Mat fimbriae promote biofilm formation by meningitis-associated Escherichia coli

The mat (or ecp) fimbrial operon is ubiquitous and conserved in Escherichia coli, but its functions remain poorly described. In routine growth media newborn meningitis isolates of E coli express the meningitis-associated and temperature-regulated (Mat) fimbria, also termed E coli common plus (ECP), at 20 degrees C, and here we show that the six-gene (matABCDEF)-encoded Mat fimbria is needed for temperature-dependent biofilm formation on abiotic surfaces The matBCDEF deletion mutant of meningitis E coli IHE 3034 was defective in an early stage of biofilm development and consequently unable to establish a detectable biofilm, contrasting with IHE 3034 derivatives deleted for flagella, type 1 fimbriae or S-fimbriae, which retained the wild-type biofilm phenotype. Furthermore, induced production of Mat fimbriae from expression plasmids enabled biofilm-deficient E. coli K-12 cells to form biofilm at 20 degrees C. No biofilm was detected with IHE 3034 or MG1655 strains grown at 37 degrees C The surface expression of Mat fimbriae and the frequency of Mat-positive cells in the IHE 3034 population from 20 degrees C were high and remained unaltered during the transition from planktonic to biofilm growth and within the matured biofilm community. Considering the prevalence of the highly conserved mat locus in E coli genomes, we hypothesize that Mat fimbria-mediated biofilm formation is an ancestral characteristic of E coli