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Open Access Highly Accessed Research article

Molecular analysis of type 3 fimbrial genes from Escherichia coli, Klebsiella and Citrobacter species

Cheryl-lynn Y Ong1, Scott A Beatson1, Makrina Totsika1, Christiane Forestier2, Alastair G McEwan1 and Mark A Schembri1*

Author affiliations

1 Centre for Infectious Disease Research, School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane, Queensland 4072, Australia

2 Université de Clermont 1, UFR Pharmacie, Laboratoire de Bactériologie, 28 place Henri Dunant, Clermont-Ferrand, F-63001 France

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Citation and License

BMC Microbiology 2010, 10:183  doi:10.1186/1471-2180-10-183

Published: 24 June 2010

Abstract

Background

Catheter-associated urinary tract infection (CAUTI) is the most common nosocomial infection in the United States and is caused by a range of uropathogens. Biofilm formation by uropathogens that cause CAUTI is often mediated by cell surface structures such as fimbriae. In this study, we characterised the genes encoding type 3 fimbriae from CAUTI strains of Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, Citrobacter koseri and Citrobacter freundii.

Results

Phylogenetic analysis of the type 3 fimbrial genes (mrkABCD) from 39 strains revealed they clustered into five distinct clades (A-E) ranging from one to twenty-three members. The majority of sequences grouped in clade A, which was represented by the mrk gene cluster from the genome sequenced K. pneumoniae MGH78578. The E. coli and K. pneumoniae mrkABCD gene sequences clustered together in two distinct clades, supporting previous evidence for the occurrence of inter-genera lateral gene transfer. All of the strains examined caused type 3 fimbriae mediated agglutination of tannic acid treated human erythrocytes despite sequence variation in the mrkD-encoding adhesin gene. Type 3 fimbriae deletion mutants were constructed in 13 representative strains and were used to demonstrate a direct role for type 3 fimbriae in biofilm formation.

Conclusions

The expression of functional type 3 fimbriae is common to many Gram-negative pathogens that cause CAUTI and is strongly associated with biofilm growth. Our data provides additional evidence for the spread of type 3 fimbrial genes by lateral gene transfer. Further work is now required to substantiate the clade structure reported here by examining more strains as well as other bacterial genera that make type 3 fimbriae and cause CAUTI.