Differentiation of pathogenic from nonpathogenic Entamoeba histolytica by restriction fragment analysis of a single gene amplified in vitro

Synchronous Identification of Entamoeba histolytica, Giardia intestinalis, and Cryptosporidium spp. in Stool Samples Using a Multiplex PCR Assay

BACKGROUND

Diarrheal disease annually causes 760000 deaths in children, and 1700 million new cases are reported each year worldwide. Among the parasites, Entamoeba histolytica, Giardia intestinalis, and Cryptosporidium spp. are the most important infectious agents leading to diarrhea. Clinical presentations due to these parasites are more or less similar, and microscopy is not as much as sensitive for the detection. The aim of this study was to set up and evaluate a Multiplex PCR Assay for Synchronous Identification of Entamoeba histolytica, Giardia intestinalis, and Cryptosporidium spp. in Stool Samples.

METHODS

Samples were obtained from different sources such as culture media and patient stool samples. Primer pairs were designed using primer-BLAST, and for the extraction of DNA, the QIAamp DNA stool mini kit was used. The study was conducted in Tehran, Iran and completed in 2016.

RESULTS

The current multiplex PCR assay for the detection of E. histolytica achieved sensitivity and specificity of 86.36% (95% CI: 65.09% to 97.09) and 95.74 % (95% CI: 85.46% to 99.48%), respectively. Sensitivity and specificity of the test for G. intestinalis was 90.91% (95% CI: 70.84% to 98.88%) and 95.74% (95%CI: 85.46% to 99.48%), respectively, and for the detection of Cryptosporidium, multiplex PCR showed a sensitivity of 90.91% (95% CI: 70.84% to 98.88%) and specificity of 95.74% (95%CI: 85.46% to 99.48%).

CONCLUSION

Multiplex PCR in this study showed admissible sensitivity and specificity for the detection of E. histolytica, G. intestinalis, and Cryptosporidium spp. in fecal samples.

Application of Multiplex PCR for Detection and Differentiation of Entamoeba histolytica, Entamoeba dispar and Entamoeba moshkovskii

BACKGROUND

Entamoeba moshkovskii and E. dispar are impossible to differentiate microscopically from the pathogenic species E. histolytica. Multiplex polymerase chain reaction (Multiplex PCR) is a widespread molecular biology technique for amplification of multiple targets in a single PCR experiment.

METHODS

For detection and differentiation of the three-microscopy indistinguishable Entamoeba species in human, multiplex PCR assay using different DNA extraction methods was studied. A conserved forward primer was derived from the middle of the small-subunit rRNA gene, and reverse primers were designed from signature sequences specific to each of these three Entamoeba species.

RESULTS

A 166-bp PCR product with E. histolytica DNA, a 580-bp product with E. moshkovskii DNA and a 752-bp product with E. dispar DNA were generated in a single-round and multiplex PCR reaction.

CONCLUSION

We recommend this PCR assay as an accurate, rapid, and effective diagnostic method for the detection and discrimination of these three Entamoeba species in both routine diagnosis of amoebiasis and epidemiological surveys.

Evaluation of antigen detection and polymerase chain reaction for diagnosis of amoebic liver abscess in patients on anti-amoebic treatment

BACKGROUND

Diagnosis of amoebic liver abscess (ALA) in patients on anti-amoebic drugs is difficult. There is scanty data on this issue using Entamoeba histolytica (E. histolytica) lectin antigen and polymerase chain reaction (PCR). We studied utility of lectin antigen, PCR, and IgG antibody in diagnosis of liver abscess in patients on anti-amoebic treatment. Liver aspirate of 200 patients, of which 170 had anti-amoebic drug prior to drainage, was tested for E. histolytica lectin antigen by (ELISA), PCR, bacterial culture, and serum IgG antibody by (ELISA). Classification of abscesses was based on result of anti-amoebic IgG antibody and bacterial culture, E. histolytica PCR and bacterial culture, and E. histolytica lectin antigen and bacterial culture.

FINDINGS

Using anti-amoebic IgG antibody and bacterial culture, 136/200 (68.0%) were classified as ALA, 12/200 (6.0%) as pyogenic liver abscess (PLA), 29/200 (14.5%) as mixed infection, and 23/200 (11.5%) remained unclassified. Using amoebic PCR and bacterial culture 151/200 (75.5%) were classified as ALA, 25/200 (12.5%) as PLA, 16/200 (8.0%) as mixed infection, and 8/200 (4.0%) remained unclassified. With E. histolytica lectin antigen and bacterial culture, 22/200 (11.0%) patients were classified as ALA, 39/200 (19.5%) as PLA, 2/200 (1.0%) as mixed infection, and 137/200 (68.5%) remained unclassified.

CONCLUSIONS

E. histolytica lectin antigen was not suitable for classification of ALA patients who had prior anti-amoebic treatment. However, PCR may be used as alternative test to anti-amoebic antibody in diagnosis of ALA.

PCR diagnosis of Entamoeba histolytica cysts in stool samples

Amebiasis is a protozoan disease caused by Entamoeba histolytica and a potential health threat in areas where sanitation and hygiene are inappropriate. Highly sensitive PCR methods for detection of E. histolytica in clinical and environmental samples are extremely useful to control amebiasis and to promote public health. The present study compared several primer sets for small subunit (SSU) rDNA and histone genes of E. histolytica cysts. A 246 bp of the SSU rDNA gene of pure cysts contained in phosphate-buffered saline (PBS) and in stool samples was successfully amplified by nested PCR, using the 1,147-246 bp primer set, of the primary PCR products which were pre-amplified using the 1,147 bp primer as the template. The detection limit of the nested PCR using the 1,147-246 primer set was 10 cysts in both groups (PBS and stool samples). The PCR to detect histone gene showed negative results. We propose that the nested PCR technique to detect SSU rDNA can be used as a highly sensitive genetic method to detect E. histolytica cysts in stool samples.

Evaluation of a Single PCR Assays on Cp5 Gene for Differentiation of Entamoeba histolytica and E. dispar

BACKGROUND

We examined a molecular method with a single-PCR for amplification of a part of CP5 gene enabling us to differentiate the pathogenic species, Entamoeba histolytica, from the non-pathogenic species, E. dispar.

METHODS

We developed a single PCR method for this purpose. After investigation of GenBank, primer pairs were designed from highly conserved regions of cysteine proteinase (CP5) gene. The primers were utilized in PCR using isolated genomic DNA template of E. histolytica and the PCR products were then sequenced. The same primer and method for PCR was used for isolated genomic DNA template of E. dispar.

RESULTS

A fragment of about 950 bp was isolated in PCR by using DNA from E. histolytica, however, no banding pattern was produced by using the same primers for E. dispar. We characterized CP5 gene at molecular level in E. histolytica isolates from 22 positive; including 20 non-dysentery samples isolated from both cities as well as two dysentery samples isolated only from Tabriz. Nucleotide sequence comparison in gene data banks (NCBI, NIH) revealed significant homology with CP5 gene in E. histolytica isolates

CONCLUSION

We developed a PCR method, which could detect simply and rapidly E. histolytica by amplifying a specific PCR fragment.

