Organization, structure, and variability of the rRNA operon of the Whipple's disease bacterium (Tropheryma whippelii)

Clinical Manifestations, Treatment, and Diagnosis of Tropheryma whipplei Infections

Whipple's disease is a rare infectious disease that can be fatal if left untreated. The disease is caused by infection with Tropheryma whipplei, a bacterium that may be more common than was initially assumed. Most patients present with nonspecific symptoms, and as routine cultivation of the bacterium is not feasible, it is difficult to diagnose this infection. On the other hand, due to the generic symptoms, infection with this bacterium is actually quite often in the differential diagnosis. The gold standard for diagnosis used to be periodic acid-Schiff (PAS) staining of duodenal biopsy specimens, but PAS staining has a poor specificity and sensitivity. The development of molecular techniques has resulted in more convenient methods for detecting T. whipplei infections, and this has greatly improved the diagnosis of this often missed infection. In addition, the molecular detection of T. whipplei has resulted in an increase in knowledge about its pathogenicity, and this review gives an overview of the new insights in epidemiology, pathogenesis, clinical manifestations, diagnosis, and treatment of Tropheryma whipplei infections.

Tropheryma whipplei as a commensal bacterium

Tropheryma whipplei is the bacterial agent of the well-known and rare Whipple's disease, mainly observed among Caucasians. This bacterium has recently been involved in other chronic and acute infections. For a long time, the only known source of the bacterium was patients with Whipple's disease; however, thanks to the advent of molecular biology, T. whipplei has now been detected in specimens from healthy individuals, mainly in stool and saliva samples. The prevalence of carriage depends on several factors, such as age, exposure and geographical area, reaching 75% in stool specimens from children less than 4 years old in rural Africa. T. whipplei is a commensal bacterium that only causes Whipple's disease in a subset of individuals, probably those with a still-uncharacterized specific immunological defect.

Prevalence of asymptomatic Tropheryma whipplei carriage among humans and nonhuman primates

BACKGROUND

The reservoir of the agent of Whipple disease is unknown. Asymptomatic carriage of Tropheryma whipplei in human stool and saliva is controversial.

METHODS

Stools and saliva specimens from 231 workers at a sewage treatment facility and from 10 patients with Whipple disease, stool specimens from 102 healthy people, and stool specimens from 127 monkeys or apes were tested for T. whipplei DNA by a quantitative real-time polymerase chain reaction with probe detection. Genotyping and culture of T. whipplei-positive samples were performed.

RESULTS

Asymptomatic carriage in stool was found in humans (ranging from a prevalence of 4% in the control group to 12% among a subgroup of sewer workers) but not in monkeys and apes. The T. whipplei load in stool was significantly lower in carriers than in patients with Whipple disease (P < .001). There was a significant prevalence gradient associated with employment responsibilities at the sewage treatment facility: workers who cleaned the underground portion of the sewers were more likely than other workers to carry T. whipplei in stool. Seven of 9 sewer workers tested positive 8 months later. Patients with Whipple disease were significantly more likely to have T. whipplei-positive saliva specimens (P = .005) and had a significantly greater T. whipplei load in saliva (P = .015), compared with asymptomatic stool carriers from the sewage facility. All non-stool carriers had T. whipplei-negative saliva specimens. T. whipplei strains were heterogeneic among sewer workers but identical within individual workers.

CONCLUSION

Chronic asymptomatic carriage of T. whipplei occurs in humans. Bacterial loads are lower in asymptomatic carriers, and the prevalence of carriage increases with exposure to sewage.

Advances in Tropheryma whipplei research: the rush to find biomarkers for Whipple's disease

Whipple's disease (WD) is a systemic chronic infection, caused by the Gram-positive bacterium Tropheryma whipplei. There are several clinical traits linked to WD: histological lesions in the GI tract in association with diverse clinical manifestations (classic WD), endocarditis with negative blood cultures, and isolated neurological infection. WD is rare, predominantly affects middle-aged men and is fatal without treatment. The most recent strategy for diagnosing WD uses the results of diastase-resistant periodic acid Schiff staining and PCR in parallel, both performed on involved organ/tissue biopsy (small intestine, cardiac valve and cerebrospinal fluid). The generation of rabbit polyclonal antibodies has enabled the detection of the bacterium in tissues by immunohistochemical staining. However, the diagnosis of WD remains an invasive procedure. The recent achievement of stable bacterial culture and sequencing of the T. whipplei genome has opened a framework for the development of a biomarker platform. Several studies in different fields have been performed, for example, transcriptomics, immunoproteomics and comparative proteomics. Biomarker candidates have been proposed for the development of less invasive procedures for diagnosing WD.

