Chapter 15 Flashcards
Q: Name the three portals of entry for pathogens.
A:
Mucous membranes: Respiratory tract, GI tract, GU tract, Conjunctiva
Skin
Parenteral route: Bites, cuts, Punctures, surgery, etc…
- most pathogens have a preferred portal of entry
Q: What do ID50 and LD50 represent?
A: Likelihood of causing disease increases as the number of pathogens increases.
ID50: Infectious dose for 50% of population; measures virulence of a microbe
LD50: Lethal dose for 50%; measures potency of a toxin
Q: Why is adherence important for pathogens?
A: It allows microbes to attach to host cells and establish infection, almost all pathogens attach to host tissues through adherence(adhesion)
Adhesins(ligands) on the pathogen bind to receptors on the host cells
-Streptococcus mutans - Glycocalyx adhesins
-E. Coli, Neisseria gonorrheoeae - Fimbriae w/ adhesins
- Streptococcus pyogenes - M protein
Q: What are biofilms, and why are they important?
A: Communities of microbes that share nutrients and attach to surfaces, can be several layers thick(containing several types of microbes), and can lead to infections in hospitals.
Q: Name the five virulence factors and their roles.
A: Capsules (evade immune system), cell wall components, enzymes, antigenic variation, host cell penetration.
Q: How can microorganisms damage a host?
A: Using up host nutrients, causing damage to host tissue in area of invasion, producing toxins that damage cells near and far from site of invasion, and inducing hypersensitivity reactions.
Q: What are portals of exit for microbes?
A:
Respiratory tract: Coughing and sneezing
Gastrointestinal tract: Feces and saliva
Genitourinary tract: Urine; secretions from the penis and vagina
Skin
Blood: Arthropods that bite; needles or syringes
Capsules
Glycocalyx around cell wall; prevents phagocytosis by preventing phagocytic cells from adhering
Cell Wall Components
M protein: Mediates attachment to cells and helps to resist phagocytosis
Fimbriae and Opa protein: Aids in attachment to host cells
Mycolic Acid(waxy lipid): Resists digestion after phagocytosis
Enzymes
Coagulase, Kinases, Hyaluronidase, Collagenase, IgA proteases
Antigenic Variation
Pathogens alter their surface antigens(and antibodies are rendered ineffective)
Penetration into the Host
Invasins, use actin to move from one cell to penetrate into the next
Exotoxins
Exotoxins are secreted proteins causing specific damage:
1. A-B toxins contain an enzyme component(A part) and a binding component(B part)
- Diphtheria toxin
- Genotoxins damage dna(Causing mutations, disrupting cell division, and leading to cancer)
2. Membrane disrupting Toxins: Lyse host cells by disrupting plasma membranes or to allow escape from phagosomes
- Leucocidins: Kill phagocytic leukocytes
- Hemolysis: Kills erythrocytes by forming protein channels
- Streptolysins: hemolysins produced by streptococci
* Disrupts phospholipid bilayer
3. Superantigens: Causes an intense immune response due to release of cytokines from host cells(T cells)
- Causes symptoms of fever, nausea, vomiting, diarrhea, shock and death
- Examples: Streptococcal toxins: food poisoning and toxic shock syndrome(ie; Botulinum Toxin)
Endotoxins
Endotoxins are cell wall components in Gram-negative bacteria that cause inflammation: Lipid A portion of lipopolysaccharides(LPS) of gram-negative bacteria; when lipid A is released during bacterial multiplication and when gram negative bacteria dies. This stimulates macrophages to release cytokines.
- Effects of endotoxin lipid A: Chills, fever, weakness, generalized aches, possibly shock and death, and can induce miscarriage.
* Disseminated intravascular coagulation: When small blood clots form, blocking capillaries providing blood to tissues.
- Tested for through LAL, Limulus amebocyte lysate assay.
Using up the hosts nutrients
- Iron is needed for growth of cells, including pathogens
- Siderophores: Proteins released by pathogen to gather iron molecules from cells
- Pathogens gather back siderophore receptors
