Download Chapter 12: Microbial Pathogenicity

Chapter 12: Microbial Pathogenicity
• Pathogenicity
The ability to cause disease
• Virulence
The extent of pathogenicity
Portals of Entry
• Mucous membranes
• Skin
• Parenteral route
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
Adherence of Microbe
• Adhesins/ligands bind to receptors on host cells
• Glycocalyx
Streptococcus mutans
• Fimbriae
Escherichia coli
•
Streptococcus pyogenes
•
Neisseria gonorrhoeae
Pathogenicity Promoters
•
Coagulates blood
•
Digests fibrin clots
• Hyaluronidase
Hydrolyzes hyaluronic
acid
• Collagenase
Hydrolyzes collagen
Pathogenicity Promoters
• IgA proteases
Destroy IgA antibodies
• Siderophores
Take iron from host ironbinding proteins
•
Alter surface proteins
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Penetration into the Host Cell
Figure 15.2
Toxins
• Toxin
Substances that contribute to
pathogenicity
• Toxigenicity
Ability to produce a toxin
• Toxemia
Presence of toxin in the host's blood
• Toxoid
Inactivated toxin used as a vaccine
• i.e. diptheria and tetanus toxoid
• Antitoxin
Antibodies against a specific toxin
Endotoxin
Figure 15.4b
Endotoxin
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Endotoxins
Figure 15.6
Endotoxins
Source
Gram negative bacteria
Location
Outer membrane
Chemistry
Lipopolysaccharide (LPS) → Lipid A
Fever?
Yes
Neutralized by antitoxin
No
LD50
Relatively large
Exotoxins
Figure 15.4a
Types of Exotoxins
•
• Cause an intense immune response due to release
of cytokines from host cells
• Fever, nausea, vomiting, diarrhea, shock, death
•
Types of Exotoxins
• Membrane-disrupting toxins
• Lyse host cells by:
• Making protein channels in the plasma
membrane (e.g.,
• Disrupting phospholipid bilayer
• S. aureus and Streptococci
)
Types of Exotoxins
• A-B toxins
• Disrupts internal cellular
mechanisms;
• Clostridium botulinum
produces an A-B
neurotoxin
• Vibrio cholerae produces
an A-B enterotoxin
Figure 15.5
Exotoxins
Exotoxin
Lysogenic
conversion
• Clostridium botulinum
A-B toxin - Neurotoxin
+
• Vibrio cholerae
A-B toxin - Enterotoxin
+
Exotoxin
Source
Mostly Gram positive
location
Secreted by cell
Chemistry
Fever?
Neutralized by antitoxin
LD50
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Protein
Type I (Superantigens)
Yes
Small
Pathogenic Properties of Fungi
• Fungal metabolic waste products may cause allergies
• Proteases
•
• Vaginal yeast infection
• Capsule prevents phagocytosis
•
LINK
• Can cause skin or nervous tissue disease
• Found in soil and pigeon droppings
Pathogenic Properties of Fungi
•
Aflatoxin; second link
•
Aspergillus flavus
•
•
•
Infrequently, contaminated peanut butter recalled
Neurotoxins
•
•
•
mushrooms
May be fatal if ingested
Ergot toxin
•
Claviceps purpurea
Pathogenic Properties of Protozoa
• Avoid host defenses by
• Growing inside host cell
• i.e.
• Antigenic variation
• Avoiding host immune system
•
campers: be careful what you
drink!
Pathogenic Properties of Helminths
• Presence of parasite may interfere with host function
• i.e.
vessels link
parasite clogs lymphatic
Pathogenic Properties of Algae
• Neurotoxins produced by
- Paralytic shellfish poisoning
Portals of Exit
• Respiratory tract
• Coughing, sneezing
• Gastrointestinal tract
• Feces, saliva
• Genitourinary tract
• Urine, vaginal secretions, semen
• Skin
• Skin infections
• Blood
• Biting arthropods, needles/syringes
Mechanisms of Pathogenicity