test for neutralizing antibodies, which suggests that it provides an indication of protective immunity against SARS-CoV-2.

A class I histone deacetylase is implicated in the encystation of Entamoeba invadens

Epigenetic mechanisms such as histone acetylation and deacetylation participate in regulation of the genes involved in encystation of Entamoeba invadens. However, the histones and target residues involved, and whether the acetylation and deacetylation of the histones leads to the regulation of gene expression associated with the encystation of this parasite, remain unknown. In this study, we found that E. invadens histone H4 is acetylated in both stages of the parasite and is more highly acetylated during the trophozoite stage than in the cyst. Histone hyperacetylation induced by Trichostatin A negatively affects the encystation of E. invadens, and this inhibition is associated with the downregulation of the expression of genes implicated in the synthesis of chitin, polyamines, gamma-aminobutyric acid pathways and cyst wall proteins, all of which are important in the formation of cysts. Finally, in silico analysis and activity assays suggest that a class I histone deacetylase (EiHDAC3) could be involved in control of the expression of a subset of genes that are important in several pathways during encystation. Therefore, the identification of enzymes that acetylate and/or deacetylate histones that control encystation in E. invadens could be a promising therapeutic target for preventing transmission of other amoebic parasites such as E. histolytica, the causative agent of amoebiasis in humans.

Anti-amoebic Activity of Leaf Extracts and Aporphine Alkaloids Obtained from Annona purpurea

Annona purpurea has been traditionally used by indigenous and socioeconomically disadvantaged people to treat infectious and parasitic diseases, including amoebiasis. The goal of this study was to assess the effect of a crude methanolic extract, an alkaloid extract, and aporphine alkaloids from leaves of A. purpurea on the viability of Entamoeba histolytica trophozoite cultures and to identify the mechanism of action. Different concentrations of the extracts and alkaloids purpureine (1: ), 3-hydroxyglaucine (2: ), norpurpureine (3: ) glaziovine (4: ), and oxopurpureine (5: ) were added to the cultures, and dead parasites were counted after 24 h using a tetrazolium dye reduction assay and analyzed by flow cytometry. The crude extract did not affect the viability of amoebae, but the alkaloid extract and the derived alkaloid glaziovine (4: ) had important anti-amoebic activity with an IC₅₀ of 33.5 µM compared to that shown by metronidazole (6.8 µM). The treatments induced significant morphological changes in the trophozoites, and most parasites killed by the alkaloid extract were positive for Annexin V, suggesting that apoptosis was the main mechanism of action. In contrast, glaziovine (4: ) induced less apoptosis with more amoebic lysis. This study supports the idea that aporphine alkaloids from A. purpurea, mainly (+)-(R)-glaziovine (4: ), could contribute to the development of new formulations for the treatment of amoebiasis. In addition, X-ray diffraction structural analysis and complete ¹H and ¹³C NMR assignments of (+)-(R)-glaziovine (4: ) were performed and reported for the first time.

Lactoferrin: Balancing Ups and Downs of Inflammation Due to Microbial Infections

Lactoferrin (Lf) is a glycoprotein of the primary innate immune-defense system of mammals present in milk and other mucosal secretions. This protein of the transferrin family has broad antimicrobial properties by depriving pathogens from iron, or disrupting their plasma membranes through its highly cationic charge. Noteworthy, Lf also exhibits immunomodulatory activities performing up- and down-regulation of innate and adaptive immune cells, contributing to the homeostasis in mucosal surfaces exposed to myriad of microbial agents, such as the gastrointestinal and respiratory tracts. Although the inflammatory process is essential for the control of invasive infectious agents, the development of an exacerbated or chronic inflammation results in tissue damage with life-threatening consequences. In this review, we highlight recent findings in in vitro and in vivo models of the gut, lung, oral cavity, mammary gland, and liver infections that provide experimental evidence supporting the therapeutic role of human and bovine Lf in promoting some parameters of inflammation and protecting against the deleterious effects of bacterial, viral, fungal and protozoan-associated inflammation. Thus, this new knowledge of Lf immunomodulation paves the way to more effective design of treatments that include native or synthetic Lf derivatives, which may be useful to reduce immune-mediated tissue damage in infectious diseases.

