Bacterial biofilm formation is thought to enhance survival in natural environments and during interaction with hosts. A robust colonizer of the human gastrointestinal tract, Escherichia coli Nissle 1917, is widely employed in probiotic therapy. In this study, we performed a genetic screen to identify genes that are involved in Nissle biofilm formation. We found that F1C fimbriae are required for biofilm formation on an inert surface. In addition, these structures are also important for adherence to epithelial cells and persistence in infant mouse colonization. The data suggest a possible connection between Nissle biofilm formation and the survival of this commensal within the host. Further study of the requirements for robust biofilm formation may improve the therapeutic efficacy of Nissle 1917.

We demonstrate that enhanced lysozyme resistance of enteropathogenic Escherichia coli requires the plasmid-encoded regulator, Per, and is mediated by factors outside the locus for enterocyte effacement. EspC, a Per-activated serine protease autotransporter protein, conferred enhanced resistance on nonpathogenic E. coli, and a second Per-regulated, espC-independent lysozyme resistance mechanism was identified.Enteropathogenic Escherichia coli (EPEC) is an important cause of diarrhea in young children, particularly in developing countries. The locus for enterocyte effacement (LEE) pathogenicity island, present in all EPEC strains, encodes a type III secretion system (TTSS) and some TTSS effectors, as well as the intimin outer membrane protein and its translocated receptor (reviewed in reference 8). Studies have begun to elucidate the complex interactions of EPEC with host cells, particularly the LEE-mediated characteristic attaching and effacing pathophysiology (reviewed in reference 8). Typical EPEC strains, by definition, also have a large EPEC adherence factor (EAF) plasmid, which is absent in atypical EPEC. The EAF plasmid encodes type IV bundle-forming pili (Bfp), as well as a plasmid-encoded master regulator (Per) which directly or indirectly activates the transcription of LEE genes, bfp, and its own promoter (5, 25). There are other putative virulence genes on the EAF plasmid and at other locations outside the LEE, although many of these are present in only some EPEC lineages. Among them are trcA, a Rho GTPase present in EPEC2 lineage strain B171, and espC, a serine protease autotransported protein, which is encoded in a separate genomic island and is present in most EPEC1 strains, such as E2348/69 (23,26).Commensal, as well as pathogenic, E. coli have mechanisms for general and specific protection against antimicrobial peptides (1, 6), but the mechanisms by which EPEC avoid nonspecific host defenses remain largely unstudied. In this study, we evaluated EPEC resistance to C-type lysozyme, a 14.7-kDa antimicrobial peptide that is present in saliva at concentrations of about 40 g/ml, as well as on skin, in breast milk, and in tears. Lysozyme is also secreted by goblet cells into the respiratory and intestinal tracts, where it can be detected in the mucus layer. The concentration of lysozyme in stool is in the range of 4 g/ml (3). Lysozyme enzymatically cleaves ␤-1,4-glycosidic bonds between N-acetylmuramic acid and N-acetylglucosamine in peptidoglycan. Lysozyme is highly active against gram-positive organisms, and although it is less active against gram-negative bacteria, it demonstrates activity at physiological concentrations. We show that EPEC strain E2348/69 has multiple factors that confer exceptional lysozyme resistance and that these factors are outside the LEE and virulence plasmid but are under the control of Per.The MICs of E. coli strains to recombinant human lysozyme (Sigma Aldrich) were determined by broth microdilution methods advocated for testing antimicrobial peptides (24). The MIC of lysozym...