13. Patogenicity

Transcription

13. Patogenicity

Microbial Mechanisms of Pathogenicity
Copyright © 2010 Pearson Education, Inc.
Mechanisms of Pathogenicity
 Pathogenicity: The ability to cause disease
 Virulence: The extent of pathogenicity
Portals of Entry




Mucous membranes
Skin
Parenteral route
Preferred portal of entry
Numbers of Invading Microbes
 ID50: Infectious dose for 50% of the test
population
 LD50: Lethal dose (of a toxin) for 50% of the test
population
Bacillus anthracis
Portal of Entry
Skin
ID50
10–50 endospores
Inhalation
10,000–20,000 endospores
Ingestion
250,000–1,000,000
endospores
Toxins
Agent
Botulinum
Shiga toxin
Staphylococcal enterotoxin
ID50
0.03 ng/kg
250 ng/kg
1350 ng/kg
Adherence
 Adhesins/ligands bind to receptors on host cells
 Glycocalyx: Streptococcus mutans
 Fimbriae: Escherichia coli
 M protein: Streptococcus pyogenes
 Form biofilms
Adherence
Figure 15.1
Adherence
Figure 15.1
Adherence
Figure 15.1
Capsules
 Prevent phagocytosis
 Streptococcus pneumoniae
 Haemophilus influenzae
 Bacillus anthracis
Cell Wall Components
 M protein resists phagocytosis
 Streptococcus pyogenes
 Opa protein inhibits T helper cells
 Neisseria gonorrhoeae
 Mycolic acid (waxy lipid) resists digestion
 Mycobacterium tuberculosis
Enzymes





Coagulase: Coagulates fibrinogen
Kinases: Digest fibrin clots
Hyaluronidase: Hydrolyzes hyaluronic acid
Collagenase: Hydrolyzes collagen
IgA proteases: Destroy IgA antibodies
Membrane Ruffling
Figure 15.2
Antigenic Variation
 Alter surface proteins
ANIMATION Virulence Factors: Hiding from Host Defenses
Figure 22.16
Penetration into the Host Cell
Cytoskeleton
 Invasins
 Salmonella
alters host
actin to enter
a host cell
 Use actin to
move from
one cell to
the next
 Listeria
Figure 15.2
Using the Host’s Nutrients:
Siderophores
 Use host’s iron
Figure 15.3
Direct Damage
 Disrupt host cell function
 Produce waste products
 Toxins
ANIMATION Virulence Factors: Penetrating Host Tissues
ANIMATION Virulence Factors: Enteric Pathogens
The Production of Toxins





Toxin: Substance that contributes to pathogenicity
Toxigenicity: Ability to produce a toxin
Toxemia: Presence of toxin in the host's blood
Toxoid: Inactivated toxin used in a vaccine
Antitoxin: Antibodies against a specific toxin
Exotoxins and Endotoxins
Figure 15.4
Exotoxins
 Specific for a structure or function in host cell
ANIMATION Virulence Factors: Exotoxins
Figure 15.4a
The Action of an A-B Exotoxin
Figure 15.5
Membrane-Disrupting Toxins
 Lyse host’s cells by
 Making protein channels in the plasma
membrane
– Leukocidins
– Hemolysins
– Streptolysins
 Disrupting phospholipid bilayer
Superantigens
 Cause an intense immune response due to
release of cytokines from host cells
 Symptoms: fever, nausea, vomiting,
diarrhea, shock, and death
Exotoxin
Source
Relation to microbe
Chemistry
Mostly Gram +
By-products of growing cell
Protein
Fever?
No
Neutralized by antitoxin?
Yes
LD50
Small
Figure 15.4a
Exotoxins & Lysogenic Conversion
Exotoxin
Corynebacterium
diphtheriae
A-B toxin
Lysogeny
+
Streptococcus
pyogenes
Membrane-disrupting
erythrogenic toxin
+
Clostridium botulinum
A-B toxin; neurotoxin
+
C. tetani
A-B toxin; neurotoxin
Vibrio cholerae
A-B toxin; enterotoxin
+
Staphylococcus
aureus
Superantigen
+
Endotoxins
Source
Relation to Microbe
Chemistry
Gram
Outer membrane
Lipid A
Fever?
Yes
Neutralized by Antitoxin?
No
LD50
Relatively large
Figure 15.4b
Endotoxins and the Pyrogenic
Response
Figure 15.6
Cytopathic Effects of Viruses
Figure 15.7
Cytopathic Effects of Viruses
Figure 15.8
Pathogenic Properties of Fungi
 Fungal waste products may cause symptoms
 Chronic infections provoke an allergic response
 Tichothecene toxins inhibit protein synthesis
 Fusarium
 Proteases
 Candida, Trichophyton
 Capsule prevents phagocytosis
 Cryptococcus
Pathogenic Properties of Fungi
 Ergot toxin
 Claviceps
 Aflatoxin
 Aspergillus
 Mycotoxins
 Neurotoxins: Phalloidin, amanitin
 Amanita
Pathogenic Properties of Protozoa
 Presence of protozoa
 Protozoan waste products may cause symptoms
 Avoid host defenses by
 Growing in phagocytes
 Antigenic variation
Pathogenic Properties of Helminths
 Use host tissue
 Presence of parasite interferes with host
function
 Parasite's metabolic waste can cause
symptoms
Pathogenic Properties of Algae
 Paralytic shellfish poisoning
 Dinoflagellates
 Saxitoxin
Figure 27.13
Portals of Exit
 Respiratory tract
 Coughing and sneezing
 Gastrointestinal tract
 Feces and saliva
 Genitourinary tract
 Urine and vaginal secretions
 Skin
 Blood
 Biting arthropods and needles or syringes
Mechanisms of Pathogenicity
Figure 15.9

13. Patogenicity

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