Immunodiagnosis of porcine cysticercosis: identification of candidate antigens through immunoproteomics

Cysticercosis, caused by the larval stage of Taenia solium, is a zoonotic disease affecting pigs and humans that is endemic to developing countries in Latin America, Africa and South East Asia. The prevalence of infection in pigs, the intermediate host for T. solium, has been used as an indicator for monitoring disease transmission in endemic areas. However, accurate and specific diagnostic tools for porcine cysticercosis remain to be established. Using proteomic approaches and the T. solium genome sequence, seven antigens were identified as specific for porcine cysticercosis, namely, tropomyosin 2, alpha-1 tubulin, beta-tubulin 2, annexin B1, small heat-shock protein, 14-3-3 protein, and cAMP-dependent protein kinase. None of these proteins were cross-reactive when tested with sera from pigs infected with Ascaris spp., Cysticercus tenuicollis and hydatid cysts of Echinococcus spp. or with serum from a Taenia saginata-infected cow. Comparison with orthologues, indicated that the amino acid sequences of annexin B1 and cAMP-dependent protein kinase possessed highly specific regions, which might make them suitable candidates for development of a specific diagnostic assay for porcine cysticercosis.

Regulation of intestinal immune response by selective removal of the anterior, posterior, or entire pituitary gland in Trichinella spiralis infected golden hamsters

The influence of anterior pituitary hormones on the gastrointestinal tract of humans and animals has been previously reported. Hypophysectomy (HYPOX) in the rat causes atrophy of the intestinal mucosa, and reduction of gastric secretion and intestinal absorption, as well as increased susceptibility to bacterial and viral infections. However, to our knowledge, no findings have been published concerning the immune response following HYPOX during worm infection, particularly that which is caused by the nematode Trichinella spiralis. The aim of this work was to analyze the effects of total or partial HYPOX on colonization of T. spiralis in the intestinal lumen, together with duodenal and splenic cytokine expression. Our results indicate that 5 days post infection, only neurointermediate pituitary lobectomy (NIL) reduces the number of intestinally recovered T. spiralis larvae. Using semiquantitative inmunofluorescent laser confocal microscopy, we observed that the mean intensity of all tested Th1 cytokines was markedly diminished, even in the duodenum of infected controls. In contrast, a high level of expression of these cytokines was noted in the NIL infected hamsters. Likewise, a significant decrease in the fluorescence intensity of Th2 cytokines (with the exception of IL-4) was apparent in the duodenum of control and sham infected hamsters, compared to animals with NIL surgeries, which showed an increase in the expression of IL-5 and IL-13. Histology of duodenal mucosa from NIL hamsters showed an exacerbated inflammatory infiltrate located along the lamina propria, which was related to the presence of the parasite. We conclude that hormones from each pituitary lobe affect the gastrointestinal immune responses to T. spiralis through various mechanisms.

Oral lactoferrin treatment resolves amoebic intracecal infection in C3H/HeJ mice

Entamoeba histolytica is a protozoan parasite that causes amoebiasis, an illness that affects many people around the world. We have previously reported that lactoferrin is able to kill E. histolytica in in vitro cultures. The aim of the present study was to evaluate the therapeutic effect of orally administered bovine lactoferrin in the control of intestinal amoebiasis of susceptible C3H/HeJ mice. The results showed that 20 mg lactoferrin/kg orally administered each day for 1 week was able to eliminate the infection in 63% of the mice, since neither trophozoites nor evidence of epithelial damage and (or) swelling were found in tissue sections of the cecum. The rest of the treated animals (37%) showed a decrease in trophozoite numbers and mucus secreted to the lumen, as compared with untreated and infected mice (p < 0.05). By immunohistochemistry, the profile of secreted cytokines in the cecum revealed that infected but untreated animals showed a mixed Th1/regulatory cytokines profile, whereas the cecum of mice treated (cured) showed a Th2 cytokine profile (IL-4) and expression of the multifunctional IL-6. In addition, cytokines and increasing cecal production of total IgA antibodies were found associated with little inflammation and disease control observed in the cecum of lactoferrin-treated animals. These results suggest that oral administration of lactoferrin can control intestinal amoebic infection probably by killing amoebas or favoring their removal and reestablish the antiinflammatory intestinal environment.