Cerebral Whipple's disease diagnosed using PCR: the first case reported from Greece

BACKGROUND

Whipple's disease (WD) is a rare multisystemic bacterial infection, with variable clinical manifestations occasionally involving the central nervous system. As the cultivation of the etiologic agent, Tropheryma whippelii, is difficult, a laboratory diagnosis is usually based on histological methods. In the last few years, molecular detection of the bacterial 16SrRNA genes by PCR, with 2 primer sets, has greatly contributed to the ability of clinicians to diagnose this disease. We present a cerebral case of WD in a 48-year-old male, successfully diagnosed using PCR with T. whippelii in the blood and feces. As far as we know this is the first case reported from Greece.

METHODS

For the diagnosis of WD, histological examination of duodenum biopsy for diastase-resistant, non-acid fast, periodic acid Schiff (PAS)-positive inclusions in macrophages, and molecular detection of the 16SrRNA genes of T. whippelii by PCR in cerebrospinal fluid, blood, and feces, were performed.

RESULTS

The histological detection was negative. PCR results were positive in the blood and feces of the patient and negative in the cerebrospinal fluid. Seven months after the onset of antimicrobial therapy, PCR was negative in all three clinical specimens.

CONCLUSIONS

The application of PCR proved to be an invaluable tool for the recognition, differential diagnosis and early initiation of antimicrobial therapy for the patient diagnosed with WD, a disease which is generally fatal if it remains untreated.

Whipple disease

Whipple disease is a rare disease caused by infection with the bacterium Tropheryma whippelii. Humans are the only known host for the infection. The signs of systemic infection include gastrointestinal problems, weight loss, and arthritis. Signs of central nervous system infection include cognitive changes, supranuclear gaze palsy, altered level of consciousness, and movement disorders. The diagnosis is based on clinical findings as well as microscopic examination of biopsy specimens and, more recently, polymerase chain reaction (PCR) analysis, which has high sensitivity and specificity. Although the organism historically has been difficult to culture, several recent attempts have been successful. Antibiotic treatment is recommended for 1 year while monitoring the clinical signs and cerebrospinal fluid PCR results.

Culture of Tropheryma whipplei from human samples: a 3-year experience (1999 to 2002)

The culture of Tropheryma whipplei, the bacterium responsible for Whipple's disease, has been established only recently. Our objective is to describe, based on our experience, the culture of T. whipplei in HEL cells detected by immunofluorescence staining. Over 3 years, we received 18 samples for T. whipplei culture from 15 patients with Whipple's disease. Ten duodenal biopsy specimens from 10 patients with digestive symptoms were available. Five cardiac valves and three blood samples from five patients with endocarditis were also available. We correlated the results of culture with the type of sample and the culture procedure. Seven isolates were obtained, and three were subsequently established for more than 4 passages. The mean delay for the primary detection was 30 days. The bacterium was isolated more frequently from sterile specimens (5 of 8) than from duodenal biopsy specimens (2 of 10), but the difference (P = 0.14) was not significant. Decontamination of digestive samples containing colistin, amphotericin B, and cephalotin or ciprofloxacin did not impair the isolation of T. whipplei. The use of vancomycin precludes the primary isolation (7 of 12 versus 0 of 6; P = 0.08) and the establishment of T. whipplei (3 of 12 versus 0 of 6; P = 0.5). Omitting samples cultured with vancomycin, the establishment of the strain was significantly higher when antibiotics were prescribed for no more than 7 days (3 of 4 versus 0 of 8; P = 0.03). Our results demonstrate that samples must be collected within 1 week of an antibiotic regimen's initiation for the successful establishment of the bacterium.

