Detection of Dientamoeba fragilis by culture

Dientamoeba fragilis associated with microbiome diversity changes in acute gastroenteritis patients

This study examined the correlation between intestinal protozoans and the bacterial microbiome in faecal samples collected from 463 patients in New Zealand who were diagnosed with gastroenteritis. In comparison to traditional microscopic diagnosis methods, Multiplexed-tandem PCR proved to be more effective in detecting intestinal parasites. Among the identified protozoans, Blastocystis sp. and Dientamoeba fragilis were the most prevalent. Notably, D. fragilis was significantly associated with an increase in the alpha-diversity of host prokaryotic microbes. Although the exact role of Blastocystis sp. and D. fragilis as the primary cause of gastroenteritis remains debatable, our data indicates a substantial correlation between these protozoans and the prokaryote microbiome of their hosts, particularly when compared to other protists or patients with gastroenteritis but no detectable parasitic cause. These findings underscore the significance of comprehending the contributions of intestinal protozoans, specifically D. fragilis, to the development of gastroenteritis and their potential implications for disease management.

Identification of a Cyclospora cayetanensis Oocyst Antigens and Their Validity in the Detection of Immunogenic Patterns of Cyclosporiasis Patients

INTRODUCTION

The diagnosis of cyclosporiasis is currently based on the microscopic detection of oocysts, which may provide invalid results. The availability of simple, objective immunological screening tests would facilitate epidemiological studies of cyclosporiasis. Therefore, the present study aimed to identify the antigens of Cyclospora cayetanensis oocysts and their validity in serodiagnosis.

METHODS

According to parasitological and molecular diagnoses, three study groups were specified. Group (G) I included 30 patients with cyclosporiasis, GII included 12 patients with other parasitic infections, and GIII included 16 healthy subjects. SDS-PAGE was used to analyse C. cayetanensis antigens, and the validity of western blotting and enzyme-linked immunosorbent assays (ELISAs) was then assessed amongst the sera of all study groups.

RESULTS

The C. cayetanensis antigenic profile showed eight characteristic bands with molecular weights ranging from 14 to 175 kDa. Western blot analysis of sera revealed 93.3% (28/30 of GI) and 92.8% (26/28 of GII and III) sensitivity and specificity, respectively, dividing the patients in GI into four subgroups. The most frequent diagnostic bands (71.4% of GI sera) showed weights of 26-28 kDa, followed by 71 kDa (53.6%). ELISA sensitivity was 90% (27/30), and specificity was 78.6%. Validation showed perfect agreement between the PCR and western blot results, and ELISA presented substantial agreement with both the PCR and western blot results.

CONCLUSIONS

Our findings suggest the existence of high immunogenic diversity in C. cayetanensis and indicate that the 26-28 kDa immunogenic groups may potentially be used as a diagnostic marker of cyclosporiasis. Due to the high validity of ELISA, it might be the test of choice for the routine serodiagnosis of cyclosporiasis.

Two-day enema antibiotic therapy for parasite eradication and resolution of symptoms

BACKGROUND

Blastocystis hominis (B. hominis) and Dientamoeba fragilis (D. fragilis) are two protozoan parasites of human bowel that are found throughout the world. There is still debate about the pathogenicity of these protozoans, despite them being commonly associated with gastrointestinal symptoms and can cause health issue in both children and adults. These parasites are usually transmitted through faecal-oral contact particularly under poor hygiene conditions or food/water contamination. Once a person is infected, the parasites live in the large intestine and are passed in the faeces.

AIM

To investigate the effect of triple antibiotic therapy using enema infusion in the treatment of B. hominis and D. fragilis infections.

METHODS

This retrospective longitudinal study was conducted in a single medical centre, which included fifty-four patients (≥ 18 years) who were positive for D. fragilis, B. hominis or both between 2017 and 2018. The treatment consisted of triple antibiotics that were infused over two consecutive days through rectal enema. Faecal samples were collected from participants pre- and post-treatment and were tested for parasites using microscopy and polymerase chain reaction. Patients’ symptoms were recorded prior and after the treatment as well as patient demographic data.

