Extraintestinal pathogenic Escherichia coli (ExPEC) are a common cause of disease in both mammals and birds. A vaccine to prevent such infections would be desirable given the increasing antibiotic resistance of these bacteria. We have determined the genome sequence of ExPEC IHE3034 (ST95) isolated from a case of neonatal meningitis and compared this to available genome sequences of other ExPEC strains and a few nonpathogenic E. coli . We found 19 genomic islands present in the genome of IHE3034, which are absent in the nonpathogenic E. coli isolates. By using subtractive reverse vaccinology we identified 230 antigens present in ExPEC but absent (or present with low similarity) in nonpathogenic strains. Nine antigens were protective in a mouse challenge model. Some of them were also present in other pathogenic non-ExPEC strains, suggesting that a broadly protective E. coli vaccine may be possible. The gene encoding the most protective antigen was detected in most of the E. coli isolates, highly conserved in sequence and found to be exported by a type II secretion system which seems to be nonfunctional in nonpathogenic strains.

Curli fibers are adhesive surface fibers expressed by Escherichia coli and Salmonella enterica that bind several host extracellular matrix and contact phase proteins and were assumed to have a role in pathogenesis. The results presented here suggest that one such role is internalization into host cells. An E. coli K-12 strain transformed with a low-copy vector containing the gene cluster encoding curli fibers (csg operon) was internalized by several lines of eukaryotic cells. The internalization could be correlated with a high level of curli fiber expression and was abolished by disruption of the csg operon. The ability to be internalized by eukaryotic cells could be conferred even by the curli fiber gene cluster of a noninvasive K-12 strain, but the homologous csg cluster from a virulent septicemic E. coli isolate mediated a higher level of internalization. The finding that curli fibers promote bacterial internalization indicates a new role for curli fibers in pathogenesis.Curli fibers are thin aggregative surface fibers, connected with adhesion, which bind laminin (23), fibronectin (25), plasminogen (31), human contact phase proteins (4), and major histocompatibility complex (MHC) class I molecules (26). Curli fibers are coded for by the csg gene cluster, which is comprised of two divergently transcribed operons. One operon encodes the csgB, csgA, and csgC genes, while the other encodes csgD, csgE, csgF, and csgG. The assembly of the fibers is unique and involves extracellular self-assembly of the curlin subunit (CsgA), dependent on a specific nucleator protein (CsgB) (14). CsgD is a transcriptional activator essential for expression of the two curli fiber operons, and CsgG is an outer membrane lipoprotein involved in extracellular stabilization of CsgA and CsgB (20). The role of the other csg genes has yet to be elucidated.Curli fibers are expressed by many pathogenic isolates of Escherichia coli, as well as laboratory strains (25). Similar surface proteins were identified in both Salmonella enterica serovar Enteritidis (9) and S. enterica serovar Typhimurium (28). Curli fibers are also present in E. coli strains involved in avian colisepticemia (27)-a serious invasive disease of chickens and turkeys that is characterized by entry of the bacteria into the air sacs, bloodstream, and vital organs (36).Using PCR, we amplified the curli fiber-encoding (csg) gene cluster from a curli fiber-positive E. coli K-12 strain and cloned it in a low-copy-number vector. The resulting plasmid, when transformed to a noninvasive E. coli strain, conferred the ability to become internalized by eukaryotic cells. We have also cloned the homologous curli fiber-encoding cluster from a virulent isolate of avian E. coli O78 which could mediate a higher level of internalization. The results presented in this communication indicate that high levels of curli fiber expression can mediate entry of bacteria into eukaryotic cells and suggest that these fibers play a role in pathogenesis. MATERIALS AND METHODSBacterial strains and plasmids. T...

The aim of this study was to isolate bacteria with antimicrobial activities from the marine sponges Aplysina aerophoba and Aplysina cavernicola. The obtained 27 isolates could be subdivided into eight phylogenetically different clusters based on comparative sequence analysis of their 16S rDNA genes. The sponge isolates were affiliated with the low (Bacillus) and high G+C Gram-positive bacteria (Arthobacter, Micrococcus), as well as the alpha-Proteobacteria (unknown isolate) and gamma-Proteobacteria (Vibrio, Pseudoalteromonas). One novel Bacillus species was identified and two species were closely related to previously uncharacterized strains. Isolates with antimicrobial activity were numerically most abundant in the genera Pseudoalteromonas and the alpha-Proteobacteria. The sponge isolates show antimicrobial activities against Gram-positive and Gram-negative reference strains but not against the fungus Candida albicans. A general pattern was observed in that Gram-positive bacteria inhibited Gram-positive strains while Gram-negative bacteria inhibited Gram-negative isolates. Antimicrobial activities were also found against clinical isolates, i.e. multi-resistant Staphylococcus aureus and Staphylococcus epidermidis strains isolated from hospital patients. The high recovery of strains with antimicrobial activity suggests that marine sponges represent an ecological niche which harbors a hitherto largely uncharacterized microbial diversity and, concomitantly, a yet untapped metabolic potential.

The probiotic Escherichia coli strain Nissle 1917 (Mutaflor) of serotype O6:K5:H1 was reported to protect gnotobiotic piglets from infection with Salmonella enterica serovar Typhimurium. An important virulence property of Salmonella is invasion of host epithelial cells. Therefore, we tested for interference of E. coli strain Nissle 1917 with Salmonella invasion of INT407 cells. Simultaneous administration of E. coli strain Nissle 1917 and Salmonella resulted in up to 70% reduction of Salmonella invasion efficiency. Furthermore, invasion of Yersinia enterocolitica, Shigella flexneri, Legionella pneumophila and even of Listeria monocytogenes were inhibited by the probiotic E. coli strain Nissle 1917 without affecting the viability of the invasive bacteria. The observed inhibition of invasion was not due to the production of microcins by the Nissle 1917 strain because its isogenic microcin-negative mutant SK22D was as effective as the parent strain. Reduced invasion rates were also achieved if strain Nissle 1917 was separated from the invasive bacteria as well as from the INT407 monolayer by a membrane non-permeable for bacteria. We conclude E. coli Nissle 1917 to interfere with bacterial invasion of INT407 cells via a secreted component and not relying on direct physical contact with either the invasive bacteria or the epithelial cells.