Tropheryma whipplei Twist: a human pathogenic Actinobacteria with a reduced genome

The human pathogen Tropheryma whipplei is the only known reduced genome species (<1 Mb) within the Actinobacteria [high G+C Gram-positive bacteria]. We present the sequence of the 927303-bp circular genome of T. whipplei Twist strain, encoding 808 predicted protein-coding genes. Specific genome features include deficiencies in amino acid metabolisms, the lack of clear thioredoxin and thioredoxin reductase homologs, and a mutation in DNA gyrase predicting a resistance to quinolone antibiotics. Moreover, the alignment of the two available T. whipplei genome sequences (Twist vs. TW08/27) revealed a large chromosomal inversion the extremities of which are located within two paralogous genes. These genes belong to a large cell-surface protein family defined by the presence of a common repeat highly conserved at the nucleotide level. The repeats appear to trigger frequent genome rearrangements in T. whipplei, potentially resulting in the expression of different subsets of cell surface proteins. This might represent a new mechanism for evading host defenses. The T. whipplei genome sequence was also compared to other reduced bacterial genomes to examine the generality of previously detected features. The analysis of the genome sequence of this previously largely unknown human pathogen is now guiding the development of molecular diagnostic tools and more convenient culture conditions.

Analysis of conserved non-rRNA genes of Tropheryma whipplei

The causative agent of Whipple's disease, Tropheryma whipplei, is a slow-growing bacterium that remains poorly-understood. Genetic characterization of this organism has relied heavily upon rRNA sequence analysis. Pending completion of a complete genome sequencing effort, we have characterized several conserved non-rRNA genes from T. whipplei directly from infected tissue using broad-range PCR and a genome-walking strategy. Our goals were to evaluate its phylogenetic relationships, and to find ways to expand the strain typing scheme, based on rDNA sequence comparisons. The genes coding for the ATP synthase beta subunit (atpD), elongation factor Tu (tuf), heat shock protein GroEL (groEL), beta subunit of DNA-dependent RNA polymerase (rpoB), and RNase P RNA (rnpB) were analyzed, as well as the regions upstream and downstream of the rRNA operon. Phylogenetic analyses with all non-rRNA marker molecules consistently placed T. whipplei within the class, Actinobacteria. The arrangement of genes in the atpD and rpoB chromosomal regions was also consistent with other actinomycete genomes. Tandem sequence repeats were found upstream and downstream of the rRNA operon, and downstream of the groEL gene. These chromosomal sites and the 16S-23S rRNA intergenic spacer regions were examined in the specimens of 11 patients, and a unique combination of tandem repeat numbers and spacer polymorphisms was found in each patient. These data provide the basis for a more discriminatory typing method for T. whipplei.

Detection of Tropheryma whipplei DNA in feces by PCR using a target capture method

Whipple's disease is a rare multisystemic bacterial infection with variable clinical manifestations. For decades, the laboratory diagnosis was based on the demonstration of periodic acid Schiff-positive inclusions in macrophages of gastrointestinal biopsies. PCR has improved the diagnosis of Whipple's disease due to its increased sensitivity compared to histopathological analysis. To avoid invasive procedures for taking specimens, we have investigated the possibility of detecting Tropheryma whipplei DNA in feces rather than in biopsies or gastric aspirate of patients with and without Whipple's disease. Total bacterial DNA was isolated from stool specimens using Qiagen columns followed by a T. whipplei-specific hybridization step with a biotinylated capture probe and streptavidin-coated magnetic particles. The captured DNA was then amplified using the same seminested PCR targeting the 16S rRNA gene of the organism that had been applied to other specimens without capturing. For five of eight patients with Whipple's disease, duodenal biopsies and stool samples were PCR positive, whereas for the three other patients, both specimens were PCR negative. Of 84 patients without Whipple's disease, 75 tested negative in the duodenal biopsy and in the stool sample. For four, both specimens were positive. Five patients tested positive in the stool sample but not in the biopsy. However, for three of these five patients, the gastric aspirate had been PCR positive, indicating that the stool PCR result was true rather than false positive. Compared to PCR from duodenal biopsies, stool PCR has a sensitivity of 100% and a specificity of 97.3%. Additionally, 15 PCR-positive and 22 PCR-negative stool samples were extracted using the Invisorb Spin Stool DNA kit. The simplified stool extraction showed 93.3% sensitivity and 95.5% specificity compared to the target capture method. We conclude that PCR with stool specimens with either extraction method is a sensitive and specific diagnostic tool for the detection of T. whipplei DNA and one not requiring invasive sampling procedures.

