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Recently we have described the molecular cloning of the genetic determinant coding for the S-fimbrial adhesin (Sfa), a sialic acid-recognizing pilus frequently found among extraintestinal Eschenchili coli isolates. Fimbriae from the resulting Sfa + E. coli K-12 clone were isolated, and an Sfa-specific antiserum was prepared. Western blots indicate that S fimbriae isolated from different uropathogenic and meningitis-associated E. coli strains, including 083:Kl isolates, were serologically related. The Sfa-specific antibodies did not cross-react with P fimbriae, but did cross-react with FlC fimbriae. Furthermore the sja+ recombinant DNAs and some cloned s/a-flanking regions were used as probes in Southem experiments. Chromosomal DNAs isolated from 018:Kl and 083:Kl meningitis strains with and without S fimbriae and from uropathogenic 06:K + strains were hybridized against these sfa-specific probes. Only one copy of the sfa determinant was identified on the chromosome of these strains. No sfa-specific sequences were observed on the chromosome of E. coli K-12 strains and an 07:Kl isolate. With the exception of small alterations in the sfa-coding region the genetic determinants for S fimbriae were identical in uropathogenic 06:K + and meningitis 018:Kl and 083:Kl strains. The sfa determinant was also detected on the chromosome of Kl isolates with an Sfa-negative phenotype, and specific cross-hybridization signals were visible after blotting against FlC-specific DNA. In addition homology among the different strains was observed in the sfa-flanking regions.
S fimbrial adbesins (Sfa), which are able to recognize sialic acid-containing receptors on eukaryotic cells, are produced by Escherichia coli strains causing urinary tract infections or newbom meningitis. We recently described tbe cloning and molecular cbaracterization of a determinant, termed sftJI, from the chromosome of an E. coli urinary tract infection strain. Herewe present data conceming a S fimbria-specific gene duster, designated sfall, of an E. coli newbom meningitis strain. Like tbe Sfal complex, Sfall consists of tbe major subunit protein SfaA (16 kDa) and the minor subunit proteins SfaG (17 kDa), SfaS (15 kDa), and SfaH (29 kDa). The genes encoding tbe subunit proteins of Sfall were identified and sequenced. Their protein sequences were calculated from the DNA sequences and compared with tbose of the Sfal complex subunits. Altbough the sequences ofthe two major SfaA subunits ditf'ered markedly, tbe sequences ofthe minor subunits sbowed only a few amino acid exchanges (SfaG, SfaH) or were completely identical (SfaS). The introduction of a site-specific mutation into the gene sfaSII and subsequent analysis of an SfaS-negative clone indicated that sfaSII codes for the sialic acid-specific adhesin of tbe meninigitis isolate. These data were confirmed by tbe isolation and characterization of tbe SfaSII protein and the determination of its N-terminal amino acid sequence. The identity between the sialic acid-specific adhesins of Sfal and Sfall revealed that difl'erences between the two Sfa complexes with respect to tbeir capacities to agglutinate erythrocytes must result from sequence alterations of subunit proteins other tban SfaS.
Binding sites in the rat brain for Escherichia coli S fimbriae associated with neontal meningitis
(1988)
Escherichia coli strains that cause sepsis and meningitis in neonatal infants carry S fimbriae that bind to sialyl galactoside units of cell surface glycoproteins. To investigate the possible role of S fimbriae in determining the tissue tropism of neonatal menlngitis, we have studied the preselice of binding sites for S fimbriae in different tissues of the neonatal rat which is susceptible to meningitis caused by S-fimbriated E. coli. Purified S fimbriae were incubated on cryostat sections of different rat oipns and their bindina was assessed by indirect immunofluorescence. In the bnin of the neonatal rat, S fimbriae specifically bound to the luminal surfaces of the vascular endothelium and of the epithelium lining the choroid plexuses and bnin ventricles. The · bindlog W.s completely inhibited by the trisaccharide NeuAca2-3Ga)ßl-4Gic, a receptor analogue of S fimbriae, and by a preceding neuraminidase treatment of the sections. A recombinant E. coli strain expressina S fimbriae adhered in large numbers to the same tissue sites in the neonatal brain sections as did the purified fimbriae, · whereas the nonfimbriated host strahi and a recombiiuuit strain expresslog P fi.mbriae did not adhere to brain tissues. The results soggest that adhesion of S-fimbriated bacteria to the binding sites observed in the neonatai bnin has a pathogenetic roJe durlog bacterial Invasion from cii'culation into the cerebrospinal fluid.
Purified S fimbriae and an Escherichia coli strain carrying the recombinant plasmid pANN801-4 that encodes S fimbriae were tested for adhesion to frozen sections of human kidney. The fimbrlae and the bacteria bound to the same tissue domains, and in both cases the binding was specifically inhibited by the receptor analog of S fimbria, sialyl(a2-3)1actose. S fimbriae bound specifically to the epithelial elements in the kidneys; to the epithelial cells of proximal and distal tubules as weil as of the collecting ducts and to the visceral and parietal glomerular epithelium. In addition, they bound to the vascular endothelium of glomerull and of the renal Interstitium. No blnding to connective tissue elements was observed. The results suggest that the biological functlon of S fimbriae is to mediate the adheslon of E. coli to human epithelial and vascular endothellal ceUs.