chapter 12: microbial pathogenicity
DESCRIPTION
Chapter 12: Microbial Pathogenicity. PathogenicityThe ability to cause disease VirulenceThe extent of pathogenicity. Portals of Entry. Mucous membranes Skin Parenteral route. Numbers of Invading Microbes. ID 50 : Infectious dose for 50% of the test population - PowerPoint PPT PresentationTRANSCRIPT
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
LD50 Small
• 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