RESULTS

Patients (n = 54), were either positive for B. hominis (37%), D. fragilis (35%) or both (28%). All patients completed the two-day treatment and no serious adverse effect was reported. The most common side effect experienced by the patients during the treatment was urine discolouration which was cleared by six weeks of follow-up. Common symptoms reported prior to treatment were diarrhoea, abdominal pain, constipation and fatigue. Other symptoms included abdominal discomfort, dizziness and blood in the stool. Eighty-nine percent of patients completed a final stool test post-treatment. At six weeks post-treatment, 79% of patients cleared the parasites from their faeces. Symptoms such as abdominal discomfort, dizziness and blood in the stool decreased significantly at both seven days and six weeks post-treatment (P < 0.040). The enema retention time, bowel preparation, previous antibiotic treatment or previous gastrointestinal problems had no significant effect on parasite eradication.

CONCLUSION

Overall, eradication of parasites and improvement of clinical outcomes were observed in treated patients, showing the efficacy of this combination to eradicate the parasites and provide positive clinical outcome.

MALDI-TOF MS as a new tool for the identification of Dientamoeba fragilis

BACKGROUND

In this study for the first time, a Dientamoeba fragilis protein profile by MALDI-TOF MS was created in order to identify specific markers for the application of this technology in the laboratory diagnosis of dientamoebiasis. In particular, one D. fragilis reference strain was used to create a reference spectrum and 14 clinical isolates to verify the reliability of the obtained results.

RESULTS

While 15 peaks were found to be discriminating between the reference strain and the culture medium used, six peaks, observed in all the 14 strains tested, were considered as markers able to identify D. fragilis.

CONCLUSIONS

In our hands, MALDI-TOF MS technology was demonstrated as a useful tool to be used in association with or in replacement of the real-time PCR assay for the identification of D. fragilis used in our laboratory on xenic cultures, due to its accuracy, rapidity and low cost.

A Mexican Honeymoon Marred by Gastrointestinal Upset: A Case of Dientamoeba fragilis Causing Post-infectious Irritable Bowel Syndrome

Dientamoeba fragilis (D. fragilis) is an anaerobic intestinal protozoan parasite that has been associated with irritable bowel syndrome (IBS)-like symptoms. We report a case of post-infectious IBS caused by D. fragilis treated successfully with metronidazole.

A 33-year-old African American male with an unremarkable past medical history was seen in the office with a three-month history of intermittent, generalized, crampy abdominal pain with bloating and flatulence without associated weight loss. He visited Mexico for his honeymoon four months ago. Initial lab work was normal. Dietary changes including fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAP) diet and loperamide were prescribed with the presumptive diagnosis of IBS; however, his symptoms persisted. Three samples of stool for ova and parasites (O&P) were positive for D. fragilis. The patient was treated with metronidazole for 14 days. Repeat fecal O&P were negative. Upon follow-up, the patient’ symptoms substantially improved with a resolution of abdominal pain and flatulence.

Infection caused by D. fragilis may be symptomatic or asymptomatic. It is transmitted by the fecal-oral route. Symptoms include abdominal pain, bloating, and alteration of bowel movements, resembling IBS. The diagnosis is made via the detection of D. fragilis trophozoites in appropriately fixed and stained stool samples or by a polymerase chain reaction. Treatment options include tetracyclines, paromomycin, metronidazole, and Iodoquinol. Further epidemiologic studies may help in elucidating the association between D. fragilis and IBS.

Repertory of eukaryotes (eukaryome) in the human gastrointestinal tract: taxonomy and detection methods

Eukaryotes are an important component of the human gut, and their relationship with the human host varies from parasitic to commensal. Understanding the diversity of human intestinal eukaryotes has important significance for human health. In the past few decades, most of the multitudes of techniques that are involved in the diagnosis of the eukaryotic population in the human intestinal tract were confined to pathological and parasitological aspects that mainly rely on traditionally based methods. However, development of culture-independent molecular techniques comprised of direct DNA extraction from faeces followed by sequencing, offer new opportunities to estimate the occurrence of eukaryotes in the human gut by providing data on the entire eukaryotic community, particularly not-yet-cultured or fastidious organisms. Further broad surveys of the eukaryotic communities in the gut based on high throughput tools such as next generation sequencing might lead to uncovering the real diversity of these ubiquitous organisms in the human intestinal tract and discovering the unrecognized roles of these eukaryotes in modulating the host immune system and inducing changes in host gut physiology and ecosystem.

