bacterial virulence

Bacterial Virulence Factors

Prof. Nesrene Salah Omar

Objectives

•Microbial Mechanisms of Pathogenic

•Microbes and humans •Virulence factors•Host - parasite Interaction•Bacterial Virulence Factors

Microbial Mechanisms of Pathogenic

Microbes and humans

Very few microbes arealways pathogenic

Many microbes arepotentially pathogenic

Most microbes arenever pathogenic

Host - parasite Interaction

Intracellular

Eukaryotic Cell

Receptor

Virulent Bacteria

Prokaryotic Cell

Control of virulence factors:(Pilin, capsule, invasins, toxins etc)

Adherence blockers

Pili or adhesins

Prokaryotic and Eukaryotic Interactions

Intracellular

Eukaryotic Cell

Receptor

Virulent Bacteria

Prokaryotic Cell

Control of virulence factors:(Pilin, capsule, invasins, toxins etc)

COLONIZATION

Adherence blockers

Pili or adhesins

Prokaryotic and Eukaryotic Interactions

Intracellular

Eukaryotic Cell

Receptor

Virulent Bacteria

Prokaryotic Cell

Control of virulence factors:(Pilin, capsule, invasins, toxins etc)

COLONIZATION INVASION

Adherence blockers

Pili or adhesins

Virulence

The ability of an agent of infection to produce disease.

The virulence of a microorganism is a measure of the severity of the disease it causes.

Bacterial Virulence Factors

Virulence factors help bacteria • invade the host• cause disease• evade host defenses.

Include:1. Attachment (via adhesins)2. Colonization3. Invasiveness4. Toxins & Enzymes5. Inhibition of Phagocytosis

1-Attachment (via adhesins)

They allow bacteria to bind to host cells :

• fimbriae • some bacterial cell

walls • capsules

These adhesins bind to specific epithelium receptors or they are able to maintain even closer contact.

Cilia - motion

Flagellum - motion

A

B

DCell Parts

Flagellum - motion

Cell Wall – protection, invasion, evasion

Ribosome – production of toxins/attachment proteins on cell wall

Cilia - motion

2-Colonization

• The Ability to Adhere to Host Cells and Resist Physical Removal or

• the establishment of the pathogen at the appropriate portal of entry.

• Pathogens usually colonize host tissues that are in contact with the external environment.

Virulence Factors that Promote Bacterial Colonization:

1. Using Pili (fimbriae) to Adhere to Host Cells

2. Using Adhesins to Adhere to Host Cells

3. Using Biofilms to Adhere to Host Cells

3-Invasiveness

• the ability of a pathogen to invade tissues. • Invasiveness encompasses

(1) mechanisms for colonization (adherence and initial multiplication),

(2) production of extracellular substances ("invasins"), that promote the immediate invasion of tissues

(3) ability to bypass or overcome host defense mechanisms which facilitate the actual invasive process.

Invasiveness

• Hyaluronidase

• Coagulase

• Streptokinase

(dissolves Clots)

4-Toxins &EnzymesToxins• They are products of a

pathogen that destroy/damage/

• inactivate one or more vital component of the host.

• Classes of toxinsNeurotoxinsEnterotoxins Cytotoxins

EnzymesExcretion of certain

pathogens to assist them in establishing infection and producing a disease.

There are virulence

determinant enzymes that dissolve the glue between cells, thus allowing the bacteria to spread rapidly through the tissue.

5-Inhibition of PhagocytosisPhagocytosis

Inhibition of Phagocytosis

• Ability of Pathogens to Avoid or Overcome Phagocytes

• Avoiding Contact with Phagocytes

• Inhibition of Phagocytic Engulfment

• Survival Inside of Cells

Summary Virulence factors

Thank you