Ameba-bacterium relationship in amebiasis

Enteropathogenic Escherichia coli induces Entamoeba histolytica superdiffusion movement on fibronectin by reducing traction forces

Amebiasis, caused by Entamoeba histolytica, is a global health concern, affecting millions and causing significant mortality, particularly in areas with poor sanitation. Although recent studies have examined E. histolytica's interaction with human intestinal microbes, the impact of bacterial presence on the parasite's motility, mechanical forces, and their potential role in altering invasiveness have not been fully elucidated. In this study, we utilized a micropillar-array system combined with live imaging to investigate the effects of enteropathogenic Escherichia coli on E. histolytica's motility characteristics, F-actin spatial localization, and traction force exerted on fibronectin-coated substrates. Our findings indicate that co-incubation with live enteropathogenic E. coli significantly enhances the motility of E. histolytica, as evidenced by superdiffusive movement-characterized by increased directionality and speed-resulting in broader dispersal and more extensive tissue/cell damage. This increased motility is accompanied by a reduction in F-actin-dependent traction forces and podosome-like structures on fibronectin-coated substrates, but with increased F-actin localization in the upper part of the cytoplasm. These findings highlight the role of physical interactions and cellular behaviors in modulating the parasite's virulence, providing new insights into the mechanistic basis of its pathogenicity.

Ancestral TALE homeobox protein transcription factor regulates actin dynamics and cellular activities of protozoan parasite Entamoeba invadens

Entamoeba histolytica causes invasive amoebiasis, an important neglected tropical disease with a significant global health impact. The pathogenicity and survival of E. histolytica and its reptilian equivalent, Entamoeba invadens, relies on its ability to exhibit efficient motility, evade host immune responses, and exploit host resources, all of which are governed by the actin cytoskeleton remodeling. Our study demonstrates the early origin and the regulatory role of TALE homeobox protein EiHbox1 in actin-related cellular processes. Several genes involved in different biological pathways, including actin dynamics are differentially expressed in EiHbox1 silenced cells. EiHbox1 silenced parasites showed disrupted F-actin organization and loss of cellular polarity. EiHbox1's presence in the anterior region of migrating cells further suggests its involvement in maintaining cellular polarity. Loss of polarized morphology of EiHbox1 silenced parasites leads to altered motility from fast, directionally persistent, and highly chemotactic to slow, random, and less chemotactic, which subsequently leads to defective aggregation during encystation. EiHbox1 knockdown also resulted in a significant reduction in phagocytic capacity and poor capping response. These findings highlight the importance of EiHbox1 of E. invadens in governing cellular processes crucial for their survival, pathogenicity, and evasion of the host immune system.

Utility of loop-mediated isothermal amplification as a point-of-care test in diagnosis of amoebic liver abscess

Definitive diagnosis of amoebic liver abscess is challenging owing to the unavailability of sensitive commercial point-of-care molecular tests. The primary aim of our prospective diagnostic study was to compare available laboratory methods for the diagnosis of Entamoeba histolytica in clinical samples with loop-mediated isothermal amplification. We compared deoxyribonucleic acid (DNA) analysis methods, namely, loop-mediated isothermal amplification and reverse transcriptase polymerase chain reaction and enzyme-linked immunosorbent assay (ELISA) using pus, stool and blood samples from 200 patients with clinical and radiological diagnosis of amoebic liver abscess. Loop-mediated isothermal amplification had significantly higher sensitivity (88%) as compared to reverse transcriptase polymerase chain reaction (64%) and excellent specificity (100%).

Queuine Is a Nutritional Regulator of Entamoeba histolytica Response to Oxidative Stress and a Virulence Attenuator

Entamoeba histolytica is a unicellular parasite that causes amebiasis. The parasite resides in the colon and feeds on the colonic microbiota.

Queuosine is a naturally occurring modified ribonucleoside found in the first position of the anticodon of the transfer RNAs for Asp, Asn, His, and Tyr. Eukaryotes lack pathways to synthesize queuine, the nucleobase precursor to queuosine, and must obtain it from diet or gut microbiota. Here, we describe the effects of queuine on the physiology of the eukaryotic parasite Entamoeba histolytica, the causative agent of amebic dysentery. Queuine is efficiently incorporated into E. histolytica tRNAs by a tRNA-guanine transglycosylase (EhTGT) and this incorporation stimulates the methylation of C38 in tRNAGUCAsp. Queuine protects the parasite against oxidative stress (OS) and antagonizes the negative effect that oxidation has on translation by inducing the expression of genes involved in the OS response, such as heat shock protein 70 (Hsp70), antioxidant enzymes, and enzymes involved in DNA repair. On the other hand, queuine impairs E. histolytica virulence by downregulating the expression of genes previously associated with virulence, including cysteine proteases, cytoskeletal proteins, and small GTPases. Silencing of EhTGT prevents incorporation of queuine into tRNAs and strongly impairs methylation of C38 in tRNAGUCAsp, parasite growth, resistance to OS, and cytopathic activity. Overall, our data reveal that queuine plays a dual role in promoting OS resistance and reducing parasite virulence.

Bacteriomic Profiling of Branchial Lesions Induced by Neoparamoeba perurans Challenge Reveals Commensal Dysbiosis and an Association with Tenacibaculum dicentrarchi in AGD-Affected Atlantic Salmon (Salmo salar L.)

Amoebic gill disease is a parasitic condition that commonly affects marine farmed Atlantic salmon. The causative agent, Neoparamoeba perurans, induces a marked proliferation of the gill mucosa and focal superficial necrosis upon branchial lesions. The effect that amoebic branchialitis has upon gill associated commensal bacteria is unknown. A 16S rRNA sequencing approach was employed to profile changes in bacterial community composition, within amoebic gill disease (AGD)-affected and non-affected gill tissue. The bacterial diversity of biopsies with and without diseased tissue was significantly lower in the AGD-affected fish compared to uninfected fish. Furthermore, within the AGD-affected tissue, lesions appeared to contain a significantly higher abundance of the Flavobacterium, Tenacibaculum dicentrarchi compared to adjunct unaffected tissues. Quantitative PCR specific to both N. perurans and T. dicentrarchi was used to further examine the co-abundance of these known fish pathogens. A moderate positive correlation between these pathogens was observed. Taken together, the present study sheds new light on the complex interaction between the host, parasite and bacterial communities during AGD progression. The role that T. dicentrarchi may play in this complex relationship requires further investigation.

