Question

3.Explain how each of these virulence factors contributes to the pathogenesis of E. coli:

a.P fimbria

b.Hemolysins and siderophores:

c.Capsule (K antigen)

d.Heat-labile enterotoxin (LT) and heat stable toxin (ST):

e.Shiga toxins:

Answer 1

a.P fimbria: These are appendages found on the surface of E. coil. They play an important role in virulence of E. coli. during urinary tract infection by mediated the adherence to the host uroepithelial cells and help in colonization, thereby resisting the elimination by the flow of urine.

b.Hemolysins and siderophores: Hemolysins cause lysis of host red blood cells by forming the pores in their cell membrane. This strategy could be used to obtain iron by lysing and releasing the substances from red blood cells. Hemolysins produced by E. coli. cause lysis of monocytes, macrophages and lymphocytes.

Siderophores help in the assimilation of iron. They compete for iron with host iron-binding proteins. Siderophore bound iron is taken up by bacterial receptors for iron utilization.

c.Capsule (K antigen): They are composed of polysaccharides and surround the surface of E. coli. They decrease the ability of antibodies to bind to the bacterial surface resulting in increased virulence. They also decrease the ability of phagocytes to recognize and engulf the bacterial cells.

d.Heat-labile enterotoxin (LT) and heat stable toxin (ST): They are toxic secretory peptides. In E. coli. they are known to interact with membrane-associated guanylyl cyclase resulting in the production of cGMP, which affects several downstream signalling pathways. These events lead to increased water loss and diarrhoea. They are also known to increase the adherence of pathogen.  

e.Shiga toxins: It consists of two subunits, A and B. A subunit halts protein synthesis by injuring ribosomes. While, B subunit binds to the cellular receptor on endothelial cells,