Pathogenicity Flashcards by Danica Wilson

Infection Cycle

the route an organism takes from one individual to another

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horizontal transmission

from one member of a species to another

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examples of contact transmission

direct, fomites, droplet

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examples of vehicle transmission

water, food, air

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examples of vector transmission

animals (ed, mosquitoes or ticks)

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vertical transmission

from parent to child

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accidental transmission

a host who is not part of the normal infectious cycle unintentionally encounters that cycle

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Steps in pathogenicity:

Exposure & portals of entry
Adherence
Penetration & evasion of host defense
Damage to host cells (disease)
Portals of exit (transmission)

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3 Portals of entry:

mucous membranes, skin, parenteral route (penetration)

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3 places you find mucous membranes

Respiratory tract (common cold, influenza)
Digestive tract (polio, cholera)
Genitourinary tract

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Skin is:

impenetrable to most organisms

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Microbes get in through the skin by using:

hair follicles, sweat glands, and abrasions

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What is the main symptom of tetanus?

paralysis

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How do you get tetanus?

parenteral route

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Pathogens use _______ __ ______ best suited to their mechanisms of pathogenesis.

portals of entry

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Food-borne pathogens come through the:

mouth

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The respiratory tract cathces:

airborne pathogens

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What causes typhoid fever?

Salmonella typhi

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What’s the difference between rubbing Salmonella typhi on the skin as opposed to ingesting it?

No reaction when rubbed on the skin but causes typhoid fever when swallowed

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ID50:

infectious dose for 50% of the test population

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LD50:

lethal dose (of a toxin) for 50% of the test population

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What is the ID50 (# of endospores) needed for B. anthracis to infect someone through the skin?

10-50 endospores

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What is the ID50 (# of endospores) needed for B. anthracis to infect someone through inhalation?

10,000-20,000 endospores

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What is the ID50 (# of endospores) needed for B. anthracis to infect someone through ingestion?

250,000-1,000,000 endospores

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What are the symptoms of gastrointestinal B. anthracis (rare)?

GI distress, vomiting of blood, diarrhea

What are the symptoms of pulmonary (inhaled) B. anthracis?

flu-like symptoms, then pneumonia

What are the symptoms of cutaneous B. anthracis (most common)?

skin lesions and necrotic ulcers

Adhesins/ligands bind to the _________ on host cells

receptors

3 examples of adhesins:

1. Glycocalyx: Streptococcus mutans 2. Fimbriae: Escherichia coli 3. M protein: S. pyrogenes

Microbes in ______ are sheltered from harmful factors (ex: antibiotics).

biofilms

What % of human infections are biofilms involved in?

65%

Invasins:

some microbes (eg. E. coli or Salmonella) produce protein (invasin) that alters host actin, causes membrane ruffling, microbe is engulfed.

How do capsules and cell wall components evade host defenses?

prevent phagocytosis

How do bacterial enzymes evade host defenses?

coagulases, kinases, hyaluronidase, & collagenase

What is another way pathogens evade host defense?

antigenic variation

3 species that prevent phagocytosis:

S. pneumoniae, H. influenzae, and B. anthracis

What protein resists digestion and where on the microbe is it produced?

M protein; produced on the cell surface and fimbriae

What species has the M protein?

S. pyrogenes (childbirth fever & sore throat)

What does mycolic acid do to evade host defenses?

resists digestion

What species has mycolic acid?

Mycobacterium tuberculosis

Fibrin and Clots can do what two things?

1. Isolate pathogens to prevent further infection | 2. protect some pathogens to hide from host cells

coagulases:

coagulates fibrinogen (forms blood clot in host)

kinases:

digest fibrin clots

hyaluronidases:

hydrolyze hyaluronic acid (breaks down extracellular matrix in host)

hyaluronic acid:

polysaccharide involved in holding cells together, particularly connective tissue

collagenase:

hydrolyzes collagen

collagen:

forms connective tissue of muscles

igA proteases:

destroy IgA antibodies

Antigenic variation:

many microbes can alter surgace antigens and evade host defenses

Antigenic drift

minor changes in capsid proteins caused by mutations that allow the virus to avoid the immune system

Antigenic shift

If two strains infect the host at the same time, the virsuses will recombine, giving each each virus a mix of the original viruses. This results in an immediate alteration of multiple genes.

Pathogens damage host cells by (4):

1. using host nutrients (iron) 2. causing damage at the site of invasion (cell lysis) 3. Inducing hypersensitivity (allergy) reactions 4. Producing toxins that can cause damage throughout the body

Toxins

poisonous substances produced by microbes

Toxincs can (4):

Inhibit protein synthesis destroy blood cells disrupt nervous system damage membranes

Some different symptoms toxins can cause:

fever, cardiovascular disturbances, shock, and diarrhea

exotoxins

released by bacteria, can act without growth of bacteria and/or distant from site of infection

cytolytic toxins

membrane-disrupting toxins that causes cell lysis

Cytolytic toxins work by either:

making protein channels in the plasma membrane OR disrupting the phospholipid bilayer

leukocidins

lyse white blood cells

hemolysins

lyse red blood cells

streptolysins

hemolysins produced by streptococci

An AB toxin is an __________ that consists of two subunits: the _ and _ subunits.

exotoxin; A & B

B subunit:

binds to the host cell to deliver the A subunit to the cytoplasm

How many B subunits are needed to form a pore for A entry?

A subunit:

has toxic activity

Many A subunits are:

ADP-ribosyltransferases

Botulinum toxin (C. botulinum)

is the most potent known biological toxin. It causes flaccid paralysis by binding to nerve cells and blocking the release of acetylcholine

Tetanus toxin (C. tetani)

Causes spastic paralysis by blocking glycine release from inhibitory interneuron

Cholera toxin (V. cholerae)

Causes secretion of electrolytes & fluids (diarhhea). Binds to epithelial cells.

Diptheria toxin (Corynebacterium diptheriae)

protein synthesis inhibitor

C. botulinum, C. tetani, V. cholerae, and C. diptheriae all have:

exotoxins

Endotoxins are produced by:

gram-negative bacteria ONLY

Endotoxins are in:

the lipopolysaccharide of the outer membrane

As bacteria die _____ _ is released, which causes a massive release of ________ from host cells. This can trigger fever, shock, and death.

Lipid A, cytokine

shock:

life threatening decrease in blood pressure

septic shock:

shock caused by bacteria

endotoxic shock:

shock caused by gram-negative bacteria

Endotoxins stimulate cytokine secretion by _________ --> __________ & leaky blood vessels --> _________ (low blood pressure) --> shock

macrophages; vasodilation; hypotension

5 portals of exit/transmission:

1. respiratory tract (coughing & sneezing) 2. GI tract (feces & saliva) 3. Genitourinary tract (urine & vaginal secretions) 4. Skin 5. Blood (arthropods that bite/needles/syringes)