The GadX regulon affects virulence gene expression and adhesion of porcine enteropathogenic Escherichia coli in vitro

Abstract

The ability of enteropathogenic Escherichia coli (EPEC) to express virulence factor genes and develop attaching and effacing (AE) lesions is inhibited in acidic environmental conditions. This inhibition is due to the activation of transcription factor GadX, which upregulates expression of glutamic acid decarboxylase (Gad). Gad, in turn, produces γ-aminobutyric acid (GABA), which was recently shown to have a beneficial effect on the jejunal epithelium in vitro due to increased mucin-1 levels. In the present study, we sought to test whether forced GadX activation/overexpression abolishes virulence associated features of EPEC and provokes increased GABA production. EPEC strains were isolated from diarrheic pigs and submitted to activation of GadX by acidification as well as gadX overexpression via an inducible expression vector plasmid. GABA concentrations in the growth medium, ability for adhesion to porcine intestinal epithelial cells (IPEC-J2) and virulence gene expression were determined. Growth in acidified media led to increased GABA levels, upregulated gadA/B expression and downregulated mRNA synthesis of the bacterial adhesin intimin . EPEC strains transformed with the gadX gene produced 2.1–3.4-fold higher GABA levels than empty-vector controls and completely lost their ability to adhere to IPEC-J2 cells and to induce actin accumulation. We conclude that intensified gadX activation can abolish the ability of EPEC to adhere to the intestinal epithelium by reducing the expression of major virulence genes.

Potential Probiotic Bacillus subtilis Isolated from a Novel Niche Exhibits Broad Range Antibacterial Activity and Causes Virulence and Metabolic Dysregulation in Enterotoxic E. coli

“…Furthermore, metabolites that appeared in high concentrations in ETEC mono-cultures were significantly regulated in the co-culture, suggesting that CP9 may influence ETEC cellular metabolism and growth. For example, secondary metabolite gamma-Aminobutyric acid (GABA), which is responsible for spore germination, bile and low pH resistance, and tight regulation of virulent factors in enterotoxic and enteropathogenic E. coli [ 77 , 78 ], was observed in significantly lower abundance in the co-culture compared to ETEC mono-culture. This data is further supported by the lower cell number of ETEC after the co-culture.…”

Analysis of Growth Phases of Enterotoxigenic Escherichia coli Reveals a Distinct Transition Phase before Entry into Early Stationary Phase with Shifts in Tryptophan, Fucose, and Putrescine Metabolism and Degradation of Neurotransmitter Precursors

“…The AraC-like transcription factor GadX is an activator of the glutamate decarboxylase gadAB that converts l-glutamate to GABA. GadX is also a repressor of the transcription factor that activates the expression of adhesion factor bundle forming pilus ( bfp ) and intimin in enteropathogenic E. coli ( 45 , 46 ). Hence, factors that increase GABA might also downregulate virulence factors, and the corresponding rapid degradation of GABA at the transient phase could promote virulence and downregulated immune responses to ETEC.…”

Regulation of Escherichia coli fim gene transcription by GadE and other acid tolerance gene products

“…Several studies have shown that GadX regulates a number of genes in enteropathogenic E. coli, including the per gene that encodes the Per regulatory protein [77][78][79]. GadW can complex with GadE to regulate enterohemorrhagic E. coli virulence factor genes [80].…”