Swine multifocal ulcerative colitis and crypt abscesses associated with Entamoeba polecki subtype 3 and Salmonella Typhimurium

Piglets aged approximately 50 days exhibited diarrhea and wasting. Multiple white foci were detected in the colon of a dead piglet; histopathological findings revealed multifocal ulcers and crypt abscesses with Entamoeba trophozoites and gram-negative bacilli in the piglet. These pathogens were identified as Entamoeba polecki subtype 3 and Salmonella enterica serovar Typhimurium, respectively. Numerous E. polecki subtype 3 trophozoites were located on the edge of the ulcerative and necrotic lesions in the lamina propria. Crypt abscesses were associated with S. Typhimurium. These results suggest that E. polecki subtype 3 caused multifocal ulcerative colitis accompanied by crypt abscesses with S. Typhimurium in the piglet. This study is the first report of colitis with E. polecki subtype 3 and S. Typhimurium coinfection.

Intestinal amoebiasis: 160 years of its first detection and still remains as a health problem in developing countries

Amoebiasis is a parasitic disease caused by Entamoeba histolytica (E. histolytica), an extracellular enteric protozoan. This infection mainly affects people from developing countries with limited hygiene conditions, where it is endemic. Infective cysts are transmitted by the fecal-oral route, excysting in the terminal ileum and producing invasive trophozoites (amoebae). E. histolytica mainly lives in the large intestine without causing symptoms; however, possibly as a result of so far unknown signals, the amoebae invade the mucosa and epithelium causing intestinal amoebiasis. E. histolytica possesses different mechanisms of pathogenicity for the adherence to the intestinal epithelium and for degrading extracellular matrix proteins, producing tissue lesions that progress to abscesses and a host acute inflammatory response. Much information has been obtained regarding the virulence factors, metabolism, mechanisms of pathogenicity, and the host immune response against this parasite; in addition, alternative treatments to metronidazole are continually emerging. An accesible and low-cost diagnostic method that can distinguish E. histolytica from the most nonpathogenic amoebae and an effective vaccine are necessary for protecting against amoebiasis. However, research about the disease and its prevention has been a challenge due to the relationship between E. histolytica and the host during the distinct stages of the disease is multifaceted. In this review, we analyze the interaction between the parasite, the human host, and the colon microbiota or pathogenic microorganisms, which together give rise to intestinal amoebiasis.

Prevalence of cases of amebic liver abscess in a tertiary care centre in India: A study on risk factors, associated microflora and strain variation of Entamoeba histolytica

BACKGROUND

Amebiasis, caused by Entamoeba histolytica (E. histolytica), is a significant cause of morbidity and mortality in developing countries. Mortality due to amebiasis is mostly by extra intestinal infections, amebic liver abscess being the most common one. This study was conducted to determine the current epidemiological status, risk factors, associated microflora and strain variation of E. histolytica causing liver abscesses.

METHODS/FINDINGS

A total of 115 liver abscess cases comprising of 107 (93%) males and 8 (6.9%) females were included in the study. Microscopic examination of pus samples from the abscesses and species discrimination using nested multiplex PCR showed the presence of E. histolytica in 101 (87.5%) cases. Data collected by face to face interviews using a pre tested questionnaire suggested intake of untreated drinking water (ORs: 6.4, p = 0.002), habit of alcohol consumption (ORs: 4.0, p = 0.019) and lack of urban services (ORs: 0.08, p = 0.017) to be major risk factors associated with E. histolytica infections. The study of associated bacterial flora through aerobic culture of liver aspirates and conventional PCR for detection of anaerobes revealed the presence of Fusobacterium (19, 25.5%), Peptococcus (19, 25.5%), Prevotella (18, 24.3%), Bacteroides (8, 10.8%), Staphylococcus aureus (3, 4%), Escherichia coli (2, 2.7%), Peptostreptococcus (2, 2.7%), Clostridium (2, 2.7%) and Klebsiella pneumoniae (1, 1.3%). Further to study the clonality, genotyping of E. histolytica targeting six tRNA-linked polymorphic STR loci (A-L, D-A, N-K, R-R, STGA -D and S-Q) was carried out which showed the presence of 89 different genotypes in the liver aspirate samples.

CONCLUSION

The findings highlight the high prevalence of genetically diverse E. histolytica from the liver abscess cases in this geographical region. Low socio-economic status and habit of alcohol consumption were important predictors of amebic liver abscess.

Cross-Domain and Viral Interactions in the Microbiome

The importance of the microbiome to human health is increasingly recognized and has become a major focus of recent research. However, much of the work has focused on a few aspects, particularly the bacterial component of the microbiome, most frequently in the gastrointestinal tract. Yet humans and other animals can be colonized by a wide array of organisms spanning all domains of life, including bacteria and archaea, unicellular eukaryotes such as fungi, multicellular eukaryotes such as helminths, and viruses. As they share the same host niches, they can compete with, synergize with, and antagonize each other, with potential impacts on their host. Here, we discuss these major groups making up the human microbiome, with a focus on how they interact with each other and their multicellular host.

Phagocytosis of Gut Bacteria by Entamoeba histolytica

The protist parasite Entamoeba histolytica causes amoebiasis, a major public health problem in developing countries. Only a small fraction of patients infected with the parasite display invasive disease involving colon or extra intestinal tissues such as liver. E. histolytica exists as two distinct forms, cysts, the infective form, and trophozoites, that are responsible for disease pathology. The latter multiply in the large intestine occasionally causing disease. The large intestine in humans is populated by a number of different bacterial communities and amoebic cells grow in their midst using some as food material. Several studies have shown relationship between bacteria and E. histolytica growth and virulence. However, an understanding of this relationship in human gut environment is not clear. We have investigated the possibility that there may be specific interaction of amoeba with different bacteria present in the gut environment by using a metagenomic pipe line. This was done by incubating bacteria isolated from human fecal material with E. histolytica and then identifying the bacterial population isolated from amoebic cells using a rRNA based metagenomic approach. Our results show that the parasite prefers a few bacterial species. One of these species is Lactobacillus ruminus which has never shown to be associated with E. histolytica.

Utilization of Different Omic Approaches to Unravel Stress Response Mechanisms in the Parasite Entamoeba histolytica

During its life cycle, the unicellular parasite Entamoeba histolytica is challenged by a wide variety of environmental stresses, such as fluctuation in glucose concentration, changes in gut microbiota composition, and the release of oxidative and nitrosative species from neutrophils and macrophages. The best mode of survival for this parasite is to continuously adapt itself to the dynamic environment of the host. Our ability to study the stress-induced responses and adaptive mechanisms of this parasite has been transformed through the development of genomics, proteomics or metabolomics (omics sciences). These studies provide insights into different facets of the parasite's behavior in the host. However, there is a dire need for multi-omics data integration to better understand its pathogenic nature, ultimately paving the way to identify new chemotherapeutic targets against amebiasis. This review provides an integration of the most relevant omics information on the mechanisms that are used by E. histolytica to resist environmental stresses.