Dientamoeba fragilis, the Neglected Trichomonad of the Human Bowel

Dientamoeba fragilis is a protozoan parasite of the human bowel, commonly reported throughout the world in association with gastrointestinal symptoms. Despite its initial discovery over 100 years ago, arguably, we know less about this peculiar organism than any other pathogenic or potentially pathogenic protozoan that infects humans. The details of its life cycle and mode of transmission are not completely known, and its potential as a human pathogen is debated within the scientific community. Recently, several major advances have been made with respect to this organism's life cycle and molecular biology. While many questions remain unanswered, these and other recent advances have given rise to some intriguing new leads, which will pave the way for future research. This review encompasses a large body of knowledge generated on various aspects of D. fragilis over the last century, together with an update on the most recent developments. This includes an update on the latest diagnostic techniques and treatments, the clinical aspects of dientamoebiasis, the development of an animal model, the description of a D. fragilis cyst stage, and the sequencing of the first D. fragilis transcriptome.

Wide genetic variations at 18S ribosomal RNA locus of Cyclospora cayetanensis isolated from Egyptian patients using high resolution melting curve

A variable clinical picture of cyclosporiasis including gastrointestinal tract (GIT) symptomatic or asymptomatic beside extraintestinal consequences suggests a possibility of heterogenicity of Cyclospora cayetanensis. The present work aimed to explore the possibility of genetic variation of C. cayetanensis using high-resolution melting (HRM) curve of polymerase chain reaction (PCR) amplified 18S rRNA genes. DNAs extracted from the stool samples of 70 cyclosporiasis patients were amplified and scanned by PCR/HRM curve. The results showed that there are four different genotypic profiles of C. cayetanensis with presence of mixed ones. Although Tm of all profiles was within the same range, they were discerned by plotting of the temperature-shifted florescence difference between normalized melting curves (dF/dT). Genotypic profile I was found alone in 40 % of patients and mixed with genotypic profile II and/or III in 25.7 % of patients, followed by genotypic profile II in 14.3 % then genotypic profile III and IV (10 % each). A significant relation was found between genotypic profiles and GIT symptomatic status as profile I and profile II were mostly detected in patients with acute GIT symptoms without or with chronic illness, respectively, while profile IV cases only were GIT asymptomatic. Statistical significance relations between genotypic profiles and age, gender, residence and oocyst shape index were determined. In conclusion, PCR/HRM proved a wide variation on C. cayetanensis genes that could be reflected on its pathogenic effects and explaining the variability of the clinical manifestations presented by cyclosporiasis patients.

A microscopic description and ultrastructural characterisation of Dientamoeba fragilis: an emerging cause of human enteric disease

Dientamoeba fragilis is a pathogenic trichomonad found in the gastrointestinal tract of humans and is implicated as a cause of diarrhoea. Despite its discovery over a century ago, there has been no recent thorough description of this parasite by microscopy. Scanning electron microscopy, transmission electron microscopy, confocal and light microscopy were therefore used to characterise D. fragilis populations growing in xenic culture. Two different populations - smooth and ruffled cells - were identifiable by scanning electron microscopy. No flagella, pelta structures, undulating membrane or pseudocyst-like forms were present. The organelles in D. fragilis were analysed by transmission electron microscopy; like Trichomonas and Histomonas, D. fragilis contains hydrogenosomes that presumably represent the site of anaerobic respiration. The nuclear morphology of D. fragilis trophozoites grown in vitro and trophozoites from clinical isolates were also compared by confocal microscopy and light microscopy. The majority of cells grown in culture were mononucleate while most cells in permanent stained faecal smears were binucleate. The two nuclei of D. fragilis are morphologically indistinguishable and contain equivalent amounts of DNA as determined by DAPI staining. The approximate cell and nuclear volume of four isolates of D. fragilis were measured and shown to be comparable to other trichomonads. In addition, the discovery of a virus-like particle is reported, to our knowledge for the first time in D. fragilis. This study therefore provides extensive and novel details of the ultrastructure of a neglected protozoan parasite that is an emerging cause of human disease.

