Bogan, B. species (9, 11). Type 1 fimbriae carry adhesins that recognize terminal mannose residues in the Man1-3(Man1-6)Man conformation (10). This trisaccharide is exposed on many glycoproteins, and type 1 fimbriae mediate adherence to, e.g., human small and large intestinal (3) and urinary tract (30) epithelial cells. The adherence is abolished in the presence of PhiKan 083 mannose and hence is termed mannose sensitive (MS). The role of the MS adhesin in virulence has been debated, but it may play a role in urinary tract infection (7, 18, 28). Other adhesins, including those associated with P and S fimbriae, confer mannose-resistant (MR) adherence to uroepithelial and colonic epithelial cells (3, 30, 45). MR adhesins are well-known virulence factors in urinary tract infection, septicemia, and meningitis (23, 27, 37). Furthermore, P fimbriae seem to facilitate colonization of the human bowel. Thus, strains that persist in the human intestinal microbiota (so-called resident strains) are more often P fimbriated and display MR adherence to colonic epithelial cells than strains that appear only transiently in the microbiota (4, 32, 33, 35, 43). Bacteria can switch between a fimbriated and a nonfimbriated state, a process termed phase variation (13). PhiKan 083 Phase variation of type 1 fimbriae is mediated by a 314-bp invertible DNA element (switch) which contains the promoter for (2) and whose position is regulated by two site-specific recombinases, FimB and FimE (26). Several environmental factors influence phase switch of type 1 fimbriae, including temperature and osmolarity (16, 36, 39). To maximize type 1 fimbriation, strains are usually cultured in static broth (7), in which case the hydrophobic fimbriae allow the bacteria to form a pellicle on the liquid-air interface and get full access to atmospheric oxygen. With successive passages in static broth, the proportion of fimbriated bacteria therefore increases (9, 36). The normal niche for is the bowel microbiota of humans and animals (8). The gut contents are a rich source of secretory immunoglobulin A (S-IgA), which is produced at a rate of 2 to 5 g per day in an adult human being (1). S-IgA is heavily glycosylated, and many of its carbohydrate chains terminate with mannose and act as receptors for the MS adhesin of type 1-fimbriated (44). Thus, independent of the specificity of the S-IgA, type 1-fimbriated will interact with S-IgA antibodies through a lectin-carbohydrate interaction (44). Our previous findings indicate that the lectin-carbohydrate interaction PhiKan 083 is the main mechanism for the agglutinating activity of S-IgA against type 1-fimbriated in vitro (44). About 1 individual in 600 lacks IgA in both serum and secretions but has normal levels of the other immunoglobulin isotypes (19). Approximately one-third of IgA-deficient individuals suffer from recurrent respiratory tract TM6SF1 infections (5), but most are healthy and their IgA deficiencies are discovered accidentally, e.g., PhiKan 083 at blood donor screening. We have previously shown that isolated from IgA-deficient individuals displays reduced mannose-specific adherence to colonic epithelial cells in comparison with from age-matched controls (14). Two factors contributed to this effect. First, from IgA-deficient individuals carried the operon less often than did from control individuals. Second, from IgA-deficient individuals displayed PhiKan 083 reduced mannose-specific adherence in comparison with from control individuals (14). In the present study we decided to further explore the differences in.