Intragenomic and intraspecific polymorphism of the 16S-23S rDNA internally transcribed sequences of Streptomyces ambofaciens

The nucleotide composition of the internally transcribed sequences (ITSs) of the six rDNA operons of two strains of Streptomyces ambofaciens were determined. Four variable and five conserved nucleotide blocks were distinguished. Five different modular organizations were revealed for each strain and no homologous loci showed the same succession of blocks. This suggests that recombination frequently occurs between the rDNA loci, leading to the exchange of nucleotide blocks. The modular structure was also observed within the ITSs of Streptomyces coelicolor M145, which is closely related to Streptomyces ambofaciens, and Streptomyces griseus 2247, showing the same number of constant blocks but with fewer variable regions. This confirms that a high degree of ITS variability is a common characteristic among Streptomyces spp. The functional significance of the combinations of variable and constant nucleotide blocks of the ITS was examined by in silico prediction of secondary structures from nucleotide sequences. The secondary structures were shown to be analogous whatever the combination of variable/constant blocks at the intragenomic, intraspecific and interspecific levels.

Primary diagnosis of whipple disease manifesting as lymphadenopathy: use of polymerase chain reaction for detection of Tropheryma whippelii

Whipple disease is a rare, chronic multisystem disease associated with the recently characterized organism Tropheryma whippelii. Extraintestinal manifestation involving the central nervous system, heart, and joints occasionally occurs. Involvement of the abdominal lymph nodes, especially the mesenteric and periaortic nodes, is not uncommon. However, peripheral lymphadenopathy as the sole clinical manifestation of Whipple disease is rare. We describe 2 patients with Whipple disease whose initial manifestation was lymphadenopathy. Lymph nodes from both patients showed infiltration of the sinuses by macrophages containing periodic acid-Schiff-positive, diastase-resistant, sickle-like structures. Electron microscopic evaluation confirmed the presence of rod-like organisms. DNA from each sample was amplified by the polymerase chain reaction using a specific set of oligonucleotide primers developed against the 16S ribosomal RNA coding sequence of T. whippelii. The histopathologic features and differential diagnosis of lipogranulomatous lymphadenopathy secondary to Whipple disease, as well as use of molecular-based assays, are discussed.

Molecular techniques in Whipple's disease

Whipple's disease is a systemic infection, caused by the bacterium Tropheryma whipplei, with protean clinical manifestations characterized by fever, weight loss, diarrhea, polyarthritis, skin hyperpigmentation and adenopathy. For a long time, due to the inability to culture the causative organism, diagnosis was based on histologic examination of infected tissues, usually duodenal biopsies, which revealed diastase-resistant periodic acid-Schiff-positive staining. Now, PCR of various tissues or fluid is emerging as a way to diagnose Whipple's disease. However, the presence of T. whipplei DNA in saliva, gastric juice or duodenal biopsies of healthy individuals has led to questions regarding the specificity of the molecular techniques involved. After a series of failures, stable culture was achieved in 2000. Subsequently, the generation of rabbit polyclonal antibodies has led to the detection of the bacterium in tissues by immunohistology. However, culture and immunohistology are very recent techniques and are not yet widely used. Propagation of the bacterium will lead to extensive molecular knowledge of T. whipplei, which will help in the diagnosis and understanding of the epidemiology and pathogenicity of Whipple's disease.

