Salicylate increases the expression of marA and reduces in vitro biofilm formation in uropathogenic Escherichia coli by decreasing type 1 fimbriae expression

Abstract

Escherichia coli is one of the most frequent bacteria implicated in biofilm formation, which is a dynamic process whose first step consists in bacteria adhesion to surfaces through type 1 fimbriae. Salicylate induces a number of morphological and physiological alterations in bacteria including the activation of the transcriptional regulator MarA. In this report the effects of salicylate on biofilm formation and their relationship with MarA were studied. An inverse relationship was observed between in vitro biofilm formation and salicylate concentration added to the culture medium. Salicylate increases the expression of marA and decreases the expression of fimA and fimB genes in the wild-type strain. In addition, the fimA and fimB expression was decreased in a MarR mutant in which marA was also overexpressed. In conclusion, the expression of type 1 fimbriae in presence of salicylate may be regulated by the level of marA expression through fimB regulator, albeit through neither the ompX nor the tolC genes.

What does it take to stick around?

“…Paradoxically, Vila et al also report that at the time of their proteome analysis, assessment of fimS orientation in the corresponding cultures had not revealed significant phase-switch differences. 30 This apparent paradox is intriguing and could be pointing toward a transcriptional effect on fim expression that extends beyond the phase-switch. It is possible that upon downregulation of fimB in response to high salicylate, other recombinases present in this UPEC strain invert fimS ON, but fim operon transcription is impeded by the activity of a yet undefined transcriptional repressor or the inactivation of a transcriptional activator.…”

“…12,29 It is thus apparent that an intricate network of regulatory components is in place to direct and fine-tune expression of type 1 pili in response to varying environmental conditions. Augmenting this complexity is a study by Vila et al 30 published in this issue of Virulence, which describes an additional effector of type 1 pili expression and biofilm formation in UPEC.…”

“…30 Salicylate is the active ingredient in aspirin and is widely used for its anti-inflammatory effects. It is also a critical intermediate in the biosynthetic pathway that leads to the synthesis of yersiniabactin, a bacterial siderophore that is prevalent among UPEC strains.…”

“…34 In the current study, Vila et al observed an inverse relationship between biofilm formation and salicylate, such that sessility is no longer favored at high salicylate concentrations. 30 In an attempt to identify differentially expressed factors in the presence of high salicylate levels that may contribute to the observed reduction in biofilm, the authors performed proteome profiling using 2D-gel electrophoresis. 30 This approach revealed that a spot corresponding to FimA, the major pilin subunit of type 1 pili, was significantly reduced in the lysates of UPEC subjected to 1 mM of salicylate.…”

“…30 In an attempt to identify differentially expressed factors in the presence of high salicylate levels that may contribute to the observed reduction in biofilm, the authors performed proteome profiling using 2D-gel electrophoresis. 30 This approach revealed that a spot corresponding to FimA, the major pilin subunit of type 1 pili, was significantly reduced in the lysates of UPEC subjected to 1 mM of salicylate. Subsequent RT-PCR analysis verified a reduction in fimA transcript, indicating that the effect of high salicylate on type 1 pili occurs at the transcriptional level.…”