Rapid Diagnosis of Intestinal Parasitic Protozoa, with a Focus on Entamoeba histolytica

Entamoeba histolytica is an invasive intestinal pathogenic parasitic protozoan that causes amebiasis. It must be distinguished from Entamoeba dispar and E. moshkovskii, nonpathogenic commensal parasites of the human gut lumen that are morphologically identical to E. histolytica. Detection of specific E. histolytica antigens in stools is a fast, sensitive technique that should be considered as the method of choice. Stool real-time PCR is a highly sensitive and specific technique but its high cost make it unsuitable for use in endemic areas where there are economic constraints. Serology is an important component of the diagnosis of intestinal and especially extraintestinal amebiasis as it is a sensitive test that complements the detection of the parasite antigens or DNA. Circulating Gal/GalNac lectin antigens can be detected in the serum of patients with untreated amoebic liver abscess. On the horizon are multiplex real-time PCR assays which permit the identification of multiple enteropathogens with high sensitivity and specificity.

Molecular epidemiology of amebiasis

Entamoeba histolytica, the causative agent of human amebiasis, remains a significant cause of morbidity and mortality in developing countries and is responsible for up to 100,000 deaths worldwide each year. Entamoeba dispar, morphologically indistinguishable from E. histolytica, is more common in humans in many parts of the world. Similarly Entamoeba moshkovskii, which was long considered to be a free-living ameba, is also morphologically identical to E. histolytica and E. dispar, and is highly prevalent in some E. histolytica endemic countries. However, the only species to cause disease in humans is E. histolytica. Most old epidemiological data on E. histolytica are unusable as the techniques employed do not differentiate between the above three Entamoeba species. Molecular tools are now available not only to diagnose these species accurately but also to study intra-species genetic diversity. Recent studies suggest that only a minority of all E. histolytica infections progress to the development of clinical symptoms in the host and there exist population level differences between the E. histolytica strains isolated from the asymptomatic and symptomatic individuals. Nevertheless the underlying factors responsible for variable clinical outcome of infection by E. histolytica remain largely unknown. We anticipate that the recently completed E. histolytica genome sequence and new molecular techniques will rapidly advance our understanding of the epidemiology and pathogenicity of amebiasis.

Diagnosis of intestinal amoebiasis by using nested polymerase chain reaction-restriction fragment length polymorphism assay

BACKGROUND

Microscopy is unreliable to distinguish the pathogenic Entamoeba histolytica from the nonpathogenic Entamoeba dispar or Entamoeba moshkovskii in stool specimens.

METHODS

Nested polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) was carried out to detect E. histolytica, E. dispar, and E. moshkovskii DNA in stool samples of 202 patients positive for E. histolytica, E. dispar, or E. moshkovskii by microscopy or culture and in 35 controls. The TechLab E. histolytica II enzyme-linked immunosorbent assay (ELISA) was performed to detect Gal/GalNAc lectin in 45 stool samples positive for E. histolytica, E. dispar, or E. moshkovskii by microscopy or culture. Rapid-indirect hemagglutination assay (IHA) was performed to detect serum antiamoebic antibodies in the 85 patients positive for E. histolytica, E. dispar, or E. moshkovskii in their stool specimens and in the 35 controls.

RESULTS

Nested PCR-RFLP was positive in 175 of 202 (86.6%) patient stool samples and was negative in all 35 negative control stool samples. ELISA was positive in 29 of 45 (64.4%) patient stool samples. The IHA test was positive in 19 of 85 (22.4%) patient serum samples and in one (2.8%) of the 35 control serum samples. Nested PCR-RFLP detected E. histolytica DNA in stool specimens of 12 (63.2%) of 19 seropositive patients, and in 31 (47%) of 66 seronegative patients. TechLab E. histolytica II ELISA detected E. histolytica antigen in stool specimens of six (54.5%) of 11 seropositive patients, and in 23 (67.6%) of 34 seronegative patients.

CONCLUSIONS

Nested PCR-RFLP was useful for the specific detection of E. histolytica, E. dispar, and E. moshkovskii in stool samples.

Laboratory diagnostic techniques for Entamoeba species

The genus Entamoeba contains many species, six of which (Entamoeba histolytica, Entamoeba dispar, Entamoeba moshkovskii, Entamoeba polecki, Entamoeba coli, and Entamoeba hartmanni) reside in the human intestinal lumen. Entamoeba histolytica is the causative agent of amebiasis and is considered a leading parasitic cause of death worldwide in humans. Although recent studies highlight the recovery of E. dispar and E. moshkovskii from patients with gastrointestinal symptoms, there is still no convincing evidence of a causal link between the presence of these two species and the symptoms of the host. New approaches to the identification of E. histolytica are based on detection of E. histolytica-specific antigen and DNA in stool and other clinical samples. Several molecular diagnostic tests, including conventional and real-time PCR, have been developed for the detection and differentiation of E. histolytica, E. dispar, and E. moshkovskii in clinical samples. The purpose of this review is to discuss different methods that exist for the identification of E. histolytica, E. dispar, and E. moshkovskii which are available to the clinical diagnostic laboratory. To address the need for a specific diagnostic test for amebiasis, a substantial amount of work has been carried out over the last decade in different parts of the world. The molecular diagnostic tests are increasingly being used for both clinical and research purposes. In order to minimize undue treatment of individuals infected with other species of Entamoeba such as E. dispar and E. moshkovskii, efforts have been made for specific diagnosis of E. histolytica infection and not to treat based simply on the microscopic examination of Entamoeba species in the stool. The incorporation of many new technologies into the diagnostic laboratory will lead to a better understanding of the public health problem and measures to control the disease.

Molecular methods for diagnosis of Entamoeba histolytica in a clinical setting: an overview

The range of clinical outcomes following Entamoeba histolytica infection is likely to be influenced by the different strains of the parasite already existing in our population. There is a need for developing faster, reliable and reproducible methods for identifying the different strains of E. histolytica. This would have a major impact on the subsequent course of treatment given to patients. In the post-genomic era, different loci of the Entamoeba genome have been targeted for developing suitable probes and genetic markers. This review highlights the development made in this direction and the possibility of using these methods for routine testing of this parasite in clinical samples.

Differential detection of Entamoeba histolytica, Entamoeba dispar, and Entamoeba moshkovskii by a single-round PCR assay

A single-round PCR assay was developed for detection and differential diagnosis of the three Entamoeba species found in humans, Entamoeba moshkovskii, Entamoeba histolytica, and Entamoeba dispar, that are morphologically identical as both cysts and trophozoites. A conserved forward primer was derived from the middle of the small-subunit rRNA gene, and reverse primers were designed from signature sequences specific to each of these three Entamoeba species. PCR generates a 166-bp product with E. histolytica DNA, a 752-bp product with E. dispar DNA, and a 580-bp product with E. moshkovskii DNA. Thirty clinical specimens were examined, and the species present were successfully detected and differentiated using this assay. It was possible to detect as little as 10 pg of E. moshkovskii and E. histolytica DNA, while for E. dispar the sensitivity was about 20 pg of DNA. Testing with DNA from different pathogens, including bacteria and other protozoa, confirmed the high specificity of the assay. We propose the use of this PCR assay as an accurate, rapid, and effective diagnostic method for the detection and discrimination of these three morphologically indistinguishable Entamoeba species in both routine diagnosis of amoebiasis and epidemiological surveys.