Human Intestinal Microbiota: Interaction Between Parasites and the Host Immune Response

The human gut is a highly complex ecosystem with an extensive microbial community, and the influence of the intestinal microbiota reaches the entire host organism. For example, the microbiome regulates fat storage, stimulates or renews epithelial cells, and influences the development and maturation of the brain and the immune system. Intestinal microbes can protect against infection by pathogenic bacteria, viruses, fungi and parasites. Hence, the maintenance of homeostasis between the gut microbiota and the rest of the body is crucial for health, with dysbiosis affecting disease. This review focuses on intestinal protozoa, especially those still representing a public health problem in Mexico, and their interactions with the microbiome and the host. The decrease in prevalence of intestinal helminthes in humans left a vacant ecological niche that was quickly occupied by protozoa. Although the mechanisms governing the interaction between intestinal microbiota and protozoa are poorly understood, it is known that the composition of the intestinal bacterial populations modulates the progression of protozoan infection and the outcome of parasitic disease. Most reports on the complex interactions between intestinal bacteria, protozoa and the immune system emphasize the protective role of the microbiota against protozoan infection. Insights into such protection may facilitate the manipulation of microbiota components to prevent and treat intestinal protozoan infections. Here we discuss recent findings about the immunoregulatory effect of intestinal microbiota with regards to intestinal colonization by protozoa, focusing on infections by Entamoeba histolytica, Blastocystis spp, Giardia duodenalis, Toxoplasma gondii and Cryptosporidium parvum. The possible consequences of the microbiota on parasitic, allergic and autoimmune disorders are also considered.

Analysis of the Bacterial Diversity in Liver Abscess: Differences Between Pyogenic and Amebic Abscesses

Several recent studies have demonstrated that virulence in Entamoeba histolytica is triggered in the presence of both pathogenic and nonpathogenic bacteria species using in vitro and in vivo experimental animal models. In this study, we examined samples aspirated from abscess material obtained from patients who were clinically diagnosed with amebic liver abscess (ALA) or pyogenic liver abscess (PLA). To determine the diversity of bacterial species in the abscesses, we performed partial 16S rRNA gene sequencing. In addition, the E. histolytica and Entamoeba dispar species were genotyped using tRNA-linked short tandem repeats as specific molecular markers. The association between clinical data and bacterial and parasite genotypes were examined through a correspondence analysis. The results showed the presence of numerous bacterial groups. These taxonomic groups constitute common members of the gut microbiota, although all of the detected bacterial species have a close phylogenetic relationship with bacterial pathogens. Furthermore, some patients clinically diagnosed with PLA and ALA were coinfected with E. dispar or E. histolytica, which suggests that the virulence of these parasites increased in the presence of bacteria. However, no specific bacterial groups were associated with this effect. Together, our results suggest a nonspecific mechanism of virulence modulation by bacteria in Entamoeba.

Single Dose Treatments in Tropical Infectious Diarrhoea

Single dose treatments have the important advantages of simple administration, excellent compliance, short-lived side effects (if any) and short period of drug pressure. However, drugs used for single dose treatments must possess important characteristics, namely, long half-life, effective concentration in tissues over a long period, and low toxicity. In tropical medicine, such drugs are an important advance in the treatment of malaria (mefloquine and halofantrine), schistosomiasis (praziquantel and metrifonate), filariasis (ivermectin), and genitourinary tract and intestinal infections.

Intestinal infections are one of the most frequent problems in tropical medicine. While a large number of cases of diarrhoea are of viral (rotavirus) or bacterial (Salmonella, Escherichia coli) origin, necessitating only oral rehydration, some are of parasitological origin (Giardia, Entamoeba histolytica, Strongyloides, Trichuris, Schistosoma) and can be cured by a single dose treatment (tinidazole, secnidazole, ivermectin, albendazole, praziquantel). Secnidazole is the nitroimidazole with the longest half-life and is, therefore, used in single dose treatments for Giardia, acute intestinal amoebiasis and E. histolytica cyst carriers. Single dose treatments of most intestinal parasites will be a major advance in the management of tropical infectious diarrhoea. In the next decade, opportunistic intestinal infections (Cryptosporidium, Isospora, Enterocytozoon) in AIDS patients that are refractory to treatment could be the major problem.

Succession in the gut microbiome following antibiotic and antibody therapies for Clostridium difficile

Antibiotic disruption of the intestinal microbiota may cause susceptibility to pathogens that is resolved by progressive bacterial outgrowth and colonization. Succession is central to ecological theory but not widely documented in studies of the vertebrate microbiome. Here, we study succession in the hamster gut after treatment with antibiotics and exposure to Clostridium difficile. C. difficile infection is typically lethal in hamsters, but protection can be conferred with neutralizing antibodies against the A and B toxins. We compare treatment with neutralizing monoclonal antibodies (mAb) to treatment with vancomycin, which prolongs the lives of animals but ultimately fails to protect them from death. We carried out longitudinal deep sequencing analysis and found distinctive waves of succession associated with each form of treatment. Clindamycin sensitization prior to infection was associated with the temporary suppression of the previously dominant Bacteroidales and the fungus Saccinobaculus in favor of Proteobacteria. In mAb-treated animals, C. difficile proliferated before joining Proteobacteria in giving way to re-expanding Bacteroidales and the fungus Wickerhamomyces. However, the Bacteroidales lineages returning by day 7 were different from those that were present initially, and they persisted for the duration of the experiment. Animals treated with vancomycin showed a different set of late-stage lineages that were dominated by Proteobacteria as well as increased disparity between the tissue-associated and luminal cecal communities. The control animals showed no change in their gut microbiota. These data thus suggest different patterns of ecological succession following antibiotic treatment and C. difficile infection.

Real-time analysis of gut flora in Entamoeba histolytica infected patients of Northern India

Background

Amebic dysentery is caused by the protozoan parasite Entamoeba histolytica and the ingestion of quadrinucleate cyst of E. histolytica from fecally contaminated food or water initiates infection. Excystation occurs in the lumen of small intestine, where motile and potentially invasive trophozoites germinate from cysts. The ability of trophozoites to interact and digest gut bacteria is apparently important for multiplication of the parasite and its pathogenicity; however the contribution of resident bacterial flora is not well understood. We quantified the population of Bacteroides, Bifidobacterium, Ruminococcus, Lactobacillus, Clostridium leptum subgroup, Clostridium coccoides subgroup, Eubacterium, Campylobacter, Methanobrevibacter smithii and Sulphur reducing bacteria using genus specific primers in healthy (N = 22) vs amebic patients (E. histolytica positive, N = 17) stool samples by Real-time PCR.

