Fine tuning of virulence regulatory pathways in enteric bacteria in response to varying bile and oxygen concentrations in the gastrointestinal tract

Abstract

After entering the gastrointestinal (GI) tract on the way to their physiological site of infection, enteric bacteria encounter a remarkable diversity in environmental conditions. There are gross differences in the physico-chemical parameters in different sections of the GI tract e.g. between the stomach, small intestine and large intestine. Furthermore, even within a certain anatomical site, there are subtle differences in the microenvironment e.g. between the lumen, mucous layer and epithelial surface. Enteric pathogens must not only survive passage through the rapidly changing environments encountered at different niches of the GI tract but must also appropriately coordinate expression of virulence determinants in response to environmental cues at different stages of infection. There are some common themes in the responses of enteric pathogens to environmental cues, there are also distinct differences that may reflect differences in basic pathogenesis mechanisms. The role of bile and oxygen concentration in spatiotemporal regulation of virulence genes in selected enteric pathogens has been reviewed.

Gut Microbiota and Colonization Resistance against Bacterial Enteric Infection

“…The reason for the upregulation of flrA and downregulation of tcpA could be that the flagellum increases the speed of passing through the mucus layer, while the pilus would only slow it down. When lower concentrations of bile at the epithelial surface are encountered, expression can be reversed (214).…”

Survival of the Fittest: How Bacterial Pathogens Utilize Bile To Enhance Infection

“…In order to counteract the detergent-like properties of bile, both commensal and pathogenic E. coli strains activate stress responses, efflux pumps, and toxin/antitoxin systems to remove bile compounds (21,30,34). Stress response genes induced by bile salts, such as sulA, are used for the cessation of cell division in order to correct damage to DNA and the membrane following oxidative stress (21,(35)(36)(37), while efflux pump mechanisms, such as AcrAB-TolC, overcome bile acid toxicity and confer resistance to bile (38). A recent study demonstrated that the MqsR/MqsA toxin/antitoxin system degrades ygiS mRNA, which encodes a periplasmic protein that promotes the uptake of the bile salt deoxycholate by the bacteria and increases stress on the bacterial membrane (34).…”

Motility and biofilm formation of the emerging gastrointestinal pathogenCampylobacter concisusdiffers under microaerophilic and anaerobic environments

“…15,16 Previously Nielsen et al 17 detected both genomospecies in patients with diarrhea, though no CONTACT Susan V. Lynch susan.lynch@ucsf.edu association between genomospecies and clinical disease severity was observed. Environmental cues in the GI tract have previously been found to trigger virulence gene expression in pathogenic bacterial species such as Vibrio cholerae, 19 and may facilitate physiological reprogramming from commensalism to pathogenic states in opportunistic microbial species. One such environmental cue is oxygen availability, which has previously been reported to influence virulence in Gram negative bacteria, 19 such as Salmonella enterica serovar Typhimurium.…”

“…Environmental cues in the GI tract have previously been found to trigger virulence gene expression in pathogenic bacterial species such as Vibrio cholerae, 19 and may facilitate physiological reprogramming from commensalism to pathogenic states in opportunistic microbial species. One such environmental cue is oxygen availability, which has previously been reported to influence virulence in Gram negative bacteria, 19 such as Salmonella enterica serovar Typhimurium. 20 C. concisus can be cultured under microaerophilic and anaerobic conditions in laboratory settings and requires hydrogen for growth.…”