Enhanced pro-inflammatory chemokine/cytokine response triggered by pathogenic Entamoeba histolytica : basis of invasive disease

The virulence of Entamoeba histolytica is governed by adhesion/colonization in the gut which is mediated by a galactose specific lectin. Two morphologically identical but distinct species i.e. pathogenic E. histolytica and non-pathogenic E. dispar, can be differentiated by distinct epitopes in the lectin. Both species bind to colonic epithelial cells, but only E. histolytica infection induces an inflammatory response and subsequent pathogenesis. Thus, comparing the responses of the intestinal cells to pathogenic and non-pathogenic lectins is a point of interest. The pathogenic lectin causes cytolysis of epithelial and immune-competent cells. Our data (both qualitative and mRNA quantitation) indicate that the epithelial cells responded to E. histolytica lectin with an increased expression of pro-inflammatory IL-2, IL-6, IL-8, MIP-1alpha, MCP-1, RANTES, GROalpha and GMCSF as compared to E. dispar lectin. The pathogenic LCM induced a significant increase in intracellular calcium concentration, proliferative response and chemotaxis of lymphocytes from ALA patients as compared to non-pathogenic LCM. High RANTES and IL-6 were induced in patients' lymphocytes by pathogenic LCM, along with their receptors CCR5 and CD126 as compared to NP-LCM. The local release of such a complex network of cytokines/chemokines could explain the histopathology of E. histolytica infection. The comparative low levels of these chemokines/pro-inflammatory cytokines and high levels of anti-inflammatory IL-10 in response to non-pathogenic E. dispar could explain the absence of an acute inflammatory response and the disease process. The cytokines and chemokines may provide a mechanism for initiation, amplification or containment of inflammation during disease state.

Diagnosis of amebiasis in Bangladesh

Diagnosis of amebiasis by microscopic identification of the parasite in stool and liver abscess pus is insensitive and unable to distinguish the invasive parasite E. histolytica from the commensal parasites such as E. dispar and E. moshkovskii. New approaches to the detection of E. histolytica are based on detection of E. histolytica-specific antigen and DNA in stool and other clinical samples. Several molecular diagnostic tests for diagnosis of amebiasis have been developed and used to diagnose E. histolytica in Bangladesh. We have compared the TechLab E. histolytica-specific antigen detection test with PCR assays and with isoenzyme analysis of cultured amebas. The PCR assays are based on amplification of the multi-copy small subunit ribosomal RNA gene of E. histolytica and E. dispar. PCR assays and antigen detection test had comparable sensitivities when performed directly on fresh stool specimens. The correlation of antigen detection with PCR assays for identification of E. histolytica was excellent. TechLab's E. histolytica- specific antigen detection test was both rapid and simple to perform, making it appropriate for use in the developing world, where amebiasis is most prevalent.

Identification of differentially expressed genes in virulent and nonvirulent Entamoeba species: potential implications for amebic pathogenesis

Entamoeba histolytica is a protozoan parasite that causes colitis and liver abscesses. Several Entamoeba species and strains with differing levels of virulence have been identified. E. histolytica HM-1:IMSS is a virulent strain, E. histolytica Rahman is a nonvirulent strain, and Entamoeba dispar is a nonvirulent species. We used an E. histolytica DNA microarray consisting of 2,110 genes to assess the transcriptional differences between these species/strains with the goal of identifying genes whose expression correlated with a virulence phenotype. We found 415 genes expressed at lower levels in E. dispar and 32 genes with lower expression in E. histolytica Rahman than in E. histolytica HM-1:IMSS. Overall, 29 genes had decreased expression in both the nonvirulent species/strains than the virulent E. histolytica HM-1:IMSS. Interestingly, a number of genes with potential roles in stress response and virulence had decreased expression in either one or both nonvirulent Entamoeba species/strains. These included genes encoding Fe hydrogenase (9.m00419), peroxiredoxin (176.m00112), type A flavoprotein (6.m00467), lysozyme (6.m00454), sphingomyelinase C (29.m00231), and a hypothetical protein with homology to both a Plasmodium sporozoite threonine-asparagine-rich protein (STARP) and a streptococcal hemagglutinin (238.m00054). The function of these genes in Entamoeba and their specific roles in parasite virulence need to be determined. We also found that a number of the non-long-terminal-repeat retrotransposons (EhLINEs and EhSINEs), which have been shown to modulate gene expression and genomic evolution, had lower expression in the nonvirulent species/strains than in E. histolytica HM-1:IMSS. Our results, identifying expression profiles and patterns indicative of a virulence phenotype, may be useful in characterizing the transcriptional framework of virulence.

Copper(II) complexes with substituted thiosemicarbazones of thiophene-2-carboxaldehyde: synthesis, characterization and antiamoebic activity against E. histolytica

In an effort to develop potent antiamoebic agents, a series of thiosemicarbazone (TSC) ligands 1-5 derived from thiophene-2-carboxaldehyde and N4-substituted thiosemicarbazides has been prepared and characterized using various spectroscopic techniques. Treatment of the ligands with cupric chloride produced the copper(II) complexes [Cu(TSC)2Cl2] 1a-5a where ligand bind through thionic sulfur and the azomethine nitrogen. The possible geometries of the complexes were assigned on the basis of magnetic moment, electronic and thermal patterns as well as infrared spectral studies. The thiosemicarbazones and their copper complexes were tested for their in vitro antiamoebic activity against HK-9 strain of Entamoeba histolytica and showed significant growth inhibition. The results revealed that these complexes are effective chemicals in inhibiting amoebal growth, with compound 5 (having -N(CH3)(C6H5) substituent at N4) and complexes 1a-5a being more effective than the commercial antiamoebic drug, metronidazole, based on IC50 values. These data also indicated that the compounds 3a and 5a are most effective among the complexes studied (IC50=0.26 microM of 3a and IC50=0.21 microM of 5a versus IC50=1.81 microM of metronidazole).

[Determination of Entamoeba histolytica infection in patients from Greater Metropolitan Belém, Para, Brazil, by enzyme-linked immunosorbent assay (ELISA) for antigen detection]

The epidemiological status of amebiasis has been reevaluated since Entamoeba histolytica (pathogenic) was considered a distinct species from Entamoeba dispar (non-pathogenic). We investigated E. histolytica antigens in stool samples from residents of Belém, Para State, Brazil, with commercially available enzyme-linked immunosorbent assay (E. histolytica Test, TechLab Inc., Blacksburg, USA). A total of 845 samples were analyzed, of which 248 were positive (29.35%). E. histolytica infection was more frequent in the over-14-year age group (30.36%) than in the 0-14-year group (28.28%), but the difference was not statistically significant (p < 0.05). Of all the samples, 334 were also submitted to parasitological methods (direct, Hoffman, and Faust et al.). There were discordant results between ELISA and parasitological methods in 83 samples (24.85%), with more positive results using ELISA. Our results thus suggest that intestinal amebiasis is an important public health problem in Greater Metropolitan Belém.

Real-time-PCR assay for diagnosis of Entamoeba histolytica infection

We developed a real-time-PCR assay utilizing a molecular-beacon probe for the detection of Entamoeba histolytica and compared its sensitivity to stool antigen detection and traditional PCR. A total of 205 stool and liver abscess pus specimens from patients and controls were used for this purpose, 101 (49%) of which were positive by the TechLab E. histolytica-specific antigen detection test, while the other 104 (51%) stool and liver abscess pus specimens were negative by the antigen detection test. DNA was extracted from the stool and liver abscess pus specimens by the QIAGEN method and the small-subunit rRNA gene of E. histolytica and then amplified by traditional and real-time PCR. Out of these 205 stool and liver abscess pus specimens, 124 were positive by the real-time-PCR assay and 90 were positive by the traditional-PCR test. Compared to the real-time-PCR assay, the antigen detection test was 79% sensitive and 96% specific. When the traditional-PCR test results were compared to the real-time-PCR assay, the sensitivity of traditional PCR was 72% and the specificity was 99%. In conclusion, all three methods for the detection of E. histolytica were highly specific, with real-time PCR being the most sensitive.

