Chapter 15: Lecture: Part 1

Microbial Mechanisms of Pathogenicity

pathogenicity

• the ability to cause disease

virulence

• the degree of pathogenicity

portal of entry

• mucous membranes (eyes, nose, mouth, sexual contact

• skin/wound

• parenteral route

  • deposited directly into tissues when barriers are penetrated

True or False: Most pathogens have a preferred portal of entry

true

Define ID50 and what does it measure?

• infectious dose for 50% of sample population (or tissue or cell)

  • measures virulence of a microbe

LD50 and what does it measure ?

• lethal dose for 50% of sample population (or tissue or cell)

  • measures potency of a toxin

Almost all pathogens attach to host tissues in a process known as what ?

• Adherence or adhesion

an accessory in a pathogen that helps it bind to receptors in the host cells

• adhesins (ligand)

Where can you find adhesins ?

1. in glycocalyx (biofilm, capsules)

2. fimbriae

3. pili

What does b) and c) depict ?

b) antibodies normally function by binding to antigens, molecules on the surface of pathogenic bacteria. Phagocytes then bind to the antibody, initiating phagocytosis

c) some bacteria also produce proteases, virulence factors that break down host antibodies to evade phagocytosis

Name bacteria with capsules

• Yes,- Yersinia pestis

• Some- Streptococcus pneumoniae

• Killers- Klebsiella pneumoniae

• Have- Haemophilus influenza

• Pretty- Pseudomonas aeruginosa

• Nice- Neisseria meningitidis

• Capsule- Cryptococcus neoformans

Cell Wall Components

• M Protein resists phagocytosis

• Opa protein allows attachment to host calls

• Waxy lipid (mycolic acid) resist digestion

Give an example of an organism that contains an M protein

• Streptococcus Pygoenes

Give an example of an organism that contains an opa protein

• Neisseria gonorrhoeae

Give an example of an organism that contains waxy lipid

• Mycobacterium tuberculosis

Coagulase

• coagulate fibrinogen

Kinases

• digest fibrin clots

Hyaluronidase

• digests polysaccharides that hold cells together

Collagenase

• breaks down collagen

IgA protease

• destroy IgA antibodies

Streptokinase

How does Antigenic Variation work?

• Pathogens alter their surface antigens

• Antibodies are rendered ineffective

• Vaccines are less effective

Give examples of species that demonstrate antigenic variation

• Trypanosoma sp.

• Influenza

• Covid-19

Antigenic drift

Antigenic shift

Penetration into the Host Cell Cytoskeleton

• Invasins

  • Surface proteins produced by bacteria that rearrange actin filaments of the cytoskeleton

    • cause membrane ruffling

Give examples of species that use actin to move from one cell to the next

• Shigella sp.

• Listeria sp.