Microbial Mechanisms of Pathogenicity

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Microbiology
Chapter 15
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1

Pathogenicity

Ability to cause disease

2

Virulence

The extent of pathogenicity

3

Three ways a MO can infect a host

  • Mucous membranes
  • Respiratory tract
  • GI tract
  • Genitourinary tract
  • Conjuctiva
  • Skin
  • Parenteral route
4

Portals of Entry: Respiratory tract

  • Easiest
  • Colds, pneumonia, tuberculosis, flu, measles, smallpox
5

Portals of Entry: Gastrointestinal tract

  • Ingesting
  • Most can be destroyed by stomach
  • Poliomyelitis, hep A, typhoid fever, amoebic dysentery, giardiasis, shigellosis, cholera
6

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
7

Portals of Entry: Skin

  • Unbroken skin is excellent barrier
  • Some gain access through an open wound
8

Portals of Entry: Parenteral Route

  • Deposited beneath the skin
  • Needles, punctures, bites, cuts, wounds, surgery
9

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.

10

ID50

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

11

LD50

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

12

Adhesion

  • Surface molecules on MO that allow the MO to adhere to host tissue
  • Glycocalyx, pili, fimbrae, flagella
13

Bioflim

  • Communities of MO
  • Scum in pools, shower doors, teeth
14

Capsule

  • Glycocalyx can resist phagocytosis, therefore increases virulence
  • Prevents adhesion of phagocytic cell
15

M protein

  • Component of cell wall
  • Acid and heat resistant
16

Extracellular enzymes

  • Coagulase
  • Kinases
  • Hyaluronidase
  • Collagenase
  • IgA proteases
17

Coagulase

Coagulates blood

18

Kinase

Digests fibrin clots

19

Hyaluronidase

Hydrolyses hyaluronic acid

20

Collagenase

Hydrolyzes collagen

21

IgA proteases

Destroys IgA antibodies

22

Antigenic variation

Alter surface proteins

23

Invasins

Manipulate cytoskeleton allowing entry to cell membrane

24

Ways Bacterial Pathogens Can Damage Host Cells

  • Use host nutrients
  • Direct damage
  • Producing toxins
  • Inducing hypersensitivity reactions
25

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

Siderophores: take iron from host iron-binding proteins

26

Ways Bacterial Pathogens Can Damage Host Cells: Direct damage

  • Immediate area
  • Use of nutrients
  • Production of waste
  • Rupture of cells
27

Ways Bacterial Pathogens Can Damage Host Cells: Toxins

  • Toxin
  • Toxigenicity
  • Toxemia
28

Toxin

Poisonous substance produced by MO that contributes to pathogenicity

29

Toxigenicity

Ability to produce a toxin

30

Toxemia

Presence of toxin in host's blood

31

Exotoxins

  • GRAM POSITIVE
  • Produced inside the bacteria and released to surrounding medium
32

Toxoid

Inactivated toxin used in a vaccine

33

Antitoxin

Antibodies vs. a specific toxin

34

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
35

Three types of Exotoxins

  • B toxins (Type III)
  • Membrane-disrupting (Type II)
  • Superantigens (Type I)
36

B toxins

  • Type III
  • Two polypeptide components
  • B for Binding
  • A is enzyme
37

Membrane-disrupting toxins

  • Type II
  • Lyse host cells
  • Make protein channels in the plasma membrane
  • Disrupt phospholipid bilayer
38

Superantigens

  • Cause intense immune response due to release of cytokines from host cells
  • Fever, nausea, shock, vomiting, diarrhea, death
39

Classification of Exotoxins

  • Cytotoxins
  • Neurotoxins
  • Enterotoxins
40

Cytotoxin

Kills cells or damages function

41

Neurotoxin

Alter nerve impulses

42

Enterotoxins

Affect GI tracts

43

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
44

Fever is caused by a

Pyrogenic response

45

Interleukins

  • Released by macrophages
  • Causes temperature to rise by affecting the hypothalamus
46

Ways virulence is enhanced

  • Plasmids
  • Lysogeny
  • Pathogenicity
47

Viral Pathogenicity: Cytopathic effects

Observable signs of cell damage

48

Viral Pathogenicity: Cytocidal effects

Cell death

49

Fungi Pathogenicity

  • Don't have well-defined set of factors
  • Damage is usually by toxins
  • Aflatoxin: carcinogenic fungus on peanuts
50

Protozoan Pathogenicity

  • Presence of and waste produce disease symptoms
  • Toxoplasma attaches to macrophages and gains entry by phagocytosis
51

Helminth Pathogenicity

  • Presence produces disease
  • Elephantitis
52

Algae Pathogenicity

  • Few produce neurotoxin
  • Saxitoxin: paralytic shellfish poisoning