Comparative genomic hybridizations of Entamoeba strains reveal unique genetic fingerprints that correlate with virulence

Variable phenotypes have been identified for Entamoeba species. Entamoeba histolytica is invasive and causes colitis and liver abscesses but only in approximately 10% of infected individuals; 90% remain asymptomatically colonized. Entamoeba dispar, a closely related species, is avirulent. To determine the extent of genetic diversity among Entamoeba isolates and potential genotype-phenotype correlations, we have developed an E. histolytica genomic DNA microarray and used it to genotype strains of E. histolytica and E. dispar. On the basis of the identification of divergent genetic loci, all strains had unique genetic fingerprints. Comparison of divergent genetic regions allowed us to distinguish between E. histolytica and E. dispar, identify novel genetic regions usable for strain and species typing, and identify a number of genes restricted to virulent strains. Among the four E. histolytica strains, a strain with attenuated virulence was the most divergent and phylogenetically distinct strain, raising the intriguing possibility that genetic subtypes of E. histolytica may be partially responsible for the observed variability in clinical outcomes. This microarray-based genotyping assay can readily be applied to the study of E. histolytica clinical isolates to determine genetic diversity and potential genotypic-phenotypic associations.

Amebiasis and comparison of microscopy to ELISA technique in detection of Entamoeba histolytica and Entamoeba dispar

The analysis of records of amoebal infection in various hospitals in Kilimanjaro indicated frequent occurrence of amebiasis. The population over the age of five years had higher rate of amoebal infection compared to less than that of a five-year-old population; however, both age groups had similar patterns of amebiasis during January 1999 to June 2001. To investigate misdiagnosis of amebiasis, 226 patients (passive cases) in three hospitals and 616 individuals (active cases) from three different localities in Kilimanjaro were examined. In passive cases, the prevalences of Entamoeba histolytica and Entamoeba dispar were 1% and 7.3%, respectively. Among active cases, 1% were infected with E. histolytica, and 15% were infected with E. dispar. There were no significant differences in amoebal infection between the male and female populations. A pool of 842 stool samples was used for diagnosis of E. histolytica and E. dispar by microscopic examination or ELISA kits. The microscopic examination indicated 8.7% amoebal infection; however, using ELISA as the gold standard, the prevalence of histolytica/dispar was 0.8% and 7.4%, respectively. This study indicated that E. dispar infection was 14.5 times more prevalent than E. histolytica infection.

Distribution and differential diagnosis of Entamoeba histolytica from Entamoeba dispar by the PCR-RFLP method in Central Iran

BACKGROUND

Entamoeba histolytica and Entamoeba dispar are two morphologically indistinguishable human protozoan parasites that are genetically distinct species. The potential invasive pathogenic Entamoeba histolytica and non-invasive parasite Entamoeba dispar can be differentiated by molecular and other methods. We used polymerase chain reaction (PCR) to determine the ratio of the two species in a population in Tehran and Karaj in central Iran.

MATERIALS AND METHODS

Human stool samples (n=12 148) were randomly collected in Tehran and Karaj and examined for E. histolytica/E. dispar cysts with direct and formalin-ether methods. Eighty-seven (0.7%) cases were positive, of which 49 (62.8%) isolates were successfully cultured in Robinson s medium. A pair of oligonucleotide primers designed from sequence data for genomic DNA coding the 30-KD surface antigen of E. histolytica/E. dispar was used to amplify a 374 base-pair (bp) fragment. The electrophoretic pattern of the PCR product digested with Hinfl restriction enzyme was used for differentiation of the two species.

RESULTS

The restriction fragment length polymorphism (RFLP) pattern obtained from a standard E. histolytica isolate had two fragments (219 bp and 155 bp), but the standard isolate of E. dispar showed three fragments (155, 152 and 67 bp). Differential diagnosis of 49 isolates of E. histolytica/E. dispar from Tehran and Karaj using PCR-RFLP revealed that 46 (93.9%) were E. dispar while only 2 (4.1%) were E. histolytica. One person (2%) had a mixed infection and showed both patterns.

CONCLUSION

The differential diagnosis of the potentially pathogenic parasite E. histolytica from the non-pathogenic E. dispar is of clinical and epidemiological importance. This study demonstrated that E. dispar is much more prevalent than E. histolytica among the cyst passers in Tehran and Karaj in Central Iran.

Laboratory diagnosis of amebiasis

The detection of Entamoeba histolytica, the causative agent of amebiasis, is an important goal of the clinical microbiology laboratory. To assess the scope of E. histolytica infection, it is necessary to utilize accurate diagnostic tools. As more is discovered about the molecular and cell biology of E. histolytica, there is great potential for further understanding the pathogenesis of amebiasis. Molecular biology-based diagnosis may become the technique of choice in the future because establishment of these protozoa in culture is still not a routine clinical laboratory process. In all cases, combination of serologic tests with detection of the parasite (by antigen detection or PCR) offers the best approach to diagnosis, while PCR techniques remain impractical in many developing country settings. The detection of amebic markers in serum in patients with amebic colitis and liver abscess appears promising but is still only a research tool. On the other hand, stool antigen detection tests offer a practical, sensitive, and specific way for the clinical laboratory to detect intestinal E. histolytica. All the current tests suffer from the fact that the antigens detected are denatured by fixation of the stool specimen, limiting testing to fresh or frozen samples.

Detection and differentiation of Entamoeba histolytica and Entamoeba dispar isolates in clinical samples by PCR and enzyme-linked immunosorbent assay

Differential diagnosis of Entamoeba histolytica (pathogenic) and Entamoeba dispar (nonpathogenic), which are two morphologically identical species of amebae, is essential both for treatment decision and public health knowledge. The study reported here was designed to choose a reference differentiation technique. Stool samples (n = 95) were tested by microscopy, TechLab enzyme-linked immunosorbent assays (ELISAs), and an in-house PCR. The target for the PCR amplification was a small region (135 bp) of the SSU rRNA selected to increase the sensitivity of the test. Sixty-eight specimens tested positive by PCR: 2 for E. histolytica and 66 for E. dispar. For detection of E. dispar, ELISA performance was lower than that of microscopy in this reference context, while PCR was much more sensitive than microscopy. Given the low proportion of E. histolytica cases, test performance for this species is difficult to assess. However, for differentiation, PCR performed well on simulated samples, while ELISA gave a discordant result for one of the two samples PCR positive for E. histolytica during the study. This report also confirms that E. dispar infection is significantly higher among travelers and underlines the possibility of acquiring E. histolytica infection in regions that are not areas of endemicity. Because of its lower sensitivity, the interest of ELISA for Entamoeba detection and differentiation in stools seems questionable in nontropical regions. On the other hand, results suggest that PCR should be useful as a reference test for sensitive differentiation of both species and to contribute to physicians' decision in treatment of E. histolytica- or E. dispar-infected patients.

