F17-like fimbriae from an invasive Escherichia coli strain producing cytotoxic necrotizing factor type 2 toxin
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K el Mazouari1, E Oswald, J P Hernalsteens
1Laboratorium Genetische Virologie, Vrije Universiteit Brussel, Belgium.
Abstract:
The F17b fimbriae encoded by the transmissible virulence plasmid Vir, also coding for cytotoxic necrotizing factor type 2, were characterized. A 5.7-kb region of Vir mediates in vitro N-acetylglucosamine-sensitive adhesion to calf intestinal villi. Sequence analysis revealed that this region codes for a structural subunit and an adhesin closely related to the F17-A and F17-G proteins encoded by the F17 fimbrial gene cluster. The F17b-A gene presents an open reading frame of 540 bp encoding a polypeptide of 180 amino acids with a putative signal peptide of 21 residues. The mature protein shows an identity of 74% with the F17-A structural subunit. This 20-kDa protein is recognized by antiserum directed against F17 fimbriae. The F17b-G gene shows an open reading frame of 1,029 bp encoding a polypeptide of 343 amino acids with a putative signal peptide of 22 residues. The F17b-G polypeptide exhibits 95% identity with the F17-G adhesin. The functional homology of the gene products was further confirmed by demonstrating that mutants in the F17-A gene can be complemented by the F17b-A gene and vice versa. These results prove that fimbriae belonging to the F17 family are also found on pathogenic Escherichia coli strains other than enterotoxigenic isolates producing heat-labile or heat-stable enterotoxin.
Insights
The F17b fimbriae, found on pathogenic Escherichia coli, mediate adhesion to calf intestines. These fimbriae are closely related to F17 fimbriae, expanding the known F17 family distribution.
Area of Science:
- Microbiology
- Molecular Biology
- Bacterial Pathogenesis
Background:
- The transmissible virulence plasmid Vir in pathogenic Escherichia coli encodes cytotoxic necrotizing factor type 2 and F17b fimbriae.
- Fimbriae are crucial for bacterial adhesion and colonization, playing a significant role in pathogenesis.
Purpose of the Study:
- To characterize the F17b fimbriae encoded by the Vir plasmid.
- To investigate the adhesive properties and genetic relationship of F17b fimbriae to other F17 fimbrial gene clusters.
Main Methods:
- Sequence analysis of a 5.7-kb region of the Vir plasmid.
- In vitro adhesion assays using calf intestinal villi.
- Gene complementation studies to assess functional homology.
Main Results:
- A 5.7-kb region of the Vir plasmid mediates N-acetylglucosamine-sensitive adhesion to calf intestinal villi.
- Sequence analysis revealed F17b-A and F17b-G genes, encoding proteins homologous to F17-A and F17-G subunits/adhesins.
- F17b-A shares 74% identity with F17-A, and F17b-G shares 95% identity with F17-G.
- Functional complementation confirmed homology between F17b-A and F17-A genes.
Conclusions:
- Fimbriae belonging to the F17 family are present on pathogenic Escherichia coli strains beyond those producing heat-labile or heat-stable enterotoxins.
- The F17b fimbriae contribute to the adhesive capabilities of pathogenic E. coli strains carrying the Vir plasmid.