Pathogenicity Flashcards
Infection Cycle
the route an organism takes from one individual to another
horizontal transmission
from one member of a species to another
examples of contact transmission
direct, fomites, droplet
examples of vehicle transmission
water, food, air
examples of vector transmission
animals (ed, mosquitoes or ticks)
vertical transmission
from parent to child
accidental transmission
a host who is not part of the normal infectious cycle unintentionally encounters that cycle
Steps in pathogenicity:
- Exposure & portals of entry
- Adherence
- Penetration & evasion of host defense
- Damage to host cells (disease)
- Portals of exit (transmission)
3 Portals of entry:
mucous membranes, skin, parenteral route (penetration)
3 places you find mucous membranes
- Respiratory tract (common cold, influenza)
- Digestive tract (polio, cholera)
- Genitourinary tract
Skin is:
impenetrable to most organisms
Microbes get in through the skin by using:
hair follicles, sweat glands, and abrasions
What is the main symptom of tetanus?
paralysis
How do you get tetanus?
parenteral route
Pathogens use _______ __ ______ best suited to their mechanisms of pathogenesis.
portals of entry
Food-borne pathogens come through the:
mouth
The respiratory tract cathces:
airborne pathogens
What causes typhoid fever?
Salmonella typhi
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
ID50:
infectious dose for 50% of the test population
LD50:
lethal dose (of a toxin) for 50% of the test population
What is the ID50 (# of endospores) needed for B. anthracis to infect someone through the skin?
10-50 endospores
What is the ID50 (# of endospores) needed for B. anthracis to infect someone through inhalation?
10,000-20,000 endospores
What is the ID50 (# of endospores) needed for B. anthracis to infect someone through ingestion?
250,000-1,000,000 endospores
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:
- Glycocalyx: Streptococcus mutans
- Fimbriae: Escherichia coli
- 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?
- 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):
- using host nutrients (iron)
- causing damage at the site of invasion (cell lysis)
- Inducing hypersensitivity (allergy) reactions
- 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?
5
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:
- respiratory tract (coughing & sneezing)
- GI tract (feces & saliva)
- Genitourinary tract (urine & vaginal secretions)
- Skin
- Blood (arthropods that bite/needles/syringes)