Real-time PCR for detection and differentiation of Entamoeba histolytica and Entamoeba dispar in fecal samples

A closed-tube, real-time PCR assay was developed for sensitive and specific detection and differentiation of the two closely related intestinal protozoan parasites Entamoeba histolytica and Entamoeba dispar directly from human feces. The assay is performed with the LightCycler system using fluorescence-labeled detection probes and primers amplifying a 310-bp fragment from the high-copy-number, ribosomal DNA-containing ameba episome. The assay was able to detect as little as 0.1 parasite per g of feces. The two pairs of primers used were specific for the respective ameba species, and results were not influenced by the presence of other Entamoeba species even when present in exceeding amounts. PCR was evaluated using several hundred stool samples from areas of amebiasis endemicity in Vietnam and South Africa, and results were compared with those of microscopy and ameba culture. PCR was found to be significantly more sensitive than microscopy or culture, as all samples positive by microscopy and 22 out of 25 (88%) samples positive by culture were also positive by PCR, but PCR revealed a considerable number of additional E. histolytica- or E. dispar-positive samples. Compared to culture and subsequent ameba differentiation by isoenzyme analysis, PCR was 100% specific for each of the two Entamoeba species. Interestingly, the comparison with PCR revealed that culture, in particular, underestimates E. histolytica infections. Given the high sensitivity and specificity of the developed PCR assay, the inability of microscopy to distinguish between the two ameba species, and the time it takes to culture and subsequently differentiate entamoebae by isoenzyme analysis, this assay is more suitable than microscopy or culture to correctly diagnose intestinal E. histolytica or E. dispar infection.

The abundant polyadenylated transcript 2 DNA sequence of the pathogenic protozoan parasite Entamoeba histolytica represents a nonautonomous non-long-terminal-repeat retrotransposon-like element which is absent in the closely related nonpathogenic species Entamoeba dispar

While comparing gene expression in the pathogenic organism Entamoeba histolytica and the closely related but nonpathogenic species Entamoeba dispar, we discovered that the E. histolytica abundant polyadenylated transcript 2 (ehapt2) and corresponding genomic copies are absent in E. dispar. Although polyadenylated, ehapt2 does not contain any overt open reading frame. Southern blot and sequence analyses revealed that about 500 copies of ehapt2 genomic elements were present in each cell and that the copies were distributed throughout the ameba genome. The various ehapt2 elements are regularly located in the vicinity of protein-encoding genes, downstream of pyrimidine-rich sequence stretches (40 to 125 bp; CT content, 79.2 to 85.5%), and are flanked by duplicated target sites of variable length. Target site duplications were obviously generated during integration of ehapt2 into the E. histolytica genome as one copy of the flanking repeat and the complete ehapt2 element are specifically absent in orthologous E. dispar genomic sequences. ehapt2 shares 3' sequences with EhRLE, a recently identified non-long-terminal-repeat (non-LTR) retrotransposon-like element of E. histolytica, which contains a conceptual open reading frame for reverse transcriptase. Thus, ehapt2 has all of the properties of nonautonomous non-LTR retrotransposons. A comparison of various E. histolytica isolates suggested that transposition of ehapt2 takes place at a very low frequency as the genomic localization of ehapt2 elements was found to be well conserved. A mobile element such as ehapt2 could be a suitable mechanism to explain the infrequent and late transition of E. histolytica from a harmless gut commensal to an invasive pathogen.

Entamoeba dispar in a terminal case of acquired immune deficiency syndrome compared with Brumpt's (1925) original cat material

A rectal biopsy from a terminal case of acquired immune deficiency syndrome is compared with a similar biopsy taken by Brumpt in 1925 from a cat which he had infected with what he named Entamoeba dispar.

Species-specific field testing of Entamoeba spp. in an area of high endemicity

Entamoeba histolytica has been separated in recent years into 2 morphologically identical species: the apathogenic E. dispar and the pathogenic E. histolytica, only the latter being pathogenic. Although various laboratory techniques allow discrimination between the 2 species there is a lack of field data about the suitability of available diagnostic tests for use in epidemiological studies and few epidemiological studies using species-specific diagnosis have been performed at community level in endemic areas, especially in sub-Saharan Africa. We conducted a repeated cross-sectional study of 967 schoolchildren in central Côte d'Ivoire to compare and evaluate light microscopy, 2 different antigen detection assays, and one polymerase chain reaction (PCR) assay. Microscopy and a non-specific antigen capture Entamoeba enzyme-linked immunosorbent assay (ELISA) were used for the primary screening of all children (time t0). The prevalence of the E. histolytica/E. dispar species complex at t0 was 18.8% by single microscopical examination and 31.4% using the non-specific ELISA. Approximately 2 months after the initial screening, fresh stool specimens were collected on 2 consecutive days (t1 and t2) from (i) all the children who were positive by microscopy at t0 (n = 182) and (ii) 155 randomly selected children who were negative at the primary screening. These samples were tested with a second antigen detection ELISA specific for E. histolytica (n = 238) and with a species-specific PCR assay (n = 193). The second and third examinations (t1 and t2) revealed an additional 43 infections with the species complex E. histolytica/E. dispar, so that the cumulative microscopical prevalence for t1 and t2 was 27.7%. The overall prevalence of E. histolytica by species-specific ELISA antigen detection was low (0.83%), while the prevalence of E. dispar was 15%. When analysing only microscopically positive samples by PCR (n = 129), the ratio E. histolytica: E. dispar was very low (1:46), suggesting that the vast majority of Entamoeba infections in this area were apathogenic. Both species-specific tests performed well but the ELISA was easier to use for large-scale field screening.

Simultaneous differentiation and typing of Entamoeba histolytica and Entamoeba dispar

Sequences corresponding to some of the polymorphic loci previously reported from Entamoeba histolytica have been detected in Entamoeba dispar. Comparison of nucleotide sequences of two loci between E. dispar strain SAW760 and E. histolytica strain HM-1:IMSS revealed significant differences in both repeat and flanking regions. The tandem repeat units varied not only in sequence but also in number and arrangement between the two species at both the loci. Using the sequences obtained, primer pairs aimed at amplifying species-specific products were designed and tested on a variety of E. histolytica and E. dispar samples. Amplification results were in complete agreement with the original species classification in all cases, and the PCR products displayed discernible size and pattern variations among the isolates.

Diagnosis of amoebic colitis by antigen capture ELISA in patients presenting with acute diarrhoea in Cairo, Egypt

We studied 84 consecutive patients presenting with acute diarrhoea (less than 1 week in duration) at an outpatient tropical medicine clinic in Cairo, Egypt. The diagnosis of amoebic colitis was established by the presence of Entamoeba histolytica galactose-inhibitable lectin antigen and the presence of occult blood in stool. Controls were 182 healthy regional people and 64 patients complaining of prolonged diarrhoea lasting more than 1 week. Entamoeba histolytica infection was found more frequently in patients with acute diarrhoea (57.1%) than in healthy controls (21.4%) or patients with prolonged diarrhoea (25%) (P < 0.001). There was a higher prevalence of Entamoeba dispar infection in the two control groups (24.2 and 20.3%, respectively, P=0.004 and 0.061) compared with those with acute diarrhoea (8.3%). Of the 84 patients with acute diarrhoea 32 had amoebic colitis (38%), and of these, 31 (97%) had at least one positive assay for serum amoebic antibodies (P < 0.001 compared with control groups). In summary, as determined by antigen-detection enzyme-linked immunosorbent assay, there is an unexpectedly high prevalence of amoebic colitis among patients presenting with acute diarrhoea to a tropical disease clinic in Cairo, Egypt.

