Question

Bacterial Quorum Sensing, Pathogenicity Islands, and Secretion Systems

1.bacterial quorum sensing may play a role in pathogenicity by:

a) Promoting initial colonization of a new host;

b) Enabling the bacterium to persist within that host; and

c) Allowing some of the bacteria to spread to a new location within a host or to a new host.

Question: Briefly describe how the ability to produce a type 3 secretion system might play a role in a pathogen colonizing the body and causing an infection.

Answer 1

ans). Type III secretion systems is a complex bacterial function that enable pathogens with unique virulence mechanism to inject bacterial effector proteins directly into the host cell cytoplasm, bypassing the extracellular milieu(needle like structure).

• Effector proteins vary based on type of secreting pathogens, common pathogenic mechanisms includes interference with the host cell cytoskeleton to promote attachment and invasion of bacterial effector molecules.
• The activity of the Type 3 Secretion System correlates with infection progression and outcome, in animal models and also human infection.

By establishment of the pathogen at the appropriate portal of entry in host organisms leads to colonization of pathogens.

• Pathogens usually colonize host tissues that are in contact with the external environment.
• Pili, is a  polymeric hair-like struture protruding from the surface of bacteria, involved in the binding of bacteria to host cells.
• Bacterias involved in infection have the ability to involve in the the functions of the host cell to the benefit of the bacterium by altering cellular communication of host.

Image below shows the type 3 secretion system also colonization and infection in host cell.

A secretion apparatus in the cytoplasmic membrane and cell wall of the bacterium polymerizes a hollow needle that is lowered to the cytoplasmic membrane of the host cell and a translocon protein is then delivered to anchor the needle to the host cell. Effector proteins in the bacterium can now be injected into the cytoplasm of the host cell. The delivery system is sometimes called an injectisome.

Type3 secretion system is used by various pathogenic bacteria including Salmonella, Shigella, Yersinia, Ecoli and Pseudomonas aeruginosa.

Type3 Secretion System is genetically, structurally and functionally related to bacterial flagella. This system contains more than 20 different proteins. All this together form a huge structure crossing the bacterial cell envelope and reaching host cell.

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