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