Microbial Mechanisms of Pathogenicity

How microorganisms enter & exit a host

Portals of Entry

Mucous membranes

gastrointestinal tract

respiratory tract

Skin

sweat gland ducts

hair follicles

Parenteral route

wounds

njections

The Preferred Portal of Entry

Salmonella typhi

swallowed

Streptococci

inhaled

Bacillus anthracis

multiple portal of entry

Numbers of Invading Microbes

LD50

ID50

Adherence

Glycocalyx

Streptococcus mutans

Fimbriae

Escherichia coli

M protein

Streptococcus pyogenes

Portals of Exit

How Pathogens Damage Host Cells

Using the Host’s Nutrients

siderophores

receptors

Direct Damage

Disrupt host cell function

Produce waste products

Toxins

Endotoxins

cytokines

Exotoxins

A-B toxins

A-part (enzyme)

B-part (the binding)

membrane-disrupting toxins

lysis the host cells

Making protein channels

Disrupting phospholipid bilayer

superantigens

How Pathogens Penetrate Host Defenses

Capsules

Bacillus anthracis

Streptococcus pneumoniae

Haemophilus influenzae

Cell Wall Components

M protein

Opa-protein

Mycolic acid

Enzymes

Coagulase

Kinases

Hyaluronidase

Actin in cytoskeleton

Antigenic Variation