Results

Absolute quantification of Bacteroides (p = .001), Closrtridium coccoides subgroup (p = 0.002), Clostridium leptum subgroup (p = 0.0001), Lactobacillus (p = 0.037), Campylobacter (p = 0.0014) and Eubacterium (p = 0.038) show significant drop in their population however, significant increase in Bifdobacterium (p = 0.009) was observed where as the population of Ruminococcus (p = 0.33) remained unaltered in healthy vs amebic patients (E. histolytica positive). We also report high prevalence of nimE gene in stool samples of both healthy volunteers and amebic patients. No significant decrease in nimE gene copy number was observed before and after the treatment with antiamebic drug.

Conclusions

Our results show significant alteration in predominant gut bacteria in E. histolytica infected individuals. The frequent episodes of intestinal amoebic dysentery thus result in depletion of few predominant genera in gut that may lead to poor digestion and absorption of food in intestine. It further disturbs the homeostasis between gut epithelium and bacterial flora. The decrease in beneficial bacterial population gives way to dysbiosis of gut bacteria which may contribute to final outcome of the disease. Increase in the copy number of nimE gene harboring bacteria in our population reflects possible decrease in the availability of metronidazole drug during treatment of amoebiasis.

Novelties on amoebiasis: a neglected tropical disease

In accordance with the 1997 documents of the World Health Organization (WHO), amoebiasis is defined as the infection by the protozoan parasite Entamoeba histolytica with or without clinical manifestations. The only known natural host of E. histolytica is the human with the large intestine as major target organ. This parasite has a very simple life cycle in which the infective form is the cyst, considered a resistant form of parasite: The asymptomatic cyst passers and the intestinal amoebiasis patients are the transmitters; they excrete cysts in their feces, which can contaminate food and water sources. E. histolytica sensu stricto is the potentially pathogenic species and E. dispar is a commensal non-pathogenic Entamoeba. Both species are biochemical, immunological and genetically distinct. The knowledge of both species with different pathogenic phenotypes comes from a large scientific debate during the second half of the 20(th) century, which gave place to the rapid development of diagnostics technology based on molecular and immunological strategies. During the last ten years, knowledge of the new epidemiology of amoebiasis in different geographic endemic and non-endemic areas has been obtained by applying mostly molecular techniques. In the present work we highlight novelties on human infection and the disease that can help the general physician from both endemic and non-endemic countries in their medical practice, particularly, now that emigration is undoubtedly a global phenomenon that is modifying the previous geography of infectious diseases worldwide.

Human amebiasis: breaking the paradigm?

For over 30 years it has been established that the Entamoeba histolytica protozoan included two biologically and genetically different species, one with a pathogenic phenotype called E. histolytica and the other with a non-pathogenic phenotype called Entamoeba dispar. Both of these amoebae species can infect humans. E. histolytica has been considered as a potential pathogen that can cause serious damage to the large intestine (colitis, dysentery) and other extraintestinal organs, mainly the liver (amebic liver abscess), whereas E. dispar is a species that interacts with humans in a commensal relationship, causing no symptoms or any tissue damage. This paradigm, however, should be reconsidered or re-evaluated. In the present work, we report the detection and genotyping of E. dispar sequences of DNA obtained from patients with amebic liver abscesses, including the genotyping of an isolate obtained from a Brazilian patient with a clinical diagnosis of intestinal amebiasis that was previously characterized as an E. dispar species. The genetic diversity and phylogenetic analysis performed by our group has shown the existence of several different genotypes of E. dispar that can be associated to, or be potentiality responsible for intestinal or liver tissue damage, similar to that observed with E. histolytica.

Identification of an avirulent Entamoeba histolytica strain with unique tRNA-linked short tandem repeat markers

Highly polymorphic, non-coding short tandem repeats (STR) are scattered between the tRNA genes in Entamoeba histolytica in a unique tandemly arrayed organization. STR markers that correlate with the virulence of individual E. histolytica strains have recently been reported. Here we evaluated the usefulness of tRNA-linked STR loci as genetic markers in identifying virulent and avirulent strains of E. histolytica from 37 Japanese E. histolytica samples (12 diarrheic/dysenteric, 20 amebic liver abscess (ALA), and 5 asymptomatic cases). Twenty three genotypes, assigned by combining the STR sequence types from all 6 STR loci, were identified. One to 8 new STR sequence types per locus were also discovered. Genotypes found in asymptomatic isolates were highly polymorphic (4 out of 5 genotypes were unique to this group), while in symptomatic isolates, almost half of the genotypes were shared between diarrhea/dysentery and ALA. One asymptomatic isolate (KU27) showed unique STR patterns in 4 loci. This strain, though associated with the typical pathogenic zymodeme II, failed to induce amebic liver abscess by animal challenge, which suggests that inherently avirulent E. histolytica strains exist, that are associated with unique genotypes. Furthermore, STR genotyping and in vivo challenge of 2 other asymptomatic isolates (KU14 and KU26) verified the covert virulence of these strains.

The interplay between Entamoeba and enteropathogenic bacteria modulates epithelial cell damage

Background

Mixed intestinal infections with Entamoeba histolytica, Entamoeba dispar and bacteria with exacerbated manifestations of disease are common in regions where amoebiasis is endemic. However, amoeba–bacteria interactions remain largely unexamined.

Methodology

Trophozoites of E. histolytica and E. dispar were co-cultured with enteropathogenic bacteria strains Escherichia coli (EPEC), Shigella dysenteriae and a commensal Escherichia coli. Amoebae that phagocytosed bacteria were tested for a cytopathic effect on epithelial cell monolayers. Cysteine proteinase activity, adhesion and cell surface concentration of Gal/GalNAc lectin were analyzed in amoebae showing increased virulence. Structural and functional changes and induction of IL-8 expression were determined in epithelial cells before and after exposure to bacteria. Chemotaxis of amoebae and neutrophils to human IL-8 and conditioned culture media from epithelial cells exposed to bacteria was quantified.

Principal Findings

E. histolytica digested phagocytosed bacteria, although S. dysenteriae retained 70% viability after ingestion. Phagocytosis of pathogenic bacteria augmented the cytopathic effect of E. histolytica and increased expression of Gal/GalNAc lectin on the amoebic surface and increased cysteine proteinase activity. E. dispar remained avirulent. Adhesion of amoebae and damage to cells exposed to bacteria were increased. Additional increases were observed if amoebae had phagocytosed bacteria. Co-culture of epithelial cells with enteropathogenic bacteria disrupted monolayer permeability and induced expression of IL-8. Media from these co-cultures and human recombinant IL-8 were similarly chemotactic for neutrophils and E. histolytica.