Progesterone induces mucosal immunity in a rodent model of human taeniosis by Taenia solium

More than one quarter of human world's population is exposed to intestinal helminth parasites. The Taenia solium tapeworm carrier is the main risk factor in the transmission of both human neurocysticercosis and porcine cysticercosis. Sex steroids play an important role during T. solium infection, particularly progesterone has been proposed as a key immunomodulatory hormone involved in susceptibility to human taeniosis in woman and cysticercosis in pregnant pigs. Thus, we evaluated the effect of progesterone administration upon the experimental taeniosis in golden hamsters (Mesocricetus auratus). Intact female adult hamsters were randomly divided into 3 groups: progesterone-subcutaneously treated; olive oil-treated as the vehicle group; and untreated controls. Animals were treated every other day during 4 weeks. After 2 weeks of treatment, all hamsters were orally infected with 4 viable T. solium cysticerci. After 2 weeks post infection, progesterone-treated hamsters showed reduction in adult worm recovery by 80%, compared to both vehicle-treated and non-manipulated infected animals. In contrast to control and vehicle groups, progesterone treatment diminished tapeworm length by 75% and increased proliferation rate of leukocytes from spleen and mesenteric lymph nodes of infected hamsters by 5-fold. The latter exhibited high expression levels of IL-4, IL-6 and TNF-α at the duodenal mucosa, accompanied with polymorphonuclear leukocytes infiltration. These results support that progesterone protects hamsters from the T. solium adult tapeworm establishment by improving the intestinal mucosal immunity, suggesting a potential use of analogues of this hormone as novel inductors of the gut immune response against intestinal helminth infections and probably other bowel-related disorders.

Mucosal delivery of ACNPV baculovirus driving expression of the Gal-lectin LC3 fragment confers protection against amoebic liver abscess in hamster

Mucosal vaccination against amoebiasis using the Gal-lectin of E. histolytica has been proposed as one of the leading strategies for controlling this human disease. However, most mucosal adjuvants used are toxic and the identification of safe delivery systems is necessary. Here, we evaluate the potential of a recombinant Autographa californica baculovirus driving the expression of the LC3 fragment of the Gal-lectin to confer protection against amoebic liver abscess (ALA) in hamsters following oral or nasal immunization. Hamsters immunized by oral route showed complete absence (57.9%) or partial development (21%) of ALA, resulting in some protection in 78.9% of animals when compared with the wild type baculovirus and sham control groups. In contrast, nasal immunization conferred only 21% of protection efficacy. Levels of ALA protection showed lineal correlation with the development of an anti-amoebic cellular immune response evaluated in spleens, but not with the induction of seric IgG anti-amoeba antibodies. These results suggest that baculovirus driving the expression of E. histolytica vaccine candidate antigens is useful for inducing protective cellular and humoral immune responses following oral immunization, and therefore it could be used as a system for mucosal delivery of an anti-amoebic vaccine.

Parasiticidal effect of 16alpha-bromoepiandrosterone (EpiBr) in amoebiasis and cysticercosis

The effect of the dehydroepiandrosterone analog 16alpha-bromoepiandrosterone (EpiBr) was tested on the tapeworm Taenia crassiceps and the protist Entamoeba histolytica, both in vivo and in vitro. Administration of EpiBr prior to infection with cysticerci in mice reduced the parasite load by 50% compared with controls. EpiBr treatment induced 20% reduction on the development of amoebic liver abscesses in hamsters. In vitro treatment of T. crassiceps and E. histolytica cultures with EpiBr, reduced reproduction, motility and viability in a dose- and time-dependent fashion. These results leave open the possibility of assessing the potential of this hormonal analog as a possible anti-parasite drug, including cysticercosis and amoebiasis.

