Hi, i want to ask, what is the difference between commensal and pathogenic bacteria invasion pathway? Does this two type of bacteria Invade in colonic epithelial cell in the same way? by binding what kind of receptor ? or some specific molecules involved in the invasion pathway in this two type of bacteria? Thanks!
Dear Xin Wang
This depend on type of the virulence factor found in strain and gene expression
Dear Xin Wang,
Please see attached file. Hope you find your answers.
Intrinsically, commensals are non invasive. What distinguishes them from pathogens is that the latter group expresses genes that confer pathogenecity. For eg. the pathogenicity islands that are part of many pathogens such as Salmonella (eg type III secretion system) are well known. These components are missing in commensals. However, any breach in the intestinal epithelium would indicate pathogenic infiltration which alarms the immune system to mount a response. Particularly in the context of epithelial cells, a commensal bacterium can become pathogenic if there is a damage to the epithelial barrier. The pathogenic bacterium C. difficile can manipulate the epithelial tight junction barrier functions and can invade tissues. In addition, there are also may bacterial pathogens that are intracellular. Broadly, there is no intrinsic property that defines a microbe as either a commensal or pathogen and largely it seems to be dictated by immune state of the host or danger signals of tissue damage. So broadly speaking, I would predict that these two groups do not share a common invasion pathway. What is more interesting is the ability of the innate immune system to recognize and mount an appropriate response against commensals (tolerogenic response) vs pathogens (inflammatory response). For eg. LPS component is a pathogen associated molecular pattern (PAMP) that is present in both commensals as well as pathogens and is recognized by the pattern recognition receptors (PRRs) (such as TLRs) expressed by the host. So using the term "microbe associated molecular pattern" (MAMP) would be more appropriate than PAMP. I tried to answer your question in the context of immune response but I hope it is useful.
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