Conclusions

Epithelial monolayers exposed to enteropathogenic bacteria become more susceptible to E. histolytica damage. At the same time, phagocytosis of pathogenic bacteria by amoebae further increased epithelial cell damage.

Significance

The in vitro system presented here provides evidence that the Entamoeba/enteropathogenic bacteria interplay modulates epithelial cell responses to the pathogens. In mixed intestinal infections, where such interactions are possible, they could influence the outcome of disease. The results offer insights to continue research on this phenomenon.

In amoebiasis, a human disease that is a serious health problem in many developing countries, efforts have been made to identify responsible factors for the tissue damage inflicted by the parasite Entamoeba histolytica. This amoeba lives in the lumen of the colon without causing damage to the intestinal mucosa, but under unknown circumstances becomes invasive, destroying the intestinal tissue. Bacteria in the intestinal flora have been proposed as inducers of higher amoebic virulence, but the causes or mechanisms responsible for the induction are still undetermined. Mixed intestinal infections with Entamoeba histolytica and enteropathogenic bacteria, showing exacerbated manifestations of disease, are common in endemic countries. We implemented an experimental system to study amoebic virulence in the presence of pathogenic bacteria and its consequences on epithelial cells. Results showed that amoebae that ingested enteropathogenic bacteria became more virulent, causing more damage to epithelial cells. Bacteria induced release of inflammatory proteins by the epithelial cells that attracted amoebae, facilitating amoebic contact to the epithelial cells and higher damage. Our results, although a first approach to this complex problem, provide insights into amoebic infections, as interplay with other pathogens apparently influences the intestinal environment, the behavior of cells involved and the manifestations of the disease.

Dynamics of endocytic traffic ofEntamoeba histolyticarevealed by confocal microscopy and flow cytometry

Entamoeba histolytica, the protozoan parasite of humans, manifests constitutive endocytosis to obtain nutrients and, when induced to express invasive behavior, as a means of ingesting and processing host cells and tissue debris. E. histolytica trophozoites were grown in liquid axenic medium that contained fluorescently labeled fluid-phase markers, so that the kinetics of uptake, the transit of loaded endosomes through the cytoplasm, and the time of release of the markers could be monitored by flow cytometry. Confocal microscopy of live trophozoites revealed uptake of fluid by avid macropinocytosis and the occurrence of fusion between young and older endosomes, as well as between pinosomes and phagosomes containing bacteria. Endosomes were rapidly acidified, then gradually neutralized; finally, indigestible material was released. Transit of endosomes containing fluid-phase markers required about 2 h. Uptake and release of fluid-phase markers were impaired by drugs that inhibited actin dynamics and actin-myosin interaction; uptake was also impaired by inhibition of PI 3-kinase. A striking feature of the trophozoites was the great heterogeneity of their endocytic behavior.

BFA-sensitive and insensitive exocytic pathways in Entamoeba histolytica trophozoites: their relationship to pathogenesis

Entamoeba histolytica manifests its pathogenicity through several cellular processes triggered by external stimuli that activate signal transduction pathways. The intense secretory activity resulting from stimulation is not correlated with a typical endoplasmic reticulum (ER) or Golgi organization, and little is known in this parasite about endocytic/exocytic pathways. The interactions of trophozoites with fibronectin (FN) and cultured mammalian cells, which elicit secretory activities, were chosen to study mechanisms that regulate cytoplamic traffic. Results showed that Brefeldin A (BFA) induced redistribution of the vesicular network recognized by antibodies against amoebic proteins PDI and ERD2. Furthermore, BFA diminished traffic to the plasma membrane of the beta1 integrin-like FN receptor and the heavy subunit of the Gal/GalNAc lectin, required for adhesion to FN and target cells, respectively. However, BFA did not prevent thiol-proteinase secretion or inhibit the traffic of de novo synthesized proteinases. These data suggest that two distinct transport systems occur in E. histolytica, one similar to classical membrane protein transport and another independent of BFA and inducible by external stimuli. Actin-myosin contractility of the cortical cytoskeleton seems necessary for the final release of exported proteinases and the proper function of the surface proteins involved in adhesion.

Early lateral transfer of genes encoding malic enzyme, acetyl-CoA synthetase and alcohol dehydrogenases from anaerobic prokaryotes to Entamoeba histolytica

The fermentation enzymes, which enable the microaerophilic protist Entamoeba histolytica to parasitize the colonic lumen and tissue abscesses, closely resemble homologues in anaerobic prokaryotes. Here, genes encoding malic enzyme and acetyl-CoA synthetase (nucleoside diphosphate forming) were cloned from E. histolytica, and their evolutionary origins, as well as those encoding two alcohol dehydrogenases (ADHE and ADH1), were inferred by means of phylogenetic reconstruction. The E. histolytica malic enzyme, which decarboxylates malate to pyruvate, closely resembles that of the archaeon Archaeoglobus fulgidus, strongly suggesting a common origin. The E. histolytica acetyl-CoA synthetase, which converts acetyl-CoA to acetate with the production of ATP, appeared to be closely related to the Plasmodium falciparum enzyme, but it was no more closely related to the Giardia lamblia acetyl-CoA synthetase than to those of archaea. Phylogenetic analyses suggested that the adh1 and adhe genes of E. histolytica and Gram-positive eubacteria share a common ancestor. Lateral transfer of genes encoding these fermentation enzymes from archaea or eubacteria to E. histolytica probably occurred early, because the sequences of the amoebic enzymes show considerable divergence from those of prokaryotes, and the amoebic genes encoding these enzymes are in the AT-rich codon usage of the parasite.

Early and late endosomal compartments of Entamoeba histolytica are enriched in cysteine proteases, acid phosphatase and several Ras-related Rab GTPases

Pure populations of early and late endosomes of Entamoeba histolytica were isolated by magnetic fractionation and characterized. It was shown that these vesicles were enriched in acid phosphatase and cysteine protease activities. An important virulence factor, a 27-kDa cysteine protease, was also enriched in early and late endosomes of E. histolytica. These data suggest that E. histolytica hydrolases reside in compartments that are part of or communicate with the endosomal pathway. To begin to identify the role of Rab GTPases in E. histolytica, an oligonucleotide approach was employed to screen an E. histolytica cDNA library for genes encoding Rab-like proteins. cDNAs encoding a Rab11-like protein (EhRab11) and a novel Rab protein (EhRabA) were isolated and characterized. The EhRab11 cDNA predicts a polypeptide of at least 206 amino acids with a molecular mass of at least 23.2 kDa. Phylogenetic analysis and alignment of EhRab11 with other Rab proteins demonstrated that EhRab11 shared significant homology at the amino acid level with Rab11-like proteins from a number of other eukaryotes, suggesting that EhRab11 is a Rab11 homolog for E. histolytica. The EhRabA clone predicts a polypeptide of 219 amino acids with a molecular mass of at least 24.5 kDa. EhRabA shared only limited homology at the amino acid level with other Rab proteins, suggesting that it is a novel member of this family of GTP-binding proteins. Finally, Western blot analysis demonstrated that EhRab11 and a previously described Rab7-like GTPase from E. histolytica was enriched in magnetically purified endosomal compartments of this organism.