Protection against murine intestinal amoebiasis induced by oral immunization with the 29 kDa antigen of Entamoeba histolytica and cholera toxin

Entamoeba histolytica antigens recognized by salivary IgA from infected patients include the 29 kDa antigen (Eh29), an alkyl hydroperoxide reductase. Here, we investigate the potential of recombinant Eh29 and an Eh29-cholera toxin subunit B (CTxB) fusion protein to confer protection against intestinal amoebiasis after oral immunization. The purified Eh29-CTxB fusion retained the critical ability to bind ganglioside GM(1), as determined by ELISA. Oral immunization of C3H/HeJ mice with Eh29 administered in combination with a subclinical dose of whole cholera toxin, but not as an Eh29-CTxB fusion, induced elevated levels of intestinal IgA and serum IgG anti-Eh29 antibodies that inhibited trophozoites adherence to MDCK cell monolayers. The 80% of immunized mice seen to develop IgA and IgG immune responses showed no evidence of infection in tissue sections harvested following intracecal challenge with virulent E. histolytica trophozoites. These results suggest that Eh29 is capable of inducing protective anti-amoebic immune responses in mice following oral immunization and could be used in the development of oral vaccines against amoebiasis.

Gonadectomy inhibits development of experimental amoebic liver abscess in hamsters through downregulation of the inflammatory immune response

Incidence of amoebic liver abscess (ALA) in human males is considerably higher than in females, suggesting a role for sex hormones in this parasite infection. We describe here the effect of hamster gonadectomization on the development of ALA. After monitoring the decrease of oestradiol in females and testosterone in males to undetectable levels by ELISA and Radio Immuno Assay (RIA) in serum, hamsters were intraportally infected with Entamoeba histolytica trophozoites and killed 7 days later. ALA was absent in 50% of male and 15% of female gonadectomized (Gdx) hamsters, in comparison with 100% infection in non-Gdx controls. This protection against ALA in Gdx hamsters was concomitant to a comparatively scarce inflammatory infiltrate and necrosis surrounding clusters of trophozoites in the liver tissue, as well as to a lack of response of spleen cells to Con A, evaluated in proliferation assays. As tissue damage in ALA has been associated with a local inflammatory Th1 response, we determined the profile of response in hamsters by immunohistochemistry on liver sections. In contrast to strong Th1 responses in non-Gdx animals, Gdx females and males exhibited Th2 and Th3 profiles of cytokines, respectively, suggesting that protection against ALA following gonadectomization, could be related to downregulation of liver Th1 response during amoebic infection.

Standardization of an experimental model of human taeniosis for oral vaccination

Neurocysticercosis in humans is caused by the tapeworm Taenia solium and generates substantial morbidity in Latin America, Africa and Asia.The life cycle of T. solium includes pigs as intermediate hosts and human beings as definitive hosts. Tapeworm carriers are the main risk factor for acquiring cysticercosis in the household, thus prevention and control programs are being developed. Infected people have no symptoms, therefore are difficult to identify and treat, thus vaccination against the adult tapeworm is an alternative control measure. Since the infection occurs naturally only in human beings, experimental models have been standardized. Hamsters are believed to be good models to study the infection but they have not been properly evaluated for vaccination. Since taeniosis is gained by ingesting pork meat with cysticerci, oral vaccination was evaluated, and given that intestinal immunity is enhanced with adjuvants, cholera toxin was used, because it is one of the most potent adjuvants, in view of the fact that it increases epithelium permeability enhancing entrance of the co-administered unrelated antigens. Recombinant functional T. solium calreticulin was employed for the standardization of the methodology and the evaluation of oral vaccination. Protection was associated with the type of cysticerci and the age of the hamsters used. When reddish bigger parasites were orally introduced in hamsters as challenge, protection was around 40%, while when yellowish small parasites were used, protection increased to 100%, suggesting that the characteristics of cysticerci are determinant. Protection was gained in 9month old hamsters, but not in 3month old animals.

