Chapter 15: Microbial Mechanisms of Pathogenicity Flashcards
Pathogenicity:
The ability to cause disease.
Virulence:
The degree of pathogenicity. The ability of pathogen to cause disease, and how dangerous/deadly is.
Routes of microbial entry:
- Mucous membranes
- Skin
- Parenteral route
- Preferred portal of entry
- Mucous membrane:
a) Respiratory tract: nose/motuh; common cold, influenza.
b) Gastrointestinal tract: food/water, dirty fingers; cholera.
c) Genitourinary tract: sexually contracted; HIV.
d) Conjuctiva: eyelids/white of eyeballs; conjuntivitis.
- Skin:
Gain access through hair follicles and sweat glands.
- Parenteral route:
Deposited directly into tissues when barriers are penetrated. Ex: punctures, injections, bites, cuts = HIV, tetanus, gangrene.
- Preferred portal of entry:
- Cause infections through their specific portal of entry.
This is important because bacteria cannot survive in some regions of the body but can flourish in other.
Ex: Salmonella typhi, skin is not a good portal, prefers to be swallowed.
What type of action exposes microbes to each specific mucous membrane?
ID50
Infectious Dose for 50% of sample population.
Measures the virulence of a microbe.
LD50
Lethal Dose for 50% of sample population.
Measures potency of a toxin.
How do capsules help bacteria evade the immune system?
Prevents phagocytic cell from adhering to the bacterium.
- Capsule= virulent (makes it ‘slippery’ to immune system)
- No capsule= avirulent (still infected but won’t cause disease)
Enzymes that facilitate microbial colonization of the human body:
Enzymes are often secreted by the invading organism (bacteria).
a) Coagulases
b) Kinases
c) Hyaluronidase
d) Collagenase
e) IgA protease
a) Coagulases:
Clots blood and forms a barrier to protect from phagocytosis (immune cells) and other body defenses
b) Kinases:
Breaks down blood clots formed, to get released in bloodstream and infect more.
c) Hyaluronidase:
Holds together connective tissue; (Contributes to pathogenicity by helping organism spread. (gangrene)
d) Collagenase:
Helps break down collagen from tissue; facilitates spread of gangrene.
e) IgA protease:
Destroys IgA antibodies (mucus membranes)
(Contributes to pathogenicity by inhibiting immune response)
Ways bacteria can damage host’s cells:
- Using hosts nutrients
- Causing direct damage in the immediate vicinity of the invasion.
- Producing toxins transported by blood and lymph, that damage sites far removed.
Hemolysin:
Membrane disrupting toxins that lyses open red blood cells (erythrocytes), by forming protein channels.
Kills RBC to better outcompete for iron nutrients; helps invade host and lyse of RBC gives iron to pathogens.
(Contributes to pathogenicity by supplying nutrients for growth)
Siderophore:
Proteins secreted by pathogens that bind iron more tightly that host cells (contributes to pathogenicity by steal/taking iron from us)
Endotoxin:
Toxins that are part of the bacterial cell ( not a product )
Lipid A is the ONLY endotoxin. They are only found in (the outer wall) Gram-Negative bacteria.
Exotoxin:
Toxins secreted from the bacterial cell (product release outside).
Can be found in Gram positive(mostly) and negative.
Types of Exotoxins:
A) Type l: Superantigens.
B) Type ll: Membrane-disrupting toxins.
C) Type lll: A-B toxins
A) Type l: Superantigens
cause an immune response due to release of cytokines from host cells.
Symptoms of fever, nausea, vomiting, diarrhea and death.