Antimicrobial and cytolytic polypeptides of amoeboid protozoa--effector molecules of primitive phagocytes

Amoebae are primitive, actively phagocytosing eukaryotic cells, many of which use bacteria as a major nutrient source. One may suppose that amoebae possess an array of potent antimicrobial molecules acting in synergy to combat bacterial growth inside their phagosomes. Lysosome-like granular vesicles of Entamoeba histolytica contain a family of 77-residue peptides with a compact alpha-helical, disulfide-bonded fold. These polypeptides, named amoebapores, exhibit antibacterial and cytolytic activity by forming pores in membranes of various origin. It is of particular interest that amoebapores are structurally and functionally most similar to polypeptides of mammalian cytotoxic lymphocytes. In addition, amoebic granules contain bacteriolytic proteins with lysozyme-like properties. Some amoebic polypeptides may represent archaic analogs of effector molecules from invertebrates and vertebrates.

Chitinase secretion by encysting Entamoeba invadens and transfected Entamoeba histolytica trophozoites: localization of secretory vesicles, endoplasmic reticulum, and Golgi apparatus

Entamoeba histolytica, the protozoan parasite that phagocytoses bacteria and host cells, has a vesicle/vacuole-filled cytosol like that of macrophages. In contrast, the infectious cyst form has four nuclei and a chitin wall. Here, anti-chitinase antibodies identified hundreds of small secretory vesicles in encysting E. invadens parasites and in E. histolytica trophozoites overexpressing chitinase under an actin gene promoter. Abundant small secretory vesicles were also identified with antibodies to the surface antigen Ariel and with a fluorescent substrate of cysteine proteinases. Removal of an N-terminal signal sequence directed chitinase to the cytosol. Addition of a C-terminal KDEL peptide, identified on amebic BiP, retained chitinase in a putative endoplasmic reticulum, which was composed of a few vesicles of mixed sizes. A putative Golgi apparatus, which was Brefeldin A sensitive and composed of a few large, perinuclear vesicles, was identified with antibodies to ADP-ribosylating factor and to epsilon-COP. We conclude that the amebic secretory pathway is similar to those of other eukaryotic cells, even if its appearance is somewhat different.

Down regulation of Entamoeba histolytica virulence by monoxenic cultivation with Escherichia coli O55 is related to a decrease in expression of the light (35-kilodalton) subunit of the Gal/GalNAc lectin

Entamoeba histolytica virulence is related to a number of amebic components (lectins, cysteine proteinases, and amebapore) and host factors, such as intestinal bacterial flora. Trophozoites are selective in their interactions with bacteria, and the parasite recognition of glycoconjugates plays an important role in amebic virulence. Long-term monoxenic cultivation of pathogenic E. histolytica trophozoites, strains HK-9 or HM-1:IMSS, with Escherichia coli serotype O55, which binds strongly to the Gal/GalNAc amebic lectin, markedly reduced the trophozoites' adherence and cytopathic activity on cell monolayers of baby hamster kidney (BHK) cells. Specific probes prepared from E. histolytica lectin genes as well as antibodies directed against the light (35-kDa) and heavy (170-kDa) subunits of the Gal/GalNAc lectin revealed a decrease in the transcription and expression of the light subunit in trophozoites grown monoxenically with E. coli O55. This effect was not observed when E. histolytica was grown with E. coli 346, a mannose-binding type I pilated bacteria. Our results suggest that the light subunit of the amebic lectin is involved in the modulation of parasite adherence and cytopathic activity.

Molecular characterization of an exceptionally acidic lysozyme-like protein from the protozoon Entamoeba histolytica

The protozoan parasite Entamoeba histolytica contains a second antibacterial protein with lysozyme-like properties. The newly recognized bacteriolytic protein was purified from extracts of amoebic trophozoites to allow amino-terminal sequencing. Subsequent molecular cloning revealed that it is an isoform of the amoeba lysozyme described previously but also demonstrated a substantial sequence divergence of the two forms. As lysozymes typically are basic proteins, the novel amoebic protein differs markedly in having a pI of 4.5. There is no significant similarity of both amoeba lysozymes with any bacteriolytic protein of other organisms reported so far; however, striking sequence identity is found with predicted gene products of unknown function derived from the bacteria-feeding nematode Caenorhabditis elegans.

Involvement of p21racA, phosphoinositide 3-kinase, and vacuolar ATPase in phagocytosis of bacteria and erythrocytes by Entamoeba histolytica: suggestive evidence for coincidental evolution of amebic invasiveness

Trophozoites of Entamoeba histolytica, the protozoan parasite that causes amebic dysentery, phagocytose bacteria in the colonic lumen and erythrocytes (RBC) in host tissues. Because tissue invasion is an evolutionary dead end, it is likely that amebic pathogenicity is coincidentally selected, i.e., the same methods used to kill bacteria in the colonic lumen are used by parasites to damage host cells and cause disease. In support of this idea, the amebic lectin and pore-forming peptide are involved in binding and killing, respectively, bacteria and host epithelial cells. Here amebic phagocytosis of bacteria, RBC, and mucin-coated beads was disrupted by overexpression of E. histolytica p21(racA-V12), a ras-family protein involved in selection of sites of actin polymerization, which had been mutated to eliminate its GTPase activity. p21(racA-V12) transformants were also defective in capping and cytokinesis, while pinocytosis of fluorescent dextrans was not affected. Wortmannin, a fungal inhibitor of phosphoinositide 3-kinase, markedly inhibited phagocytosis of bacteria, RBC, and mucin-coated beads by wild-type amebae. In contrast to p21(racA-V12) overexpression, wortmannin abolished amebic pinocytosis of dextrans but had no inhibitory effects on capping. Inhibition of amebic vacuolar acidification by bafilomycin also decreased bacterial and RBC uptake. These results, which demonstrate similarities between mechanisms of phagocytosis of bacteria and RBC by amebae and macrophages, support the idea of coincidental selection of amebic genes encoding proteins that mediate destruction of host cells.