Newly defined conditions for the in vitro cultivation and cryopreservation of Dientamoeba fragilis: new techniques set to fast track molecular studies on this organism

Dientamoeba fragilis is a pathogen of the human gastrointestinal tract that is a common cause of diarrhoea. A paucity of knowledge on the in vitro cultivation and cryopreservation of Dientamoeba has meant that few studies have been conducted to investigate its biology. The objective of this study was to define, for the first time, in vitro culture conditions able to support the long-term in vitro growth of Dientamoeba. Also, we aimed to define a suitable method for cryopreserving viable Dientamoeba trophozoites. A modified BD medium, TYGM-9, Loeffler's slope medium, Robinson's medium, Medium 199, Trichosel and a Tritrichomonas fetus medium were compared, using cell counts, for their ability to support the growth of D. fragilis at various temperatures and atmospheric conditions. Loeffler's slope medium supported significantly better growth compared to other media. A temperature of 42°C and a microaerophilic atmosphere were also optimum for Dientamoeba growth. To our knowledge, this is the first study to describe and compare different culture media and conditions for the growth of clinical isolates of D. fragilis. This new technology will aid the development of diagnostics for dientamoebiasis as well as facilitate large-scale sequencing projects that will fast track molecular studies on D. fragilis.

Blastocystis hominis and Dientamoeba fragilis in patients fulfilling irritable bowel syndrome criteria

Studies have suggested a possible role for Blastocystis hominis and Dientamoeba fragilis in the etiology of irritable bowel syndrome (IBS). We studied the prevalence of B. hominis and D. fragilis in patients with IBS-diarrhea (IBS-D). Three hundred and thirty patients were enrolled, 171 (52%) with IBS-D and 159 (48%) were controls, respectively. Stool microscopy, culture, and polymerase chain reaction (PCR) for B. hominis and D. fragilis were done. B. hominis was positive by stool microscopy in 49% (83/171) of IBS compared to 24% (27/159) in control (p < 0.001). B. hominis culture was positive in 53% (90/171) in IBS compared to 16% (25/159) in control (p < 0.001). B. hominis PCR was positive in 44% (75/171) in IBS compared to 21% (33/159) in control (p < 0.001). D. fragilis microscopy was positive in 3.5% (6/171) in IBS-D compared to 0.6% (1/159) in control (p = 0.123). D. fragilis culture was positive in 4% (7/171) in IBS compared to 1.3% (2/159) in control (p = 0.176). D. fragilis PCR was positive in 4% (6/171) in IBS-D compared to 0% (0/159) in control (p = 0.030). B. hominis is common, while D. fragilis was less prevalent in our patients with IBS-D. B. hominis and D. fragilis culture had a better yield compared to stool microscopy and PCR.

Evaluation of a real-time polymerase chain reaction assay for the detection of Dientamoeba fragilis

The diagnostic value of a real-time polymerase chain reaction (PCR) assay targeting the 5.8S rDNA of Dientamoeba fragilis was investigated as compared with conventional parasitologic methods including cultivation testing 959 fecal samples from 491 patients attending a tertiary-care hospital and suspected of having an intestinal parasitosis. The real-time PCR assay revealed 117 additional D. fragilis-positive samples as compared with conventional methods, showing 100% sensitivity and specificity in our experience. On the whole, D. fragilis infection was detected in 186 samples from 105 patients (21.4%, third in frequency among the diagnosed intestinal parasitoses). The evaluated real-time PCR assay represents an effective tool to obtain both an accurate diagnosis and a reliable epidemiologic picture of dientamoebiasis.

A review of the clinical presentation of dientamoebiasis

Among 750 symptomatic and asymptomatic patients, Dientamoeba fragilis was detected at a prevalence of 5.2% and more common than Giardia intestinalis. Most infected patients presented with diarrhea and abdominal pain with symptoms greater than 2 weeks duration being common. Bacterial and viral causes of infection were excluded by routine microbiological techniques. Treatment of D. fragilis infection with either iodoquinol, paromomycin, or combination therapy resulted in the eradication of the parasite and complete resolution of symptoms. Treatment failure/relapses were associated only with the use of metronidazole. Nineteen patients were examined for pin worm, no Enterobius vermicularis, a proposed vector of transmission, were detected. Intermittent shedding of D. fragilis was found to be highly variable. These studies confirm the pathogenic nature of D. fragilis and we recommend laboratories routinely test for the organism.