Antifouling activity of sessile bacilli derived from marine surfaces

Marine biofilms are a virtually untapped source of bioactive molecules that may find application as novel antifoulants in the marine paint industry. This study aimed at determining the potential of marine biofilm bacteria to produce novel biomolecules with potential application as natural antifoulants. Nine representative strains were isolated from a range of surfaces and were grown in YEB medium and harvested during the late exponential growth phase. Bacterial biomass and spent culture medium were extracted with ethanol and ethyl acetate, respectively. Extracts were assayed for their antifouling activity using two tests: (1) antimicrobial well diffusion test against a common fouling bacterium, Halomonas marina, and (2) anti-crustacean activity test using Artemia salina. Our results showed that none of the ethanolic extracts (bacterial biomass) were active in either test. In contrast, most of the organic extracts had antimicrobial activity (88%) and were toxic towards A. salina (67%). Sequencing of full 16 S ribosomal DNA analysis showed that the isolates were related to Bacillus mojavensis and Bacillus firmus. Matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF-MS) profiling of ethyl acetate extracts of culture supernatants showed that these species produce the bioactive lipopeptides surfactin A, mycosubtilin and bacillomycin D.

The role of the secretory immune response in the infection by Entamoeba histolytica

Intestinal infection with the protozoan parasite Entamoeba histolytica elicits a local immune response with rising of specific secretory IgA (sIgA) antibodies detectable in several compartments associated to mucosa. Anti-amoebic sIgA antibodies have been reported in faeces, saliva, bile and breast milk from dysenteric patients and research trying to elucidate their role in protection has recently intensified. IgA antibodies inhibit the in vitro adherence of E. histolytica trophozoites to epithelial cell monolayers by recognizing several membrane antigens, including the galactose-binding lectin (Gal-lectin), main surface molecule involved in adherence, and the serine and cystein-rich proteins, all of them potential vaccine candidates. In fact, the presence of sIgA anti-Gal lectin in faeces of patients recovered from amoebic liver abscess (ALA) was associated with immunity to E. dispar. Moreover, the combined nasal and intraperitoneal vaccination of C3H/HeJ mice with native and recombinant Gal-lectin protected mice against an intracecal challenge with virulent E. histolytica trophozoites, protection that seemed to be associated with the induction of specific intestinal sIgA antibodies. Therefore, the stimulation of intestinal secretory response by mucosal delivery of amoebic antigens has been positioned as a promising strategy for inducing protection against human amoebiasis.

Late experimental amebic liver abscess in hamster is inhibited by cyclosporine and N-acetylcysteine

During early experimental amebic liver abscess in hamsters (EALAH), acute inflammation is primarily responsible for tissue damage. However, during the late stages of this process, the relative contribution to tissue destruction of both parasite factors and host response is unknown. In the present work, the role of the cellular immune response in tissue damage during EALAH is explored by using the immunosuppressor drug cyclosporine A (CsA). CsA treatment inhibits tissue damage after 72 h (but not at 24 h). Also, many well-preserved parasite clusters with minimal or no leukocyte influx and with minimal or no tissue destruction characterize the late stage of the process (7 days). The same results are observed with the immunosuppressor tacrolimus, but not with sirolimus; the latter drug does not cause immunosuppression in hamsters. On the other hand, similar results are observed with the antioxidant and anti-inflammatory N-acetylcysteine, with minimal immunosuppression in hamsters. These results suggest that, as in the early EALAH (24 h), during the late stages of the process (7 days), inflammation is also primarily responsible for tissue damage. However, lysosomal and cationic proteins are responsible for the early lesions, whereas reactive oxygen and nitrogen species are primarily involved in late stages.

Characterization of extracellular polymers synthesized by tropical intertidal biofilm bacteria

AIM

This study was performed to determine the potential of tropical intertidal biofilm bacteria as a source of novel exopolymers (EPS).

METHODS AND RESULTS

A screening procedure was implemented to detect EPS-producing biofilm bacteria. Isolates MC3B-10 and MC6B-22, identified respectively as a Microbacterium species and Bacillus species by 16S rDNA and cellular fatty acids analyses, produced different EPS, as evidenced by colorimetric and gas chromatographic analyses. The polymer produced by isolate MC3B-10 displays significant surfactant activity, and may chelate calcium as evidenced by spectroscopic analysis.