Amoebapores

The enormous cytolytic potential of Entamoeba histolytica appeals to parasitologists and immunologists because it kills target cells in a contact-dependent reaction resembling that of cytotoxic lymphocytes. In this review, Matthias Leippe summarizes what is currently known about a family of pore-forming peptides termed 'amoebapores', to which the cytolytic effect has been attributed, and describes the structural and functional properties of these potent factors, as well as their structure-activity relationships. Finally, a comparison is made with effector molecules of the mammalian defensive system.

Luminal bacteria and proteases together decrease adherence of Entamoeba histolytica trophozoites to Chinese hamster ovary epithelial cells: a novel host defence against an enteric pathogen

BACKGROUND

Factors that prevent colonic mucosal invasion by pathogenic Entamoeba histolytica are not understood. A key initial step in pathogenesis of injury induced by amoeba is adherence to target cells mediated by a surface glycoprotein lectin on E histolytica. Mucin degrading bacteria normally present in the colon lumen produce glycosidases that degrade soluble or cell surface glycoconjugates.

AIM

To determine whether glycosidases produced by mucin degrading bacteria, alone or in combination with proteases present in colon lumen, can decrease E histolytica adherence to target epithelial cells by degrading E histolytica adherence lectin.

METHODS

The effects of exposure of E histolytica trophozoites strains HM1:IMSS and 200:NIH to faecal culture supernatant fluids, culture supernatant preparations of mucin degrading bacteria, and luminal proteases on their adherence to Chinese hamster ovary (CHO) cells were determined. The amount of surface adherence lectin on E histolytica trophozoites before and after treatment with glycosidases and proteases was determined by immunofluorescence. The effect of glycosidases and proteases on purified E histolytica lectin was determined by gel electrophoresis.

RESULTS

Incubation of E histolytica with culture supernatant preparations or proteases alone did not modify their CHO cell adherence. However, 24 hour incubation of trophozoites with culture supernatant preparations together with pancreatic proteases decreased CHO cell adherence of HM1:IMSS strain by 71.1% (p < 0.001) and of 200: NIH strain by 95% (p < 0.05). Incubation of trophozoites for 24 hours with faecal extracts which contain bacterial and host hydrolases decreased the adherence of the HM1:IMSS strain by 69.2% (p < 0.01) and of the 200: NIH strain by 83.0%. Reduction of trophozoite adherence to CHO cells by hydrolases was promoted by 7.5 mM cycloheximide, and was reversible on incubation in an enzyme free medium. Decrease in CHO cell adherence of trophozoites was associated with decreased lectin on trophozoites as determined by immunofluorescence using a monoclonal antibody to the lectin. Purified lectin was degraded by the mixture of faecal culture supernant preparations and proteases, but not by either alone.

CONCLUSIONS

Mucin degrading bacterial glycosidases and colonic luminal proteases together, but not alone, degrade the key adherence lectin on E histolytica trophozoites resulting in decreased epithelial cell adherence. These in vitro findings suggest a potential novel host defence mechanism in the human colon wherein the invasiveness of a pathogen could be curtailed by the combined actions of bacterial and host hydrolases. This mechanism may be responsible for preventing mucosal invasion by pathogenic E histolytica.

Purification and molecular cloning of a major antibacterial protein of the protozoan parasite Entamoeba histolytica with lysozyme-like properties

A protein with potent antibacterial activity was purified to apparent homogeneity from pathogenic Entamoeba histolytica. It resembles lysozyme in that it is a basic protein which degrades cell walls of Micrococcus luteus, displays optimal activity at acidic pH, and shows a preference for Gram-positive bacteria. The protein has a molecular mass of approximately 23 kDa upon SDS/PAGE and is localized inside the cytoplasmic granules of the amoebae. The primary structure was elucidated by protein analysis and molecular cloning of the corresponding cDNA. It yielded a protein of 198 residues with structural similarity to the distinct class of lysozymes found in Streptomyces species and the fungus Chalaropsis.

Carbohydrate involvement in the association of a prokaryotic cell with Trichomonas vaginalis and Tritrichomonas foetus

Previous studies have shown that Trichomonas vaginalis are capable of ingesting bacteria. This observation was confirmed in the present study and extended to Tritrichomonas foetus. Using a special strain of Escherichia coli grown under conditions that produced fimbriae presenting a lectin-like molecule recognizing mannose, we showed that the bacteria attached to and were ingested by trichomonads through a mechanism involving cell-to-cell recognition. Absence of the fimbriae or addition of alpha-methyl-D-mannoside to the interaction medium blocked attachment of the bacteria to the protozoa cell surface. Ingested bacteria were later digested within the cytoplasmic vacuole.

Cloning of Entamoeba genes encoding proteolipids of putative vacuolar proton-translocating ATPases

Molecular cloning techniques were used to identify genes encoding the proteolipids of putative vacuolar proton-transporting ATPases (V-ATPases; EC 3.6.1.35) of Entamoeba histolytica (Ehvma3) and Entamoeba dispar. The Ehvma3 gene encoded a 177-amino-acid peptide, with an M(r) of 18,110, which showed extensive positional identities with peptides of E. dispar (92%), Schizosaccharomyces pombe (58%), and humans (56%).

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.

Amebiasis

Entamoeba histolytica, the causative agent of amebiasis, was first described in 1875. Although a large number of people throughout the world are infected with this organism, only a small percentage will develop clinical symptoms. Morbidity and mortality due to E. histolytica vary from area to area and person to person. Recent findings have suggested that there are pathogenic and nonpathogenic strains of E. histolytica that can be differentiated by isoenzyme (zymodeme) analysis, monoclonal antibodies, and DNA probes. Whether pathogenicity is a genotypic trait or can be changed by environmental influences has not been resolved. Exchange of genetic material between strains of amebae can influence zymodeme patterns. Currently, detection of E. histolytica infections depends on examinations for ova and parasites and on serologic tests; however, the development of monoclonal antibodies and DNA probes specific for pathogenic zymodemes may be beneficial for clinical laboratory testing and therapeutic decisions when approved tests become available. A better understanding of the mechanisms of pathogenicity at the molecular level is evolving and should promote the development of vaccines and better target selection for therapeutic agents.

Modulation of a surface antigen of Entamoeba histolytica in response to bacteria

Changes in the cell surface of Entamoeba histolytica, a human intestinal parasite and the causative agent of amebic dysentery, were examined with a monoclonal antibody, 2D7.10, which selectively recognizes carbohydrate epitopes in some axenic amebic strains. While high-level expression of this epitope was observed in axenic amebae, it was either absent or present only in small amounts in xenic amebae. Furthermore, reassociation of the axenic amebae with intestinal flora resulted in loss of the 2D7.10 epitope. Our data suggest that surface antigens of E. histolytica can be modulated in response to bacteria and may provide an explanation for the observed influence of bacteria on amebic virulence.

