Chapter 12: Microbial Pathogenicity
• Pathogenicity The ability to cause disease
• Virulence The extent of pathogenicity
• Mucous membranes
• Skin
• Parenteral route
Portals of Entry
• ID50: Infectious dose for 50% of the test population
• LD50: Lethal dose (of a toxin) for 50% of the test population
Numbers of Invading Microbes
Bacillus anthracis
Portal of entry ID50
Skin 10-50 endospores
Inhalation 10,000-20,000 endospores
Ingestion 250,000-1,000,000 endospores
• Adhesins/ligands bind to receptors on host cells
• Glycocalyx Streptococcus mutans
• Fimbriae Escherichia coli
• Streptococcus pyogenes
• Neisseria gonorrhoeae
Adherence of Microbe
• Coagulates blood
• Digests fibrin clots
• Hyaluronidase Hydrolyzes hyaluronic acid
• Collagenase Hydrolyzes collagen
Pathogenicity Promoters
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Pathogenicity Promoters• IgA proteases Destroy IgA antibodies
• Siderophores Take iron from host iron- binding proteins
• Alter surface proteins
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
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Endotoxin
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
•
• 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
Types of Exotoxins
Figure 15.5
Exotoxins
Exotoxin Lysogenic conversion
• Clostridium botulinum A-B toxin - Neurotoxin +
• Vibrio cholerae A-B toxin - Enterotoxin +
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Exotoxin
Source Mostly Gram positive
location Secreted by cell
Chemistry Protein
Fever? Type I (Superantigens)
Neutralized by antitoxin Yes
LD50Small
• 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 Fungi
• 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 Protozoa
• Presence of parasite may interfere with host function
• i.e. parasite clogs lymphatic vessels link
Pathogenic Properties of Helminths
Pathogenic Properties of Algae
• Neurotoxins produced by - Paralytic shellfish poisoning
• Respiratory tract
• Coughing, sneezing
• Gastrointestinal tract
• Feces, saliva
• Genitourinary tract
• Urine, vaginal secretions, semen
• Skin
• Skin infections
• Blood
• Biting arthropods, needles/syringes
Portals of Exit
Mechanisms of Pathogenicity