Comparison of microscopy, two xenic culture techniques, conventional and real-time PCR for the detection of Dientamoeba fragilis in clinical stool samples

Dientamoeba fragilis is a pathogenic protozoan parasite that is notoriously difficult to diagnose. The aim of this study was to determine the gold standard for laboratory detection of D. fragilis. A total of 650 human faecal samples were included in the study. All specimens underwent the following: microscopy using a permanent stain (modified iron-haematoxylin), culture using a modified Boeck and Drbohlav's medium (MBD) and TYGM-9, a conventional polymerase chain reaction (PCR) and a real-time PCR (RT-PCR). The overall prevalence of D. fragilis in the study population was 5.4% (35/650). RT-PCR detected 35 isolates, conventional PCR detected 15 isolates, MBD culture detected 14 isolates, TYGM-9 detected ten isolates, while microscopy detected 12 isolates. RT-PCR detected an additional 15 positive samples compared to the other diagnostic methods, all of which were confirmed by sequencing. When all methods were compared to each other, RT-PCR showed a sensitivity and specificity of 100 and 100%, conventional PCR 42.9 and 100%, MBD culture 40 and 100%, TYGM-9 culture 28.6 and 100%, and microscopy 34.3 and 99%, respectively. These results show that RT-PCR is the diagnostic method of choice for the detection of D. fragilis in clinical samples and, as such, should be considered as the gold standard for diagnosis.

Genetic diversity of Dientamoeba fragilis isolates of irritable bowel syndrome patients by high-resolution melting-curve (HRM) analysis

Dientamoeba fragilis is a parasite that has been recognized as a causative agent of gastrointestinal symptoms. The search for genetic variation in D. fragilis based on the small-subunit (SSU) rRNA gene using restriction fragment length polymorphism was found not useful for molecular epidemiology. In this study, genetic variability of different clinical isolates of D. fragilis was explored by high-resolution melting curve (HRM) following polymerase chain reaction (PCR) in a one-step closed-tube method. Thirty fecal samples from irritable bowel syndrome (IBS) patients having D. fragilis trophozoites and negative for other organisms were involved in this study. According to the type of diarrhea, eight patients had acute, 14 patients had chronic intermittent, and eight patients had diarrhea alternating with constipation. HRM proved that four profiles (subtypes) were present as detecting by scanning mutation. One of these profiles (profile 1) was predominant (50%). Profile 2 was present on 20%. Profiles 3 and 4 were present on 16.7% and 13.4%, respectively. No mixed profiles were detected among the samples. The melting curves characterized by T(m)1=77.17+/-0.29 degrees C in profile 1, T(m)1=77.37+/-1.45 degrees C in profile 2, T(m)1=74.24+/-0.08 degrees C and T(m)2=79.64+/-0.09 degrees C in profile 3, and T(m)1=75.51 +/- 0.09 degrees C and T(m)=79.42 +/- 0.09 degrees C in profile 4. The relation between these profiles and types of diarrhea proved that the majority of patients having profile 1 (73.4%) and profile 4 (75%) had chronic intermittent diarrhea. All of the patients having profile 2 had acute diarrhea while all of the patients having profile 3 had diarrhea alternating with constipation. Although profile 1 was detected among all types of diarrhea, it was corresponding to 11/14 of patients with chronic intermittent diarrhea. All the differences were clinically and statistically significant. In conclusion, HRM following PCR was proved as a wide variation on D. fragilis genotypes that could be related to the characters of diarrhea among IBS patients. As the differences in HRM reflect different sequences of SSU RNA gene, thus, another study for identifying the sequences of these isolates (profiles) will be done and published later.

Dientamoeba fragilis in swine population: A preliminary investigation

Dientamoeba fragilis, a protozoan with worldwide distribution is considered to be responsible for enteric disease in humans. A wide spectrum of clinical symptoms including; diarrhoea (acute or prolonged), flatulence, abdominal pains and other unspecific bowel symptoms have been ascribed to this parasite. Asymptomatic infection has also been reported. Dientamoeba fragilis is as its name indicates an extremely delicate protozoon and only the trophozoite has ever been demonstrated in stool samples. The definitive diagnosis of this infection is based on demonstration in permanently stained stool samples. In Italy examination of ova and parasite (O&P) samples are not currently performed. This protozoan is extremely difficult to cultivate but molecular techniques such as the Polymerase Chain Reaction offer promise as a means of diagnosing infection. The epidemiology of Dientamoebiasis is not clear. This paper will present preliminary results from a study looking for the parasite's presence in swine faeces. The possible role of pigs as a reservoir of infection was studied; 121 faecal samples from breeding and fattening pigs were examined using a Giemsa permanent stain. Dientamoeba fragilis was found in 53 (43.8%) of the stool samples examined.