Variations in cytotoxicity and isoenzyme patterns of uncloned and cloned cultures of axenic Entamoeba histolytica

Five clones of axenic Entamoeba histolytica (HMI) grown as discrete colonies in semisolid agar medium were adapted in liquid medium and labelled as HMI-C121, HMI-C131, HMI-C143, HMI-C144 and HMI-C145. The clone HMI-C121 was more cytotoxic to the cultured Baby Hamster Kidney (BHK) cells while all other clones were significantly (P less than 0.001) less cytotoxic as compared to the cloned HMI-C121 and uncloned E. histolytica (HMI). The uncloned Indian axenic E. histolytica (KCG:0986:11) as well as E. histolytica (NIH:200) cultures were significantly (P less than 0.001) less cytotoxic to cultured BHK cells. No difference in the electromobility of maleate NADP oxidoreductase (ME) or glucophosphate isomerase (GPI) isoenzyme in the lysates of all the cloned and uncloned cultures of E. histolytica was observed. The clones HMI-C121, HMI-C131, HMI-G143 and HMI-C144 had three bands of hexokinase (HK) while all uncloned cultures and one of clones, HMI-C145 had only two bands. Though cloned and uncloned cultures had a single PGM band, the relative electromobility (rf) of phosphoglucomutase (PGM) for clone HMI-C131, HMI-C143 HMI-C144 was relatively less (rf 0.075) and these were also significantly (P less than 0.001) less cytotoxic to BHK cells as compared to clone HMI-C121. It is felt that axenic E. histolytica culture consists of several populations (clones) and expression of isoenzymes pattern or cytotoxic potentials would depend upon the population which predominantly multiples and outgrows other populations in the culture system.

Characterization of a monoclonal antibody that selectively recognizes a subset of Entamoeba histolytica isolates

Monoclonal antibody 2D7.10 recognized an antigen present in seven of nine isolates of axenically cultured Entamoeba histolytica and absent in all other Entamoeba isolates studied. The antigen was absent in two isolates: 200:NIH and Rahman. All nine isolates belonged to pathogenic zymodeme II. Western blot (immunoblot) analysis and treatment with periodate and the proteolytic enzyme trypsin suggest that the antigen recognized by 2D7.10 is a carbohydrate moiety.

Characterization of an immuno-dominant variable surface antigen from pathogenic and nonpathogenic Entamoeba histolytica

A 125-kD surface antigen of Entamoeba histolytica is recognized by 73% of immune sera from patients with amoebic liver abscesses. Using pooled human immune sera a cDNA clone (lambda cM17) encoding this antigen (M17) has been isolated from a lambda gt11 expression library of the virulent stain E. histolytica HM1:IMSS. Monospecific antibodies, purified by binding to phage lysate of lambda cM17, and mAb FA7 reacted exclusively with the 125-kD antigen by Western blot analysis. Surface binding and cap formation are observed with patient sera, purified monospecific antiserum, and mAb FA7. Corresponding genomic clones (pBSgM17-1/2/3) were isolated by hybridization with the cDNA clone. These contained an open-reading frame of 3345 bp, which is in good agreement with the mRNA size of approximately 3.0 kb as revealed by Northern hybridization with lambda cM17. The inferred amino acid sequence predicts a 125,513 dalton protein that contains 17 potential N-linked glycosylation sites and is unusually rich in tyrosine and asparagine residues. A distinctly hydrophobic NH2-terminal region may serve as membrane anchor or signal sequence. In contrast to conservation of an immunodominant epitope recognized in pathogenic and nonpathogenic strains by monoclonal FA7 and human immune sera, amplification and sequence analysis of a 1,4000-bp fragment of this gene from a fresh nonpathogenic isolate by use of the PCR demonstrate regions of significant sequence divergence in this antigen. A 1% sequence variability among different isolates of the pathogenic strain HM1:IMSS and a 12-13% variability between pathogenic and nonpathogenic strains are revealed by comparison to published partial amino acid sequences (Tannich, E., R.D. Horstmann, J. Knobloch, and H.H. Arnold. 1989. Proc. Natl. Acad. Sci. USA. 86:5118). Some restriction enzymes were found that allowed PCR diagnosis of nonpathogenic and pathogenic isolates with the exclusion of E. histolytica-like Laredo, suggesting that a detailed study of nonpathogenic and pathogenic isolates in relation to the M17 antigen sequence will provide a basis of differentiating isolates.

Serum antibodies to Giardia lamblia by age in populations in Colorado and Thailand

We measured levels of antibodies to Giardia lamblia by age in serum specimens from persons in Denver, Colorado, and Soongnern, Thailand. Serum levels of immunoglobulin (Ig) G, IgM, and IgA G lamblia-specific antibodies measured by enzyme-linked immunosorbent assay increased substantially during childhood in both geographic areas, although children in Soongnern showed significantly higher mean levels of each antibody class (P less than .05). After adolescence, levels of G lamblia-specific IgM fell steadily with age in both populations. In contrast, specific IgA levels remained elevated throughout life among the Thai but decreased to low levels among adults in Denver. Similarly, rates of carriage of G lamblia were high among children aged 1 to 4 years in Denver and Soongnern (14.3% versus 26.5%, respectively) but were much lower among adults in Denver (0% versus 14%; P less than .01). These data suggest that levels of G lamblia-specific IgM may reflect exposure to the parasite early in life in both areas. Levels of parasite-specific IgA may reflect recurrent exposure to G lamblia in Soongnern, where G lamblia is endemic, but less frequent exposure to the parasite in Denver, where exposure is often episodic.

Current hypotheses on synergistic microbial gangrene

We have reviewed spreading infections of the dermis, with special reference to the importance of synergy in their causation. Evidence for this is accumulating from both clinical studies and from studies in laboratory animals. Necrotizing fasciitis (rapid spread over 24 h) can be caused by beta-haemolytic streptococci, sometimes with Staphylococcus aureus, or by mixed infections of aerobes and anaerobes, often of gut origin. Animal studies provide good evidence that S. aureus can potentiate the beta-haemolytic streptococcal infection in necrotizing fasciitis. There is also evidence that mixtures of aerobes and anaerobes can act synergistically, but animal models for necrotizing fasciitis have not been developed. Anaerobic cellulitis (variable rate of spread from hours to days) can be caused by mixed aerobes and anaerobes or by mixed clostridia. Animal studies provide good evidence for synergy in the former. Meleney's synergistic postoperative gangrene (slow spread over weeks) may be cutaneous amoebiasis: the animal model of Brewer and Meleney relates to the more rapid infections of anaerobic cellulitis.