Question

what are the ways in which an organism can evade phagocytosis?

Answer 1

-Pathogens may invade or get confined in areas which are inaccessible to phagocytes like urninary bladder or unbroken skin .
-Pathogens may have the ability to avoid an overwhelming inflammatory response. When there is no inflammation, the host cannot generate phagocytic defenses.
-Some bacteria or products inhibit phagocyte chemotaxis. For example, streptococcal streptolysine (which also kills phagocytes) suppresses neutrophil chemotaxis, even at very low concentrations.
- Some pathogens cover the surface of the bacterial cell with a self component" such as the structure of the host phagocytes and the immune system. This leads to the antigenic surface being hidden Phagocytes cannot recognize bacteria after contact and thus the oocurence of phagocytosis is decreased. For example, pathogenic Staphylococcus aureus produces cell-bound coagulase and clumping factor which clots fibrin on the bacterial surface of the bacterial cell with a component that is seen by the host phagocytes and the immune system as "self." This strategy hides the antigenic surface of the bacterial cell. Phagocytes cannot recognize bacteria upon contact and the possibility of opsonization by antibodies to enhance phagocytosis is minimized. For example, pathogenic Staphylococcus aureus produces cell-bound coagulase and clumping factor which clots fibrin on the bacterial surface. Treponema pallidum, the agent of syphilis, binds fibronectin to its surface. Group A streptococci can synthesize a hyaluronic acid capsule. Hyaluronic acid is the ground substance (tissue cement) of the connective tissue. Some pathogens have or can deposit sialic acid residues on their surfaces, which prevent opsonization by complementary components and prevent the

Inhibition of Phagocytic Engulfment -

pathogenic bacteria bear on their surfaces substances that may inhibt engulfment by a phagocyte. Resistance to phagocytosis could be due to
- Polysaccharide capsules of S. pneumoniae, Haemophilus influenzae
- M protein and fimbriae of Group A streptococci
- Surface slime (polysaccharide) produced as a biofilm byPseudomonas aeruginosa
- O polysaccharide associated with LPS of E. coli
- K antigen (acidic polysaccharides) of E. coli or the analogous Vi antigen of Salmonella typhi
Survival Inside of Cells:-
Some bacteria survive inside of phagocytes, either neutrophils or macrophages. Some organisms can resist being swallowed up and killed and survive or multiply in phagocytes. They then espcape and infect new organisms
Products of bacteria or viruses may produce aggresins which are substances that kill or inactivate phagocytes.