Irritable bowel syndrome: a review on the role of intestinal protozoa and the importance of their detection and diagnosis

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder in which abdominal pain is associated with a defect or a change in bowel habits. Gut inflammation is one of the proposed mechanisms of pathogenesis. Recent studies have described a possible role for protozoan parasites, such as Blastocystis hominis and Dientamoeba fragilis, in the etiology of IBS. Dientamoeba fragilis is known to cause IBS-like symptoms and has a propensity to cause chronic infections but its diagnosis relies on microscopy of stained smears, which many laboratories do not perform, thereby leading to the misdiagnosis of dientamoebiasis as IBS. The role of B. hominis as an etiological agent of IBS is inconclusive, due to contradictory reports and the controversial nature of B. hominis as a human pathogen. Although Entamoeba histolytica infections occur predominately in developing regions of the world, clinical diagnosis of amebiasis is often difficult because symptoms of patients with IBS may closely mimic those patients with non-dysenteric amoebic colitis. Clinical manifestations of Giardia intestinalis infection also vary from asymptomatic carriage to acute and chronic diarrhoea with abdominal pain. These IBS-like symptoms can be continuous, intermittent, sporadic or recurrent, sometimes lasting years without correct diagnosis. It is essential that all patients with IBS undergo routine parasitological investigations in order to rule out the presence of protozoan parasites as the causative agents of the clinical signs.

Dientamoebiasis: clinical importance and recent advances

Dientamoeba fragilis, an unusual single-celled parasite that was described first in 1918, is found worldwide in the gastrointestinal tract of humans. D. fragilis has emerged from obscurity recently because it is now recognized as a common cause of chronic diarrhoea and is treatable with drugs. Recent molecular studies have described D. fragilis as having two genotypes. Diagnostic tests, based on conventional and real-time PCR, have been developed that will provide a rapid, sensitive and specific diagnosis of D. fragilis. These tests will also aid the elucidation of the host distribution and the life cycle of this pathogen.

Detection of Dientamoeba fragilis in fresh stool specimens using PCR

Dientamoeba fragilis is a trichomonad parasite that causes human gastrointestinal disease. Currently microscopy is considered to be the gold standard for diagnosis of D. fragilis infection. However, this method is time-consuming and relatively insensitive. A PCR assay based on the small-subunit ribosomal RNA gene of D. fragilis for the specific detection of D. fragilis DNA in fresh unpreserved stool samples was developed. The D. fragilis PCR was positive in 29/31 samples with positive microscopy and did not cross-react with other protozoan parasites. The PCR protocol showed a specificity of 100% and a sensitivity of 93.5% and the entire procedure can be performed in one day.

Emerging from obscurity: biological, clinical, and diagnostic aspects of Dientamoeba fragilis

Ever since its first description in 1918, Dientamoeba fragilis has struggled to gain recognition as a significant pathogen. There is little justification for this neglect, however, since there exists a growing body of case reports from numerous countries around the world that have linked this protozoal parasite to clinical manifestations such as diarrhea, abdominal pain, flatulence, and anorexia. A number of studies have even incriminated D. fragilis as a cause of irritable bowel syndrome, allergic colitis, and diarrhea in human immunodeficiency virus patients. Although D. fragilis is most commonly identified using permanently stained fecal smears, recent advances in culturing techniques are simplifying as well as improving the ability of investigators to detect this organism. However, there are limitations in the use of cultures since they cannot be performed on fecal samples that have been fixed. Significant progress has been made in the biological classification of this organism, which originally was described as an ameba. Analyses of small-subunit rRNA gene sequences have clearly demonstrated its close relationship to Histomonas, and it is now known to be a trichomonad. How the organism is transmitted remains a mystery, although there is some evidence that D. fragilis might be transmitted via the ova of the pinworm, Enterobius vermicularis. Also, it remains to be answered whether the two distinct genotypes of D. fragilis recently identified represent organisms with differing virulence.