Entamoeba histolytica and Entamoeba dispar infections as detected by monoclonal antibody in an urban slum in Fortaleza, Northeastern Brazil

In this study the authors used the Elisa-based antigen detection tests that distinguish E. histolytica from E. dispar to examine the prevalence of E. histolytica infection in individuals from an urban slum in Fortaleza, Northeastern, Brazil. This test has a sensitivity and specificity that is comparable to PCR and isoenzyme analysis, which is the gold standard. Single stools samples were obtained from 735 individuals. The prevalence of E. histolytica infection was 14.9% (110/735) and 25.4%(187/735) for E. dispar-E. histolytica complex. The most affected age group for E. histolytica /E. histolytica-E. dispar infection was the 1-5 year olds but there was no remarkable decrease with age. There was no significant difference in colonization rates between males and females. The results from this survey demonstrate that E. histolytica is highly prevalent in the Community studied. Furthermore, it offers promise for the antigen detection test as a sensitive and technically simple tool for detecting E. histolytica infection in the field.

Emerging and reemerging intestinal protozoa

The intestinal protozoa have gained importance to physicians practicing medicine in the United States, Canada, and Europe during recent years as a result of increasing world travel, the globalization of the world's economy, and the growing number of chronically immunosuppressed people. During the spring of 1996, Cyclospora cayetanensis caused diarrhea in approximately 1500 people exposed to Guatemalan raspberries. This epidemic recurred in 1997, emphasizing the risks of the global economy and food supply on which we depend. In addition to importation of intestinal protozoa from the tropics, AIDS and the increasing use of organ transplants have created a new population of people at risk for chronic infection by ubiquitous protozoa previously not known to cause serious human disease. These infections include cryptosporidiosis, isosporiasis, and microsporidiosis. Finally, Entamoeba histolytica, the etiologic agent of invasive amebiasis, has only recently been recognized to be a distinct species from a nonpathogenic but indistinguishable (by light microscopy) intestinal commensal, Entamoeba dispar. The rapidly changing epidemiology of these intestinal protozoa, as well as new approaches to diagnosis and treatment of these protozoa, are discussed.

The genome of Entamoeba histolytica

Estimation of genome size of Entamoeba histolytica by different methods has failed to give comparable values due to the inherent complexities of the organism, such as the uncertain level of ploidy, presence of multinucleated cells and a poorly demarcated cell division cycle. The genome of E. histolytica has a low G+C content (22.4%), and is composed of both linear chromosomes and a number of circular plasmid-like molecules. The rRNA genes are located exclusively on some of the circular DNAs. Karyotype analysis by pulsed field gel electrophoresis suggests the presence of 14 conserved linkage groups and an extensive size variation between homologous chromosomes from different isolates. Several repeat families have been identified, some of which have been shown to be present in all the electrophoretically separated chromosomes. The typical nucleosomal structure has not been demonstrated, though most of the histone genes have been identified. Most Entamoeba genes lack introns, have short 3' and 5' untranslated regions, and are tightly packed. Promoter analysis revealed the presence of three conserved motifs and several upstream regulatory elements. Unlike typical eukaryotes, the transcription of protein coding genes is alpha-amanitin resistant. Expressed Sequence Tag analysis has identified a group of highly abundant polyadenylated RNAs which are unlikely to be translated. The Expressed Sequence Tag approach has also helped identify several important genes which encode proteins that may be involved in different biochemical pathways, signal transduction mechanisms and organellar functions.

Amebiasis: Clinical Implications of the Recognition of Entamoeba dispar

Entamoeba histolytica was recently reclassified to recognize the existence of two genetically distinct but morphologically indistinguishable species: E. histolytica, the protozoan parasite that causes amebic dysentery and liver abscess, and Entamoeba dispar, a nonpathogenic intestinal parasite. Acceptance of this redefinition has dramatically changed both our understanding of the true epidemiology of E. histolytica and the optimal methods for diagnosing amebiasis. Molecular-based diagnostic tests using polymerase chain reaction (PCR) to amplify amebic DNA or enzyme-linked immunosorbent assay (ELISA) to identify amebic antigens in stool samples have been developed to distinguish infection with E. histolytica from infection with E. dispar. Because of its ability to differentiate strains of E. histolytica, PCR is a very useful research tool. Only the ELISA-based test is simple to perform, making it clinically useful in the developing world. To avoid unnecessary treatment of individuals infected with E. dispar, the World Health Organization has stressed the importance of making a specific diagnosis of E. histolytica infection (not E. histolytica/E. dispar) before treating for amebiasis.

A DNA sequence corresponding to the gene encoding cysteine proteinase 5 in Entamoeba histolytica is present and positionally conserved but highly degenerated in Entamoeba dispar

Cysteine proteinases of Entamoeba histolytica are considered to be one of the most important classes of molecules responsible for the parasite's ability to destroy human tissues. Interestingly, one particular cysteine proteinase, located on the surface of E. histolytica trophozoites and designated cysteine proteinase 5 (CP5), is not expressed in the closely related but nonpathogenic species Entamoeba dispar. By comparing the E. histolytica and E. dispar genomic loci containing the gene for CP5 (cp5), it was found that the position of cp5 within the genomic context is conserved between the two organisms, but that the gene is highly degenerated in E. dispar, as it contains numerous nucleotide exchanges, insertions, and deletions, resulting in multiple stop codons within the cp5 reading frame. An alignment of all available orthologous E. histolytica and E. dispar DNA sequences suggested that cp5 started to degenerate in E. dispar coincidently when the two organisms began to diverge from a common ancestor.

Application of nucleic acid amplification in clinical microbiology

The use of nucleic acid amplification methods in routine clinical microbiology laboratories is becoming increasingly widespread. The theory of polymerase chain reaction is described, including discussion of suitable microbal targets, extraction of nucleic acid from clinical samples, choice of primers, optimization of the process, laboratory design, contamination, and other problems as well as quality control. Other nucleic acid amplification methods such as ligase chain reaction, self-sustained sequence replication, strand displacement amplification, and branched DNA signal amplification are described and the choice of technology is discussed.

Does the eosinophil have a protective role in amebiasis?

While normal human eosinophils are destroyed in vitro by virulent Entamoeba histolytica, notwithstanding the presence of antibodies and complement, activated eosinophils promptly destroy the parasite although dying also at the end of the process. To study the possible in vivo participation of eosinophils in invasive amebiasis, we compared the induction of experimental amebic abscess of the liver (AAL) in gerbils (Meriones unguiculatus) previously made eosinophilic through Toxocara canis antigen injection and in normal control gerbils. After intraportal inoculation of 10(5) ameba trophozoites (6 and 24 hr), the ratio of gerbils with AAL, as well as the number and size of the microabscesses was comparable in eosinophilic and control gerbils. However, at 96 hr the number and size of the microabscesses were significantly smaller (p < 0.05) in eosinophilic gerbils. On the other hand the actuarial AAL survival curve up to 45 days post-amebic inoculation was significantly (p < 0.05) shifted to the right in controls. These results suggest that antigen-induced eosinophilia may exert a protective effect against AAL in gerbils.

