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Indole can act as an extracellular signal to regulate biofilm formation of Escherichia coli and other indole-producing bacteria

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We demonstrated previously that genetic inactivation of tryptophanase is responsible for a dramatic decrease in biofilm formation in the laboratory strain Escherichia coli S17-1. In the present study, we tested whether the biochemical inhibition of tryptophanase, with the competitive inhibitor oxindolyl-L-alanine, could affect polystyrene colonization by E. coli and other indole-producing bacteria. Oxindolyl-L-alanine inhibits, in a dose-dependent manner, indole production and biofilm formation by strain S17-1 grown in Luria–Bertani (LB) medium. Supplementation with indole at physiologically relevant concentrations restores biofilm formation by strain S17-1 in the presence of oxindolyl-L-alanine and by mutant strain E. coli 3714 (S17-1 tnaA::Tn5) in LB medium. Oxindolyl-L-alanine also inhibits the adherence of S17-1 cells to polystyrene for a 3-h incubation time, but mutant strain 3714 cells are unaffected. At 0.5 mg/mL, oxindolyl-L-alanine exhibits inhibitory activity against biofilm formation in LB medium and in synthetic urine for several clinical isolates of E. coli, Klebsiella oxytoca, Citrobacter koseri, Providencia stuartii, and Morganella morganii but has no affect on indole-negative Klebsiella pneumoniae strains. In conclusion, these data suggest that indole, produced by the action of tryptophanase, is involved in polystyrene colonization by several indole-producing bacterial species. Indole may act as a signalling molecule to regulate the expression of adhesion and biofilm-promoting factors.Key words: Escherichia coli, biofilm, indole, tryptophanase, signalling molecule.

Nous avions précédemment montré que l'inactivation génétique de la tryptophanase était responsable d'une très forte diminution de la capacité à former un biofilm pour la souche de laboratoire Escherichia coli S17-1. Cette nouvelle étude a été réalisée dans le but de déterminer les effets d'une inactivation biochimique de la tryptophanase par l'inhibiteur compétitif oxindolyl-L-alanine sur la formation de biofilm de souches bactériennes de E. coli et d'autres espèces productrices d'indole. L'oxindolyl-L-alanine inhibite la production d'indole et la formation de biofilm dans des microplaques de polystyrène de la souche S17-1 dans le milieu Luria–Bertani (LB). Une supplémentation en indole à concentrations physiologiques, restaure la formation de biofilm de la souche S17-1 en présence d'oxindolyl-L-alanine, et du mutant 3714 (S17-1 tnaA::Tn5) dans le milieu LB. L'oxindolyl-L-alanine inhibe l'adhérence au polystyrène de la souche S17-1 lors d'une incubation de 3 h sans affecter l'adhérence du mutant 3714. La formation de biofilm dans le milieu LB et dans l'urine synthétique est également inhibée en présence d'oxindolyl-L-alanine pour différentes souches cliniques de E. coli, Klebsiella oxytoca, Citrobacter koseri, Providencia stuartii et Morganella morganii mais n'est pas modifiée pour des souches de Klebsiella pneumoniae. En conclusion, la tryptophanase est impliquée dans la colonisation du polystyrène par différentes espèces bactériennes productrices d'indole. L'indole doit se comporter comme une molécule de signalisation et moduler l'expression de facteurs permettant l'adhérence bactérienne et la formation de biofilm.Mots clés : Escherichia coli, biofilm, indole, tryptophanase, molécule de signalisation.

Document Type: Research Article

Publication date: 2003-07-01

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  • Published since 1954, this monthly journal contains new research in the field of microbiology including applied microbiology and biotechnology; microbial structure and function; fungi and other eucaryotic protists; infection and immunity; microbial ecology; physiology, metabolism and enzymology; and virology, genetics, and molecular biology. It also publishes review articles and notes on an occasional basis, contributed by recognized scientists worldwide.
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