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J. Bacteriol. doi:10.1128/JB.01523-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Identification of Type 3 fimbriae in uropathogenic Escherichia coli reveals a role in biofilm formation

School of Molecular and Microbial Sciences, and Centre for Microscopy and Microanalysis, University of Queensland; Queensland Health Pathology Service, and Infection Management Services, Princess Alexandra Hospital, Brisbane, Australia

^* To whom correspondence should be addressed. Email: m.schembri{at}uq.edu.au.

	Abstract

Catheter-associated urinary tract infection (CAUTI) is the most common nosocomial infection in the United States. Uropathogenic Escherichia coli (UPEC), the most common cause of CAUTI, can form biofilms on indwelling catheters. Here, we identify and characterise novel factors that affect biofilm formation by UPEC that cause CAUTI. Sixty-five CAUTI UPEC isolates were characterised for phenotypic markers of urovirulence including agglutination and biofilm formation. One isolate, E. coli MS2027, was uniquely proficient at biofilm growth despite the absence of adhesins known to promote this phenotype. Mini-Tn5 mutagenesis of E. coli MS2027 identified several mutants with altered biofilm growth. Mutants containing insertions in genes involved in O antigen synthesis (rmlC and manB) and capsule synthesis (kpsM) possessed an enhanced biofilm phenotype. Three independent mutants deficient in biofilm growth contained an insertion in a gene locus homologous to the type 3 chaperone-usher class fimbrial genes of Klebsiella pneumoniae. The type 3 fimbrial genes (mrkABCDF), which were located on a conjugative plasmid, were cloned from E. coli MS2027 and could complement the biofilm-deficient transconjugants when reintroduced on a plasmid. Primers targeting the mrkB chaperone-encoding gene revealed its presence in CAUTI strains of Citrobacter koseri, Citrobacter freundii, Klebsiella pneumoniae and Klebsiella oxytoca. All of these mrkB-positive strains caused type 3 fimbriae-specific agglutination of tannic acid treated red blood cells. This is the first description of type 3 fimbriae in E. coli, C. koseri and C. freundii. Our data suggest that type 3 fimbriae may contribute to biofilm formation by different Gram-negative nosocomial pathogens.