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Type 1 fimbriae are heteropolymeric surface organelles responsible for the D-mannose-sensitive (MS) adhesion of Escherichia coli. We recently reported that variation of receptor specificity of type 1 fimbriae can result solely from minor alterations in the structure of the gene for the FimH adhesin subunit. To further study the relationship between allelic variation of the fimH gene and adhesive properties of type 1 fimbriae, the fimH genes from five additional strains were cloned and used to complement the FimH deletion in E. coli KB18. When the parental and recombinant strains were tested for adhesion to immobilized mannan, a wide quantitative range in the ability of bacteria to adhere was noted. The differences in adhesion do not appear to be due to differences in the levels of fimbriation or relative levels of incorporation of FimH, because these parameters were similar in low-adhesion and high-adhesion strains. The nucleotide sequence for each of the fimH genes was determined. Analysis of deduced FimH sequences allowed identification of two sequence homology groups, based on the presence of Asn-70 and Ser-78 or Ser-70 and Asn-78 residues. The consensus sequences for each group conferred very low adhesion activity, and this low-adhesion phenotype predominated among a group of 43 fecal isolates. Strains isolated from a different host niche, the urinary tract, expressed type 1 fimbriae that conferred an increased level of adhesion. The results presented here strongly suggest that the quantitative variations in MS adhesion are due primarily to structural differences in the FimH adhesin. The observed differences in MS adhesion among populations of E. coli isolated from different host niches call additional attention to the possibility that phenotypic variants of FimH may play a functional role in population dynamics.Adhesion of bacteria to mucosal surfaces is thought to play an important role in both normal ecologic and pathogenic processes (4, 12). Type 1 fimbriae (9) or pili (6, 7) are the most common adhesive organelles expressed by Escherichia coli and other enterobacteria. The only known function of these structures is that they are responsible for the D-mannose-sensitive (MS) adhesion of E. coli to cells (31-34). Type 1 fimbriae are composed primarily of the structural subunit, FimA, and minor amounts of at least three ancillary subunits, FimF, FimG, and FimH (16,19,20,35). The 30-kDa FimH subunit represents the MS adhesin (2, 13-15, 17, 20, 21, 26, 30, 42, 45).We have recently shown that allelic variants of the highly conserved fimH gene (3) encode FimH subunits that confer distinct functional phenotypes (42). We proposed using the designations M, MF, and MFP phenotypes to distinguish strains that bound to yeast mannan (MN); to both MN and human plasma fibronectin (FN); or to MN, FN, and synthetic peptides, respectively (42). The present report extends our previous studies to show that FimH subunits are also capable of conferring broad quantitative differences in the ability of type 1 fimbriated strains ...

We recently reported that the type 1-fimbriated Escherichia coli strains CSH-50 and HB101(pPKIA), both K-12 derivatives, have different patterns of adhesion to yeast mannan, human plasma fibronectin, and fibronectin derivatives, suggesting functional heterogeneity of type 1 fimbriae. In this report, we provide evidence that this functional heterogeneity is due to variations in the fimH genes. We also investigated functional heterogeneity among clinical isolates and whether variation infimH genes accounts for differences in receptor specificity. Twelve isolates obtained from human urine were tested for their ability to adhere to mannan, fibronectin, periodate-treated fibronectin, and a synthetic peptide copying the 30 amino-terminal residues of fibronectin. CSH-50 and HB101(pPKLA) were tested for comparison. Selected isolates were also tested for adhesion to purified fragments spanning the entire fibronectin molecule. Three distinct functional classes, designated M, MF, and MFP, were observed. The fimH genes were amplified by PCR from chromosomal DNA obtained from representative Strains and expressed in a Afim strain (AAEC191A) transformed with a recombinant plasmid containing the entire fim gene cluster but with a translational stop-linker inserted into the fimH gene (pPKL114). Cloned fimH genes conferred on AAEC191A(pPKL114) receptor specificities mimicking those of the parent strains from which the fimH genes were obtained, demonstrating that the FimH subunits are responsible for the functional heterogeneity. RepresentativefimH genes were sequenced, and the deduced amino acid sequences were compared with the previously published FimH sequence. Allelic variants exhibiting >98% homology and encoding proteins differing by as little as a single amino acid substitution confer distinct adhesive phenotypes. This unexpected adhesive diversity within the FimH family broadens the scope of potential receptors for enterobacterial adhesion and may lead to a fundamental change in our understanding of the role(s) that type 1 fimbriae may play in enterobacterial ecology or pathogenesis.

The initial step in establishing a bacterial infection is adhesion of the organism to the epithelium of the host. Group A streptococci use multiple adhesins to attach to host cells and the types of adhesins expressed by a particular strain will determine its tissue specificity. Expression of adhesins is regulated in response to changing environmental and growth conditions. Thus, the array of adhesins expressed by a group A streptococcus will depend on the complement of its adhesin genes and on the environment. Expression of some adhesins may trigger internalization of the streptococci by host cells, which may enable the streptococci to evade antibiotics and to facilitate the penetration of deeper tissues. In this review, we present the different molecular mechanisms of adhesion utilized by group A streptococci and how these interactions lead to colonization and invasion.

SummarySerum opacity factor (SOF) is a ®bronectin-binding protein of group A streptococci that opaci®es mammalian sera and is expressed by some strains that cause impetigo, pharyngitis and acute glomerulonephritis. Although SOF is expressed by <35% of known serotypes, its role in the pathogenesis of group A streptococcal infections has not been previously investigated. The sof genes from M types 2, 28 and 49 Streptococcus pyogenes were cloned, sequenced, and their deduced amino acid sequences were compared. The gene for FnBA, a ®bronectin-binding protein from Streptococcus dysgalactiae, was also cloned and found to express an opacity factor. The leader sequences, the ®bronectin-binding domains, and the membrane anchor regions of these proteins were highly conserved. Short spans of conserved sequences were interspersed throughout the remaining parts of the proteins. The sof2 gene was insertionally inactivated in an M type 2 S. pyogenes strain, T2MR. The resultant SOF-negative mutant (YL3) did not express SOF or opacify serum, and exhibited a 71% reduction in binding ®bronectin. Complementation of the SOFnegative defect with sof28 in the recombinant strain YL3(pNZ28) fully restored ®bronectin-binding activity and the ability to opacify serum. To determine whether sof plays a role in virulence, mice were challenged intraperitoneally with these strains. None of the 10 mice infected with YL3(pNZ28) survived and only 1 out of 15 mice challenged with T2MR survived, whereas 12 out of 15 mice infected with YL3 survived. These data clearly indicate that SOF is a virulence factor, and they provide the ®rst direct evidence that a ®bro-nectin-binding protein contributes to the pathogenesis of group A streptococcal infections in vivo.