Lecture 14 Flashcards
How do microorganisms enter a host?
- mucous membranes
- skin
- parenteral route (deposited directly into tissues when barriers are penetrated)
What is ID50?
infectious dose for 50% of a sample population
- measures virulence of microbe
What is the portal of entry and ID50 for bacillus anthracis?
skin: 10-50 endospores
inhalation: 10k-20k endospores
ingestion: 250k-1m
What is LD50?
lethal dose for 50% of a sample population
- measures potency of a toxin
What does lower LD50 values indicate?
higher toxicity or virulence
- takes a smaller dose to kill 50% of the population
What does a higher LD50 value indicate?
lower toxicity
- larger dose is required to kill 50% of the population
What is the LD50 of botulinum?
0.03 ng/kg
What is the LD50 of shiga toxin?
250 ng/kg
What is the LD50 of staphylococcal enterotoxin?
1350 ng/kg
What is adherence?
almost all pathogens attach to host tissues
What are adhesins?
ligands on the pathogen that bind to receptors on the host cells
- glycocalyx
- fimbriae
What do capsules do?
impairs phagocytosis
Give examples of bacteria and the diseases they lead to.
- streptococcus pneumoniae: pneumonia
- Haemophiles influenzae: pneumonia and meningitis
- bacillus anthracis: anthrax
- Yersinia pestis: plague
Where is glycocalyx found?
around the cell wall
What is in the cell wall? What are each of their functions?
- M protein resists phagocytosis
- Opa protein allows attachment to host cells
- Waxy lipid (mycolic acid) resists digestion
What does coagulase do?
coagulates fibrinogen
What do kinases do?
digests fibrin clots
What does hyaluronidase do?
digests polysaccharides that hold cells together
What does collagenase do?
breaks down collagen
What does IgA protease do?
destroys IgA antibodies
What is legionella pneumophila? How is it contracted?
- causes pneumonia
- infects lungs through inhalation (would not survive any other way of transmission)
What is bacillus anthracis? What are the ports of entry?
- causes anthrax
- skin, inhalation, ingestion
What are invasins? What do they cause?
- surface proteins produced by bacteria that rearrange actin filaments of the cytoskeleton
- cause membrane ruffling
What bacteria uses actin to move from one cell to the next?
shigella
listeria
How do bacteria survive inside phagocytes?
- low pH in phagolysosome
- escape from phagosome before lysosomal fusion
- prevention of fusion of lysosome with phagosome
How do biofilms help evade phagocytes?
- biofilm bacteria is more resistant to phagocytosis
- shielded by extracellular polymeric substance of biofilm
What nutrient is needed for most pathogenic bacteria?
iron
What are siderophores?
proteins secreted by pathogens that bind iron more tightly than host cells
What are examples of direct damage?
- disrupts host cell function
- uses host cell nutrients
- produces waste products
- multiplies in host cells and causes ruptures
What are toxins?
poisonous substances produced by microorganisms
What can toxins cause?
fever, cardiovascular problems, diarrhea, shock
What is toxigenicity?
ability of a microorganism to produce a toxin
What is toxiemia?
presence of toxin in the host’s blood
What is intoxication?
presence of toxin without microbial growth
What are exotoxins? What do they do?
proteins produced and secreted by bacteria
- soluble in bodily fluids
- destroys host cells
- inhibits metabolic functions
What are antitoxins?
antibodies against specific exotoxins
What are toxoids?
inactivated exotoxins used in vaccines
What do genotoxins damage? What does this cause?
damages DNA
- causes mutations
- disrupts cell division
- leads to cancer
Why do superantigens cause an intense immune response? What are symptoms they cause?
- release of cytokines from host cells (T cells)
- causes fever, nausea, vomiting, diarrhea, shock, death
What is each component on a A-B toxin?
A: enzyme
B: binding component
What do leukocidins do?
kill phagocytic leukocytes
What do hemolysins do?
kill erythrocytes by forming protein channels
What do streptolysins do?
same as hemolysins (kill erythrocytes by forming protein channels)
- just produced by streptococci instead
What are endotoxins?
portion of lipopolysaccharides of gram-negative bacteria (lipid)
When are endotoxins released? What do they do?
released during bacterial multiplication and when gram-negative bacteria die
- stimulate macrophages to release cytokines
- cause disseminated intravascular coagulation
What test is used for endotoxins?
limulus amebocyte lysate assay (LAL)
- horseshoe crab blood
How does the LAL assay work?
amebocytes lyse in the presence of endotoxins and produce a clot
What do plasmids carry?
genes for toxins, production of antibiotics and enzymes
What is lysogenic conversion?
changes characteristics of a microbe due to incorporation of a prophage
What are some examples of cytopathic effects?
- stopping cell synthesis
- causing cell lysosomes to release enzymes
- creating inclusion bodies in the cell cytoplasm
- fusing cells to create a syncytium
- changing host cell function or inducing chromosomal changes
- inducing antigenic changes on the cell surface
- loss of contact inhibition in the cell, leading to cancer
What are alpha and beta interferons produced by? What do they do?
produced by virally-infected cells
- protects neighboring cells from viral infection
- inhibits synthesis of viral proteins and host cell proteins
- kill virus-infected host cells by apoptosis
What is fungi? What can they cause?
toxic metabolic product
- can cause allergic response
What do trichothecene toxins do?
inhibit protein syntehsis
What do proteases do?
modify host cell membranes
What do capsules do?
prevents phagocytosis
What is ergot?
alkaloid toxin that causes hallucinations
What is aflatoxin?
carcinogenic toxin produced by aspergillus
What are mycotoxins?
produced by mushrooms and are neurotoxic
Give examples of mycotoxins.
Phalloidin
Amanitin
How do protozoa avoid host defenses?
- digesting cells and tissue fluids
- growing in phagocytes
- antigenic variation
What are helminths? What do they do?
parasitic worms
- use host tissue for growth
- produce large masses
- cause cellular damage
- produce waste products that cause symptoms
What neurotoxin can some algae produce?
saxitoxin
- paralytic shellfish poisoning
What are examples of portals of exit?
- respiratory tract (cough/sneeze)
- gastrointestinal tract (poop and spit)
- genitourinary tract (pee and cum)
- skin
- blood