Whipple's disease and "Tropheryma whippelii"

Whipple's disease is a rare bacterial infection that may involve any organ system in the body. It occurs primarily in Caucasian males older than 40 years. The gastrointestinal tract is the most frequently involved organ, with manifestations such as abdominal pain, malabsorption syndrome with diarrhea, and weight loss. Other signs include low-grade fever, lymphadenopathy, skin hyperpigmentation, endocarditis, pleuritis, seronegative arthritis, uveitis, spondylodiscitis, and neurological manifestations, and these signs may occur in the absence of gastrointestinal manifestations. Due to the wide variability of manifestations, clinical diagnosis is very difficult and is often made only years or even decades after the initial symptoms have appeared. Trimethoprim-sulfamethoxazole for at least 1 year is usually considered adequate to eradicate the infection. The microbiological diagnosis of this insidious disease is rendered difficult by the virtual lack of culture and serodiagnostic methods. It is usually based on the demonstration of periodic acid-Schiff-positive particles in infected tissues and/or the presence of bacteria with an unusual trilaminar cell wall ultrastructure by electron microscopy. Recently, the Whipple bacteria have been characterized at the molecular level by amplification of their 16S rRNA gene(s). Phylogenetic analysis of these sequences revealed a new bacterial species related to the actinomycete branch which was named "Tropheryma whippelli." Based on its unique 16S ribosomal DNA (rDNA) sequence, species-specific primers were selected for the detection of the organism in clinical specimens by PCR. This technique is currently used as one of the standard methods for establishing the diagnosis of Whipple's disease. Specific and broad-spectrum PCR amplifications mainly but not exclusively from extraintestinal specimens have significantly improved diagnosis, being more sensitive than histopathologic analysis. However, "T. whippelii" DNA has also been found in persons without clinical and histological evidence of Whipple's disease. It is unclear whether these patients are true asymptomatic carriers or whether differences in virulence exist among strains of "T. whippelii" that might account for the variable clinical manifestations. So far, six different "T. whippelii" subtypes have been found by analysis of their 16S-23S rDNA spacer region. Further studies of the pathogen "T. whippelii" as well as the host immune response are needed to fully understand this fascinating disease. The recent cultivation of the organisms is a promising major step in this direction.

rpoB sequence analysis of cultured Tropheryma whippelii

Until recently no isolate of Tropheryma whippelii was available, and therefore genetic studies were limited to those based on PCR amplification of conserved genes. In this study we determined the nucleotide sequence of rpoB (encoding the beta-subunit of RNA polymerase) from a cultured strain of T. whippelii using degenerate consensus PCR and genome walking. The T. whippelii rpoB consists of 3,657 bp with a 50.4% GC content and encodes 1,218 amino acids with a calculated molecular mass of 138 kDa. Comparison of T. whippelii RpoB with other eubacterial RpoB proteins indicated sequence similarity ranging from 57.19 (Mycoplasma pneumoniae) to 74.63% (Mycobacterium tuberculosis). Phylogenetic analysis of T. whippelii based on comparison of its RpoB sequence with sequences available for other bacteria was consistent with that previously derived from the 16S ribosomal DNA (rDNA) sequence, indicating that it belongs to the actinomyces clade. The sequence comparison allowed the design of a primer pair, TwrpoB.F and TwrpoB.R, specific for T. whippelii rpoB. When incorporated into a PCR, this primer pair allowed the detection of T. whippelii rpoB in three of three 16S rDNA PCR-positive biopsy specimens and zero of seven negative controls. rpoB could therefore be targeted in PCR-mediated detection and identification of this emerging bacterial species. This approach has previously been shown useful for the identification of related mycobacteria. This study underscores that a method involving isolation and then propagation of emerging bacteria is a useful way to quickly achieve extensive molecular knowledge of these pathogens.

Whipple's disease and Tropheryma whippelii: secrets slowly revealed

Whipple's disease was described in 1907 and was designated "intestinal lipodystrophy," despite the detection of bacteria in 1 specimen. This finding was later substantiated by the success of antibiotic therapy, which resulted in dramatic clinical responses, and by use of electron microscopy, which detected monomorphic bacilli in affected tissues. Many attempts at culture failed, and these bacteria were characterized as actinomycetes for the first time by means of broad-range 16S rDNA amplification and molecular phylogenetic methods. The name "Tropheryma whippelii" was proposed for this bacterium. Whipple's disease is a systemic disease that affects many organ systems, producing protean manifestations. This article summarizes recent developments with regard to this topic as well as unanswered questions regarding the pathogenesis and acquisition of infection, the biology and ecology of the organism, the clinical spectrum of disease, diagnosis of the disease, and therapy.