Chapter 15 Terms

Pathogenicity

The ability to cause disease

Virulence

The degree of pathogenicity

Portals of Entry

Most pathogens have a preferred portal of entry, this is how they enter the host.

Mucous Membranes

The most commonly used portal of entry: Respiratory tract (inhalation)

Others:

• Digestive canal: organisms in food, water and on contaminated fingers

• Genital system: portal of entry for STIs

Skin

Unbroken skin is impenetrable by most organisms.

• Possible entry points: hair follicles, sweat glands ducts

Parenteral Route

Deposited directly into tissues when barriers are penetrated

• Injections, bites, wounds, cuts, surgery

ID50

The infectious dose for 50% of a sample population

• This measures the virulence of a microbe (only works for living organisms)

LD50

The lethal dose for 50% of a sample population

• Measures potency of a toxin (want number to be higher)

Adherence (Adhesion)

A process almost all pathogens use to attach to host tissues

• Viral spikes

• Fimbriae

• Adhesions (Ligands) - bind to receptors on the host cells

Capsules

A glycocalyx formed around the cell wall

• This impairs phagocytosis

M Protein

• Resists phagocytosis

Lipopolysaccharide (LPS)

Found in gram negative cells

• Activates immune system response

Coagulases (Enzyme)

Coagulate fibrinogen forming fibrin which creates a barrier to protect bacterial cells

Hyaluronidase (Enzymes)

Digest hyaluronic acid, breaks down the ECM

• Causes skin to “fall off”

IgA proteases (Enzymes)

Destroy IgA antibodies, destroys your defense system

Antigenic Variation

Pathogens alter their surface antigens; the antibodies that a host made against those antigens are rendered ineffective

• Most common example: Influenza virus

Methods of Penetration into the Host

• Invasins -

  • Surface proteins produced by bacteria that rearrange actin filaments of the cytoskeleton - this causes membrane ruffling which results in the bacteria being engulfed

  • Use actin to more from one cell to the next (Shigella and Listeria)

  • Survival inside phagocytes

Biofilms

• Resistant to antibiotics and disinfectants

• Involved in 65% of all infections

• Play role in evading phagocytes - bacteria are shielded by extracellular polymeric substance of biofilm

Siderophores

• Uses the host’s nutrients, specifically iron

• Proteins secreted by pathogens that bind iron more tightly than host cells and host iron-binding proteins

Direct Damage

• Disrupts host cell function

• Uses host cell nutrients

• Produces waste products

• Multiplies in host cells and causes ruptures

Toxins

Poisonous substances produced by microorganisms

• Produce fever, cardiovascular problems, diarrhea, and shock

Toxemia

Presence of toxin in the host’s blood

Intoxications

A presence of toxin without microbial growth - usually ingested

Exotoxins

These are proteins produced and secreted by bacteria

• Soluble in bodily fluids; destroy host cells and inhibit metabolic functions

• Highly specific for their targets

• Some can be highly lethal

Antitoxins

Antibodies against specific exotoxins that provide immunity

• Binds to toxin and neutralizes it

A-B toxins

Contain an enzyme component (A part) and a binding component (B part)

How it works: The B part assists the enzyme component in finding its binding site.

Genotoxins

• Damage DNA (causing mutations, disrupting cell division, may lead to cancer)

Endotoxins

Lipid A portion of LPS is the only endotoxin

• Endotoxins cause damage indirectly

• It is released during bacterial multiplication and when gram-negative bacteria die - this stimulates macrophages to release large quantities of cytokines

• Cause endotoxin shock, fevers, chills, weakness, generalized aches, may weaken blood brain barrier