CONCLUSIONS

Polymer MC3B-10 appears to be a glycoprotein, while EPS MC6B-22 seems to be a true polysaccharide dominated by neutral sugars but with significant concentrations of uronic acids and hexosamines. EPS MC3B-10 possesses a higher surfactant activity than that of commercial surfactants, and given its anionic nature, may chelate cations thus proving useful in bioremediation. The chemical composition of polymer MC6B-22 suggests its potential biomedical application in tissue regeneration.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report of a Microbacterium species producing EPS with surfactant properties, which expands our knowledge of the micro-organisms capable of producing these biomolecules. Furthermore, this work shows that tropical intertidal environments are a nonpreviously recognized habitat for bioprospecting EPS-producing bacteria, and that these molecules might be involved in ecological roles protecting the cells against dessication.

How protozoan parasites evade the immune response

Protozoan pathogens such as Plasmodium, Leishmania, Trypanosoma and Entamoeba are responsible for several of the most widespread and lethal human diseases. Their successful survival depends mainly on evading the host immune system by, for example, penetrating and multiplying within cells, varying their surface antigens, eliminating their protein coat, and modulating the host immune response. Immunosuppression is sometimes caused directly by parasite products and sometimes involves antigenic mimicry, which often appears in association with parasitic diseases. However, one of the most sophisticated mechanisms of evasion is the selective activation of a subset of T helper cells.

Cloning and characterization of Entamoeba histolytica antigens recognized by human secretory IgA antibodies

To identify the Entamoeba histolytica antigens capable of inducing secretory IgA (sIgA) responses in humans, a cDNA library from the strain HM1:IMSS was immuno-screened with saliva from patients with intestinal amebiasis or amebic liver abscess. Clones isolated with sIgA antibodies from patients with intestinal amebiasis corresponded to the known serine-rich protein isoform, a 29 kDa cysteine-rich protein and 1-alpha elongation factor. Clones corresponding to enolase, cyclophilin, ribosomal protein L23a, and an Hsp70 family protein were isolated with sIgA from a patient with amebic liver abscess. A glutamic acid-rich peptide (EhGARP) positive with sIgA from a patient with amebic liver abscess was also isolated; for EhGARP, no homologs were found in the protein databases. The antigens isolated are potentially useful in the development of an oral vaccine or new diagnostic tools for amebiasis.

Effect of zinc on Entamoeba histolytica pathogenicity

The present study analyzes the effects of zinc on Entamoeba histolytica activity and on its pathogenicity. Metal activity was evaluated in vitro with regard to the parasite's viability, replication, and adhesion to epithelial cells and in vivo with regard to its pathogenicity. The results obtained in vitro show that zinc at 1.0 mM concentration does not affect amebic viability; however, it does decrease amebic replication and adhesion (P < 0.001). In vivo studies performed on a model of experimental liver abscess in the hamster indicate that the intraperitoneal administration of a single dose of zinc at 48 h after the intrahepatic inoculation of amebic trophozoites significantly inhibits (P < 0.001) abscess development. The results indicate that zinc alters the functionality of the ameba in vitro as reflected by a decrease in replication and adhesion and in vivo as manifested by inhibition of amebic pathogenicity.

Secretory immune response in patients with intestinal amoebiasis

The secretory immune response in saliva from intestinal amoebiasis patients against antigens obtained from Entamoeba histolytica membranes was studied. Western blot analysis indicated that patient saliva contains secretory IgA antibodies against antigens with molecular masses ranging from 170 to 24 kDa, some of which were also recognized by saliva from healthy subjects. However, antigens of 170, 125, 46 and 37 kDa are recognized more frequently (> 90%) by the secretory IgA from patients with intestinal amoebiasis than by that from healthy subjects (< 10%).

Human secretory immunoglobulin A anti-Entamoeba histolytica antibodies inhibit adherence of amebae to MDCK cells

The presence of secretory immunoglobulin A (IgA) anti-Entamoeba histolytica antibodies in the saliva of patients with intestinal amebiasis was demonstrated by immunoblot assay, and the capacity of these antibodies to inhibit amebic adherence to a monolayer of MDCK cells was analyzed. Inhibition was due to IgA antiamebic antibodies and in part to anti-Gal-binding-lectin antibodies, as demonstrated by absorption experiments with total amebic extract and with the fraction of Gal-binding lectin. These results emphasize the relevance of secretory IgA antibodies in the phenomenon of E. histolytica adherence to epithelial cells.