The mechanisms underlying the adherence of Escherichia coli O157:H7 and other enterohemorrhagic E. coli (EHEC) strains to intestinal epithelial cells are poorly understood. We have identified a chromosomal region (designated lpfABCCDE) in EHEC O157:H7 containing six putative open reading frames that was found to be closely related to the long polar (LP) fimbria operon (lpf) of Salmonella enterica serovar Typhimurium, both in gene order and in conservation of the deduced amino acid sequences. We show that lpfABCCDE is organized as an operon and that its expression is induced during the exponential growth phase. The lpf genes from EHEC strain EDL933 were introduced into a nonfimbriated (Fim ؊ ) E. coli K-12 strain, and the transformed strain produced fimbriae as visualized by electron microscopy and adhered to tissue culture cells. Anti-LpfA antiserum recognized a ca. 16-kDa LpfA protein when expressed under regulation of the T7 promoter system. The antiserum also cross-reacted with the LP fimbriae in immunogold electron microscopy and Western blot experiments. Isogenic E. coli O157:H7 lpf mutants derived from strains 86-24 and AGT300 showed slight reductions in adherence to tissue culture cells and formed fewer microcolonies compared with their wild-type parent strains. The adherence and microcolony formation phenotypes were restored when the lpf operon was introduced on a plasmid. We propose that LP fimbriae participate in the interaction of E. coli O157:H7 with eukaryotic cells by assisting in microcolony formation.Enterohemorrhagic Escherichia coli (EHEC) O157:H7 is recognized as a significant enteric pathogen that has been implicated in numerous outbreaks worldwide (reviewed in reference 24). This organism colonizes the intestine and can cause bloody or nonbloody diarrhea and hemolytic uremic syndrome. A potent cytotoxin, Shiga toxin (Stx), is the best-characterized virulence factor, but many aspects of the pathogenesis of the disease associated with E. coli O157:H7 are poorly characterized. In particular, the mechanisms underlying the adherence of EHEC to intestinal epithelial cells are not well understood (24,27). Colonization of the gastrointestinal tract, which is presumably mediated by specific adherence factors, is a key aspect of enteric infection caused by EHEC. Several potential virulence determinants of EHEC have been described, but the only adherence factor that has been demonstrated to play a role in intestinal colonization in vivo in an animal model is the outer membrane protein intimin (8,22,43). Most EHEC and all enteropathogenic E. coli (EPEC) strains produce this adhesin (17). Intimin, encoded by the eae gene, is located within the locus for enterocyte effacement (LEE) pathogenicity island, which is required for the classic attaching and effacing intestinal lesion produced by these organisms (14,15,21).The presence of a second adherence factor has been described in EPEC but not in EHEC strains. The type IV bundleforming pilus (BFP) encoded by the plasmid of EPEC strains is involved in bacteri...

SummaryThe basis for the interaction of Brucella species with the surface of epithelial cells before migration in the host within polymorphonuclear leucocytes is largely unknown. Here, we studied the ability of Brucella abortus and Brucella melitensis to adhere to cultured epithelial (HeLa and HEp-2) cells and THP-1-derived macrophages, and to bind extracellular matrix proteins (ECM). The brucellae adhered to epithelial cells forming localized bacterial microcolonies on the cell surface, and this process was inhibited significantly by pretreatment of epithelial cells with neuraminidase and sodium periodate and by preincubation of the bacteria with heparan sulphate and Nacetylneuraminic acid. Trypsinization of epithelial cells yielded increased adherence, suggesting unmasking of target sites on host cells. Notably, the brucellae also adhered to cultured THP-1 cells, and this event was greatly reduced upon removal of sialic acid residues from these cells with neuraminidase. B. abortus bound in a dose-dependent manner to immobilized fibronectin and vitronectin and, to a lesser extent, to chondroitin sulphate, collagen and laminin. In sum, our data strongly suggest that the adherence mechanism of brucellae to epithelial cells and macrophages is mediated by cellular receptors containing sialic acid and sulphated residues. The recognition of ECM (fibronectin and vitronectin) by the brucellae may represent a mechanism for spread within the host tissues. These are novel findings that offer new insights into understanding the interplay between Brucella and host cells.

Modelado de la biodegradación en biorreactores de lodos de hidrocarburos totales del petróleo intemperizados en suelos y sedimentos (Biodegradation modeling of sludge bioreactors of total petroleum hydrocarbons weathering in soil and sediments)

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