Comparison of PCR, isoenzyme analysis, and antigen detection for diagnosis of Entamoeba histolytica infection

The diagnosis of amebiasis by microscopic identification of the parasite in stool is insensitive and unable to distinguish the invasive parasite Entamoeba histolytica from the commensal parasite E. dispar. In this study, we have tested a PCR technique for the detection of E. histolytica and compared it with isoenzyme analysis and the TechLab E. histolytica-specific antigen detection test. The nested-PCR test we used is based on amplification of the small subunit rRNA gene of E. histolytica and E. dispar followed by restriction digest analysis of the PCR product. Single stool samples were obtained from 98 patients from Dhaka, Bangladesh, with diarrhea: 88 patients diagnosed by microscopy and/or culture with E. histolytica and/or E. dispar infection and 10 patients without infection. Isoenzyme analysis identified 53 of the infections as E. histolytica and 28 as E. dispar. PCR and isoenzyme identification of E. histolytica agreed in 96% (51 of 53) of amebic cultures. PCR for E. histolytica was negative in all 10 samples that were negative for E. histolytica by isoenzyme and antigen detection. PCR and antigen detection had comparable sensitivities when performed directly on fresh stool specimens, identifying 87% (46 of 53) and 85% (45 of 53), respectively, of E. histolytica infections identified by isoenzyme analysis. The correlation of results by antigen detection and PCR for identification of E. histolytica in stool was 93% (45 of 48 cases). Mixed infections with E. histolytica and E. dispar were detected by PCR in 14% (12 of 88) of cases. In conclusion, all three techniques for specific identification of E. histolytica in fresh stool showed excellent correlation. Only the TechLab E. histolytica antigen detection test was both rapid and technically simple.

Molecular methods for diagnosis and epidemiological studies of parasitic infections

Direct microscopy is widely used for the diagnosis of parasitic infections although it often requires an experienced microscopist for accurate diagnosis, is labour intensive and not very sensitive. In order to overcome some of these shortcomings, molecular or nucleic acid-based diagnostic methods for parasitic infections have been developed over the past 12 years. The parasites which have been studied with these techniques include the human Plasmodia, Leishmania, the trypanosomes, Toxoplasma gondii, Entamoeba histolytica, Giardia, Trichomonas vaginalis, Cryptosporidium parvum, Taenia, Echinococcus, Brugia malayi, Wuchereria bancrofti, Loa loa and Onchocerca volvulus. Early methods, which involved hybridisation of specific probes (radiolabelled and non-radiolabelled) to target deoxyribonucleic acid (DNA), have been replaced by more sensitive polymerase chain reaction (PCR)-based assays. Other methods, such as PCR-hybridisation assays, PCR-restriction fragment length polymorphism (PCR-RFLP) assays and random amplified polymorphic DNA (RAPD) analysis have also proved valuable for epidemiological studies of parasites. The general principles and development of DNA-based methods for diagnosis and epidemiological studies will be described, with particular reference to malaria. These methods will probably not replace current methods for routine diagnosis of parasitic infections in developing countries where parasitic diseases are endemic, due to high costs. However, they will be extremely useful for genotyping parasite strains and vectors, and for accurate parasite detection in both humans and vectors during epidemiological studies.

Progress towards development of a vaccine for amebiasis

The application of molecular biologic techniques over the past decade has seen a tremendous growth in our knowledge of the biology of Entamoeba histolytica, the causative agent of amebic dysentery and amebic liver abscess. This approach has also led to the identification and structural characterization of three amebic antigens, the serine-rich Entamoeba histolytica protein (SREHP), the 170-kDa subunit of the Gal/GalNAc binding lectin, and the 29-kDa cysteine-rich protein, which all show promise as recombinant antigen-based vaccines to prevent amebiasis. In recent studies, an immunogenic dodecapeptide derived from the SREHP molecule has been genetically fused to the B subunit of cholera toxin, to create a recombinant protein capable of inducing both antiamebic and anti-cholera toxin antibodies when administered by the oral route. Continued progress in this area will bring us closer to the goal of a cost-effective oral combination "enteric pathogen" vaccine, capable of inducing protective mucosal immune responses to several clinically important enteric diseases, including amebiasis.

Preparation of a monoclonal antibody specific for Entamoeba dispar and its ability to distinguish E. dispar from E. histolytica

A monoclonal antibody (MAb), MAb ED17 (immunoglobulin G2a [IgG2a]), prepared against trophozoites of Entamoeba dispar SAW1734RclAR cultured monoxenically with Crithidia fasciculata, reacted with 25 of 26 isolates of E. dispar by an indirect fluorescent-antibody test. In contrast, the MAb failed to react with any of 20 isolates of E. histolytica or other enteric protozoan parasites. Western blot (immunoblot) analysis showed that the molecular mass of the E. dispar antigen recognized by the MAb was 160 kDa under reduced conditions. Immunoelectron microscopy revealed that the antigen was mainly located on digested C. fasciculata, but not on undigested organisms. Double staining with a mixture of MAb ED17 and MAb 4G6 (an IgG1 MAb which reacts exclusively with E. histolytica), followed by incubation with a mixture of fluorescein isothiocyanate-labeled anti-mouse IgG2a and tetramethylrhodamine isothiocyanate-labeled anti-mouse IgG1 antibodies, simultaneously identified mixed populations of E. dispar and E. histolytica. This method may prove to be useful for the accurate identification of E. dispar and E. histolytica, even in mixed infections.

Simple differential detection of Entamoeba histolytica and Entamoeba dispar in fresh stool specimens by sodium acetate-acetic acid-formalin concentration and PCR

Amoebiasis is caused by two distinct species, a pathogenic form (Entamoeba histolytica) and a nonpathogenic form (Entamoeba dispar), which are morphologically identical. Although the distinction between these two species is of great clinical importance, the methods developed for this purpose either are very time-consuming or involve laborious procedures for isolation of the DNA. We report here a simple PCR method starting with fresh stool specimen that allows for the sensitive and reliable distinction between E. histolytica and E. dispar. After initial concentration by the sodium acetate-acetic acid-formalin (SAF) method and digestion with proteinase K, a 0.88-kb sequence of the multicopy 16S rRNA gene served as a target for PCR amplification. The method starting with unpreserved specimens proved to be very sensitive and was not influenced by the quick exposure to SAF fixative during the initial concentration step. However, storage in SAF fixative prior to testing resulted in a decreased sensitivity within 2 days. The detection limit of the method was as low as one copy of the 16S rRNA gene. No cross-reactivity was observed with other common intestinal protozoa. Mixed infections involving both E. histolytica and E. dispar could easily be detected at a ratio of 1:10,000 by agarose gel electrophoresis or a DNA hybridization immunoassay.

Virulence parameters in the characterization of strains of Entamoeba histolytica

Differences in virulence of strains of Entamoeba histolytica have long been detected by various experimental assays, both in vivo and in vitro. Discrepancies in the strains characterization have been arisen when different biological assays are compared. In order to evaluate different parameters of virulence in the strains characterization, five strains of E. histolytica, kept under axenic culture, were characterized in respect to their, capability to induce hamster liver abscess, erythrophagocytosis rate and cytopathic effect upon VERO cells. It was found significant correlation between in vitro biological assays, but not between in vivo and in vitro assays. Good correlation was found between cytopathic effect and the mean number of uptaken erythrocytes, but not with percentage of phagocytic amoebae, showing that great variability can be observed in the same assay, according to the variable chosen. It was not possible to correlate isoenzyme and restriction fragment pattern with virulence indexes since all studied strains presented pathogenic patterns. The discordant results observed in different virulence assays suggests that virulence itself may not the directly assessed. What is in fact assessed are different biological characteristics or functions of the parasite more than virulence itself. These characteristics or functions may be related or not with pathogenic mechanisms occurring in the development of invasive amoebic disease.

