EtcABC, a Putative EII Complex, Regulates Type 3 Fimbriae via CRP-cAMP Signaling in .

Biofilm formation by on indwelling medical devices increases the risk of infection. Both type 1 and type 3 fimbriae are important factors in biofilm formation by . We found that a putative enzyme II (EII) complex of the phosphoenolpyruvate (PEP):carbohydrate phosphotransferase system (PTS), (EIIA)- (EIIB)- (EIIC), regulated biofilm and type 3 fimbriae formation by STU1. In this study, the regulatory mechanism of in type 3 fimbriae formation was investigated. We found via quantitative RT-PCR that overexpression of enhanced the transcription level of the operon, which is involved in type 3 fimbriae synthesis, and reduced the transcription level of the operon, which is involved in type 1 fimbriae synthesis. To gain further insight into the role of in type 3 fimbriae synthesis, we analyzed the region upstream of the operon and found the potential cyclic 3'5'-adenosine monophosphate (cAMP) receptor protein (CRP) binding site. After was deleted in STU1 and two clinical isolates, these three mutant strains could not express MrkA, the major subunit of the fimbrial shaft, indicating that CRP positively regulated type 3 fimbriae synthesis. Moreover, a mutant overexpressing could not express MrkA, indicating that the regulation of type 3 fimbriae by was dependent on CRP. In addition, deletion of , which encodes the adenylyl cyclase that synthesizes cAMP, and deletion of , which encodes the glucose-specific EIIA, led to a reduction in operon regulation and therefore bacterial lactose uptake in . Exogenous cAMP but not overexpression compensated for the role of in bacterial lactose uptake. However, either overexpression or exogenous cAMP compensated for the role of in bacterial operon regulation that would eventually restore lactose uptake. We also found via ELISA and the reporter system that overexpression of increased intracellular cAMP levels and the transcription level of , respectively, in . In conclusion, overexpression of positively regulated cAMP production and cAMP-CRP activity to activate the operon, resulting in increased type 3 fimbriae synthesis in .