Pathogenicity

Ability to cause disease

Virulence

The extent of pathogenicity

Three ways a MO can infect a host

• Mucous membranes
• Respiratory tract
• GI tract
• Genitourinary tract
• Conjuctiva
• Skin
• Parenteral route

Portals of Entry: Respiratory tract

• Easiest
• Colds, pneumonia, tuberculosis, flu, measles, smallpox

Portals of Entry: Gastrointestinal tract

• Ingesting
• Most can be destroyed by stomach
• Poliomyelitis, hep A, typhoid fever, amoebic dysentery, giardiasis, shigellosis, cholera

Portals of Entry: Genitourinary tract

• Sexually transmitted
• May penetrate an unbroken mucous membrane
• Others require a cut or abrasion
• Herpes. HIV, genital warts, chlamydia, syphilis, gonorrhea

Portals of Entry: Skin

• Unbroken skin is excellent barrier
• Some gain access through an open wound

Portals of Entry: Parenteral Route

• Deposited beneath the skin
• Needles, punctures, bites, cuts, wounds, surgery

True or False: If an organism enters the body, it will produce a disease

False. Organisms have a preferred portal of entry therefore will not always produce disease.

ID₅₀

Infectious dose for 50% of the test population (virulence)

LD₅₀

Lethal dose (of a toxin) for 50% of the test population (potency of toxin)

Adhesion

• Surface molecules on MO that allow the MO to adhere to host tissue
• Glycocalyx, pili, fimbrae, flagella

Bioflim

• Communities of MO
• Scum in pools, shower doors, teeth

Capsule

• Glycocalyx can resist phagocytosis, therefore increases virulence
• Prevents adhesion of phagocytic cell

M protein

• Component of cell wall
• Acid and heat resistant

Extracellular enzymes

• Coagulase
• Kinases
• Hyaluronidase
• Collagenase
• IgA proteases

Coagulase

Coagulates blood

Kinase

Digests fibrin clots

Hyaluronidase

Hydrolyses hyaluronic acid

Collagenase

Hydrolyzes collagen

IgA proteases

Destroys IgA antibodies

Antigenic variation

Alter surface proteins

Invasins

Manipulate cytoskeleton allowing entry to cell membrane

Ways Bacterial Pathogens Can Damage Host Cells

• Use host nutrients
• Direct damage
• Producing toxins
• Inducing hypersensitivity reactions

Ways Bacterial Pathogens Can Damage Host Cells: Using host's nutrients

Siderophores: take iron from host iron-binding proteins

Ways Bacterial Pathogens Can Damage Host Cells: Direct damage

• Immediate area
• Use of nutrients
• Production of waste
• Rupture of cells

Ways Bacterial Pathogens Can Damage Host Cells: Toxins

• Toxin
• Toxigenicity
• Toxemia

Toxin

Poisonous substance produced by MO that contributes to pathogenicity

Toxigenicity

Ability to produce a toxin

Toxemia

Presence of toxin in host's blood

Exotoxins

• GRAM POSITIVE
• Produced inside the bacteria and released to surrounding medium

Toxoid

Inactivated toxin used in a vaccine

Antitoxin

Antibodies vs. a specific toxin

Characteristics of Exotoxins

• Genes carried on bacterial plasmids
• Soluble in bodily fluids
• Easily transported throughout body
• Among most lethal substances known
• I mg Botulinum = enough ExoT to kill 1 million Guinea Pigs
• Diseases are caused by ExoT, not bacteria themselves

Three types of Exotoxins

• B toxins (Type III)
• Membrane-disrupting (Type II)
• Superantigens (Type I)

B toxins

• Type III
• Two polypeptide components
• B for Binding
• A is enzyme

Membrane-disrupting toxins

• Type II
• Lyse host cells
• Make protein channels in the plasma membrane
• Disrupt phospholipid bilayer

Superantigens

• Cause intense immune response due to release of cytokines from host cells
• Fever, nausea, shock, vomiting, diarrhea, death

Classification of Exotoxins

• Cytotoxins
• Neurotoxins
• Enterotoxins

Cytotoxin

Kills cells or damages function

Neurotoxin

Alter nerve impulses

Enterotoxins

Affect GI tracts

Endotoxins

• GRAM NEGATIVE
• Lipopolysaccharides from outer membrane of G- bacteria
• All endotoxins produce same signs and symptoms
• Fever, ache, nausea, shock, blood clotting and death

Fever is caused by a

Pyrogenic response

Interleukins

• Released by macrophages
• Causes temperature to rise by affecting the hypothalamus

Ways virulence is enhanced

• Plasmids
• Lysogeny
• Pathogenicity

Viral Pathogenicity: Cytopathic effects

Observable signs of cell damage

Viral Pathogenicity: Cytocidal effects

Cell death

Fungi Pathogenicity

• Don't have well-defined set of factors
• Damage is usually by toxins
• Aflatoxin: carcinogenic fungus on peanuts

Protozoan Pathogenicity

• Presence of and waste produce disease symptoms
• Toxoplasma attaches to macrophages and gains entry by phagocytosis

Helminth Pathogenicity

• Presence produces disease
• Elephantitis

Algae Pathogenicity

• Few produce neurotoxin
• Saxitoxin: paralytic shellfish poisoning