Differentiation of Entamoeba histolytica and Entamoeba dispar in cyst-passers by immunoblot

Differentiation of invasive strains of Entamoeba histolytica according to their pathogenicity has been a topic of long debate, but now the pathogenic species only is regarded as E. histolytica while the non pathogenic species is E. dispar. The present study applied immunoblot to differentiate infections of the two species among microscopically-detected cyst-passers in Korea. The crude extract of E. histolytica separated in 5.20% gradient gels, revealed many fractions of 94, 81, 71, 50, 44, 38.5, 37.5, 29, 19, and 18 kDa when the cysteine proteinase inhibitor, E64, was supplemented. The scrum IgG antibody of 3 proven E, histolytica cases reacted with the antigenic fractions of 117, 110, 99, 68, 66, 60, 54, 52, 46, and 45 kDa. Sera of PCR confirmed 3 cases of E. dispar reacted only to the 117 kDa fraction of the E. histolytica crude extract which was regarded as non-specific. To the antigen of monoxenic E. dispar, sera of E. dispar and E. histolytica cases showed the same immunoblot reactions. The serum IgA antibody reacted with several antigenic fractions of both E. histolytica and E. dispar, but IgM and IgE antibodies showed no reaction to either antigen. Sera of 24 symptomless amebic cyst passers were screened with the E. histolytica antigen; two were found to be infected by E. histolytica and 22 were by E. dispar. The present findings suggest that in Korea most of asymptomatic cyst passers of E. histolytica are carriers of E. dispar. Immunoblot using E. histolytica antigen is a good technique for the differentiation of E. histolytica and E. dispar infections.

Isoenzyme profile as parameter to differentiate pathogenic strains of Entamoeba histolytica in Brazil

The isoenzyme profiles (IP) of 33 strains of Entamoeba histolytica isolated from patients and carriers of two regions in Brazil (Amazonia and Southeast) were determined. The enzymes phosphoglucomutase, glucose-phosphate isomerase, hexokinase and malic enzyme were considered. IP of the strains was correlated with culture conditions, time of maintenance in laboratory and clinical history of patients. The strains were maintained under polyxenic, monoxenic and axenic culture conditions: 27 polyxenic, 1 polyxenic and monoxenic, 1 polyxenic, monoxenic and axenic and 4 axenic only. The patients were symptomatic and asymptomatic. The symptomatic patients presented either non dysenteric (NDC) or dysenteric colitis (DC), associated or not with hepatic abscess (HA). One patient presented anal amoeboma (AM). The analysis of IP for isolates maintained in polyxenic culture showed non pathogenic IP (I) for strains from carriers and patients with NDC, while the strains isolated from patients presenting DC, HA and AM resulted in isolates II or XIX pathogenic IP. This parameter was not able to differentiate strains from carriers from symptomatic patients when these strains were found in axenic or monoxenic culture. All these strains displayed pathogenic IP (II), demonstrating the inability of this parameter to classifying for virulence since it showed identical IP for strains isolated from carriers or symptomatic patients.

Putative serine/threonine protein kinase expressed in complement-resistant forms of Entamoeba histolytica

Entamoeba histolytica is susceptible to complement attack in its lumen-dwelling state and develops complement resistance during pathogenic tissue invasion. As experimental evidence suggests that this change in phenotype is accompanied by a change in gene expression, we constructed a subtractive cDNA library to identify genes involved. Poly(A) + RNA from complement-sensitive trophozoites was subtracted from single stranded cDNA derived from complement-resistant ones. Transcripts enriched in the library were found to code for a putative polypeptide comprising all sequence elements characteristic for serine/threonine protein kinases. The gene contains an intron of 46 nucleotides and two polyadenylation sites. Northern-blot analyses confirmed that the gene is expressed in both tissue-derived and laboratory-grown forms of complement-resistant E. histolytica.

Protozoa. Amebiasis

The intestinal protozoan parasite Entamoeba histolytica causes amebic dysentery and amebic liver abscess, and ranks third worldwide among parasitic causes of death. The application of molecular techniques to the study of this organism have led to major advances in understanding the pathophysiology of amebic infection. This article reviews what is currently known about the pathogenesis, clinical manifestations, diagnosis, and treatment of amebiasis.

Direct sequencing of the PCR amplified SSU rRNA gene of Entamoeba dispar and the design of primers for rapid differentiation from Entamoeba histolytica

Since 1993, strains of Entamoeba histolytica sensu lato have been assigned to 2 species on the basis of clinical, biochemical, immunological and genetic evidence: the pathogenic strains to E. histolytica sensu stricto, the non-pathogenic strains to Entamoeba dispar. Analysis of the gene encoding for the small subunit ribosomal RNA (SSU rDNA) supports the existence of 2 species. However, while 3 whole SSU rDNA sequences are available in the data bases for E. histolytica, only a partial sequence has been published for E. dispar. Here we report a SSU rDNA sequence for E. dispar. Compared to those of E. histolytica, this sequence shows 1.7% nucleotide substitutions. On the basis of our rDNA data, 2 primers were designed to produce polymerase chain reaction (PCR) amplification from both E. histolytica and E. dispar. Primer specificity for the 2 amoebae was assessed both theoretically against the data bases, and experimentally against a collection of eukaryotic and prokaryotic DNAs. The amplified stretch encompasses a polymorphic Dde I restriction site which allows, after cleavage of the fragment, E. histolytica and E. dispar to be distinguished. The reliability of this method of identification was assessed comparing the results with those based on classic isoenzyme analysis.

Differentiation of Korean isolates of Entamoeba histolytica from Entamoeba dispar

Cysts of Entamoeba histolytica are still found from humans in Korea, but not all of the cysts are known as pathogenic. The non-pathogenic strain is regarded as a different species, E. dispar. In this study, Korean isolates of conventional E. histolytica were subjected for the differentiation by polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) analysis. Human stools were screened by routine microscopic examination, and cyst or trophozoite positive stools were inoculated into Robinson media. The cultivated trophozoite positive stools were inoculated into Robinson media. The cultivated trophozoites were prepared for DNA extraction, and the DNAs were used for PCR with common primers of P1 gene. The PCR products were digested with 3 restriction enzymes and RFLP was observed. Also anti-sense primers containing the cleavage site of each restriction enzyme were designed for differentiation only by PCR. The PCR products of Korean isolates S9, S12, YS-6, and YS-27 were spliced by Taq I and Xmn I but not by Acc I, and the isolates S1, S3, S11, S15, S16, S17, S20, YS-17, and YS-44 were spliced by Acc I but not by Taq I and Xmn I. These RFLP pattern correlated well with PCR products by the species specific primers. The findings confirm that the Korean isolates S9, S12, YS-6, and YS-27 are E. histolytica and others are E. dispar. In Korea, most of the asymptomatic cyst carriers are infected by E. dispar, not by E. histolytica.