Adherent-invasive Escherichia coli isolated from Crohn's disease patients induce granulomas in vitro.

Adherent-invasive Escherichia coli (AIEC) have been shown to be highly associated with ileal Crohn's disease (CD). AIEC survive within infected macrophages, residing within the phagolysosomal compartment where they take advantage of the low pH to replicate extensively. We investigated whether, like the tuberculous bacillus which also persists within macrophages, AIEC LF82 induces the formation of granulomas, which are a common histopathological feature of CD. For this purpose, we have taken advantage of an in vitro model of human granulomas that we recently developed, based on blood-derived mononuclear cells. We demonstrated that AIEC LF82 induces aggregation of infected macrophages, fusion of some of them to form multinucleated giant cells and subsequent recruitment of lymphocytes. Light microscopy and scanning electron microscopy analysis of the cell aggregates confirmed their granuloma features. This was further confirmed by histological analysis of granuloma sections. Noteworthy, this phenomenon can be reproduced by soluble protein extracts of AIEC LF82 coated onto beads. Although the cell aggregates not completely mimic natural CD-associated granulomas, they are very similar to early stages of epithelioid granulomas.

Emended description of Rickettsia felis (Bouyer et al. 2001), a temperature-dependent cultured bacterium.

On the basis of phenotypic data obtained on the strain Marseille-URRWFXCal2(T), isolated from the cat flea Ctenocephalides felis, the description of Rickettsia felis (Bouyer et al., 2001) is emended and Marseille-URRWFXCal2(T) is proposed as the type strain of the species. On the basis of polyphasic characterization, especially the inability to grow at temperatures higher than 32 degrees C on Vero cells that allow growth of other Rickettsia to at least 35 degrees C, it is confirmed that this agent, although different from other recognized rickettsial species, is genotypically indistinguishable from bacteria previously detected within cat fleas and provisionally named ELB. Comparison of the phenotypic characteristics previously described for R. felis and those observed for the isolate in this study indicated some differences, although concurrent analysis of the two was not possible as no extant isolates of the first isolate of R. felis exist.