Regulation of fim genes in uropathogenic Escherichia coli

Uropathogenic Escherichia coli(UPEC)is the leading cause of urinary tract infections in women,causing significant morbidity and mortality in this population.Adherence to host epithelial cells is a pivotal step in the pathogenesis of UPEC.One of the most important virulence factors involved in mediating this attachment is the type 1 pilus(type 1 fimbria)encoded by a set of fim genes arranged in an operon.The expression of type 1 pili is controlled by a phenomenon known as phase variation,which reversibly switches between the expression of type 1 pili(Phase-ON)and loss of expression(Phase-OFF).Phase-ON cells have the promoter for the fimA structural gene on an invertible DNA element called fimS,which lines up to allow transcription,whereas transcription of the structural gene is silenced in Phase-OFF cells.The orientation of the fimS invertible element is controlled by two site-specific recombinases,FimB and FimE.Environmental conditions cause transcriptional and post-transcriptional changes in UPEC cells that affect the level of regulatory proteins,which in turn play vital roles in modulating this phase switching ability.The role of fim gene regulation in UPEC pathogenesis will be discussed.

GadE regulates fliC gene transcription and motility in Escherichia coli

BACKGROUND Escherichia coli(E.coli)express flagella to ascend human urinary tracts.To survive in the acidic pH of human urine,E.coli uses the glutamate decarboxylase acid response system,which is regulated by the GadE protein.AIM To determine if growth in an acidic pH environment affected fliC transcription and whether GadE regulated that transcription.METHODS A fliC-lacZ reporter fusion was created on a single copy number plasmid to assess the effects of acidic pH on fliC transcription.Further,aΔgadE mutant strain of a uropathogenic E.coli was created and tested for motility compared to the wildtype strain.RESULTS Escherichia coli cells carrying the fliC-lacZ fusion displayed significantly less fliC transcription when grown in an acidic pH medium compared to when grown in a neutral pH medium.Transcription of fliC fell further when the E.coli was grown in an acidic pH/high osmolarity environment.Since GadE is a critical regulator of one acid response system,fliC transcription was tested in a gadE mutant strain grown under acidic conditions.Expression of fliC was derepressed in the E.coli gadE mutant strain grown under acidic conditions compared to that in wild-type bacteria under the same conditions.Furthermore,a gadE mutation in a uropathogenic E.coli background exhibited significantly greater motility than the wild-type strain following growth in an acidic medium.CONCLUSION Together,our results suggest that GadE may down-regulate fliC transcription and motility in E.coli grown under acidic conditions.

Osmolyte transport in Staphylococcus aureus and the role in pathogenesis

Osmolyte transport is a pivotal part of bacterial life, particularly in high salt environments. Several low and high affinity osmolyte transport systems have been identified in various bacterial species. A lot of research has centered on characterizing the osmolyte transport systems of Gram-negative bacteria, but less has been done to characterize the same transport systems in Gram-positive bacteria. This review will focus on the previous work that has been done to understand the osmolyte transport systems in the species Staphylococcus aureus and how these transporters may serve dual functions in allowing the bacteria to survive and grow in a variety of environments, including on the surface or within humans or other animals.

Mutations of the brpR and brpS genes affect biofilm formation in Staphylococcus aureus

BACKGROUND In the United States,Staphylococcus aureus(S.aureus)kills tens of thousands of individuals each year and the formation of a biofilm contributes to lethality.Biofilm-associated infections are hard to treat once the biofilm has formed.A new stilbene drug,labeled SK-03-92,was shown to kill S.aureus and affected transcription of two genes tied to a putative two-component system(TCS)we have named brpR(biofilm regulating protein regulator)and brpS(biofilm regulating protein sensor).AIM To determine if BrpR and BrpS regulate biofilm formation,brpR and brpS mutants were assessed using biofilm assays compared to wild-type S.aureus.METHODS A combination of biofilm and quantitative real-time-polymerase chain reaction assays were used.In addition,bioinformatic software tools were also utilized.RESULTS Significantly more biofilm was created in the brpR and brpS mutants vs wild-type cells.Quantitative real-time polymerase chain reactions showed the brpS mutant had differences in transcription of biofilm associated genes that were eight-fold higher for srtA,two-fold lower for lrgA,and 1.6-fold higher for cidA compared to wild-type.Bioinformatic analysis demonstrated that the S.aureus brpR/brpS TCS had homology to streptococcal late-stage competence proteins involved in celldeath,increased biofilm production,and the development of persister cells.CONCLUSION Our study suggests that brpR/brpS is a TCS that may repress S.aureus biofilm production and be linked to late-stage competence in S.aureus.