Tropheryma whipplei intestinal colonization in Italian and migrant population: a retrospective observational study.

AIM: To obtain the first molecular epidemiological survey of Tropheryma whipplei intestinal colonization in Italy. Materials & methods: Retrospective, observational study to assess the prevalence of T. whipplei, the causative agent of Whipple's disease, in stool samples (real-time PCR) of patients attending the Center for Tropical Diseases (Italy) and risk factors associated. RESULTS: Overall prevalence was 6.9% (85/1240). The younger age group showed a significantly higher rate than older age group (12.7 vs 5.9%, p = 0.002). The prevalence was 4.9% for Italians and 9.3% for migrants (p = 0.003). Among the latter, children less than 10 years had higher prevalence than older ones (17.3 vs 7.3%, p = 0.003). The young age, male gender and Giardia duodenalis and Entamoeba histolytica coinfection were risk factors. CONCLUSION: Our study confirms an increased risk of acquiring T. whipplei infection during childhood, under poor sanitary conditions.

In vitro activity of pentamidine against Tropheryma whipplei.

Pentamidine is a group I intron splice inhibitor used as a chemotherapeutic agent to treat parasitic infections. It was recently found to be efficient intracellularly against Coxiella burnetii, the bacterial agent of Q fever. This in vitro activity was linked to the presence of self-splicing group I introns that disrupt the 23S rRNA of C. burnetii. However, there are several indications that pentamidine may have a wider range of antibacterial activity. The aim of this study was to determine the in vitro activity of pentamidine against Tropheryma whipplei, the agent of Whipple's disease, a chronic disease for which antibiotic treatment remains challenging. In vitro susceptibility testing of pentamidine and doxycycline was assessed both in axenic medium and in cell culture against three clinical isolates of T. whipplei using a quantitative real-time polymerase chain reaction (PCR) assay as previously described. Both doxycycline and pentamidine were found to be active against T. whipplei strains both in axenic medium and in cell culture, with minimum inhibitory concentration ranges of 0.5-1mg/L and 0.125-0.25mg/L for doxycycline and pentamidine, respectively. Pentamidine was effective in vitro against T. whipplei both intracellularly and in axenic medium. This is the first evidence of the direct efficacy of pentamidine against T. whipplei grown in axenic medium and in cells. Since pentamidine has been widely used in humans, we believe that it could be an alternative drug for the treatment of this chronic disease that should be further studied in clinical trials.

An experimental mouse model to establish Tropheryma whipplei as a diarrheal agent.

Tropheryma whipplei has long been considered as a rare bacterium causing a rare disease, Whipple's disease. However, recent advances now suggest that T. whipplei is a ubiquitous environmental bacterium that may cause gastroenteritis, commonly associated with viral pathogens. We developed an animal model to support this hypothesis. We found that orally given T. whipplei induced diarrhea in mice, without spreading into the intestines. Aggravating factors, such as damage to the intestinal mucosa, favored bacterial spreading. Indeed, bacterial presence was prolonged in stools of dextran sulfate-treated mice, and bacteria were detected in the colon. This resulted in an immune response, with T. whipplei-specific serum IgM and IgG and fecal IgA, as measured by newly introduced immuno-polymerase chain reaction technique. Our results confirm that T. whipplei is an agent causing gastroenteritis and suggest that existing mucosal damage may favor bacterial invasion of tissues.

IL-16 promotes T. whipplei replication by inhibiting phagosome conversion and modulating macrophage activation.

The replication of Tropheryma whipplei (the agent of Whipple's disease) within human macrophages is associated with the expression of IL-16, a cytokine known for its chemotactic and inflammatory properties. In this study, we asked whether IL-16 acts on T. whipplei replication by interfering with the endocytic pathway. We observed that in macrophages, T. whipplei was located within late phagosomes that were unable to fuse with lysosomes; in monocytes, T. whipplei was eliminated in phagolysosomes. Moreover, adding IL-16 to monocytes induced bacterial replication and inhibited phagolysosome formation. On the other hand, blocking IL-16 activity, either with anti-IL-16 antibodies in human macrophages or by using murine IL-16(-/-) bone marrow-derived macrophages, inhibited T. whipplei replication and rescued phagolysosome biogenesis. Furthermore, we propose that IL-16-mediated interference with the endocytic pathway is likely related to macrophage activation. First, IFNγ induced T. whipplei elimination and phagolysosome formation and inhibited IL-16 production by macrophages. Second, the full transcriptional response of murine macrophages to T. whipplei showed that T. whipplei specifically modulated the expression of 231 probes in IL-16(-/-) macrophages. Gene Ontology analysis revealed that 10 of 13 over-represented terms were linked to immune responses, including proinflammatory transcriptional factors of the NF-κB family. Our results demonstrated a previously unreported function for IL-16 in promoting bacterial replication through inhibited phagolysosome biogenesis and modulated macrophage activation program.