8-2: Microbial Pathogenesis Flashcards
Which domain of life lacks pathogenic organisms?
Archaea! (or at least, we don’t know any yet)
What are phytopathogens?
Microbial pathogens that target plants. Eg. Erwinia amylovora which targets apples.
What are more common than bacterial pathogens targeting plants?
Fungal pathogens, eg. fusarium oxysporum, causing Panama disease in the Gros Michel bana
What is Dutch Elm Disease>
Fungal pathogen carried by bark beetles from asia.
What is an infection
Invasion of body by a disease-causing organism. Can result in disease, but not the same thing as disease.
What is a disease
Damage or injury to host organism. Some bacteria cause disease without infection (using toxins).
What is a pathogen
An organism that causes disease
What is pathogenesis
Mechanism that leads to disease
What is virulence
Similar to pathogenesis, used to describe the severity of the disease. Eg. “highly virulent”
What is an opportunistic pathogen
Organism that is often non-pathogenic, but becomes pathogen under certain circumstances
What are symptoms of a bacterial disease are caused by?
Activities of pathogen (eg. toxins, tissue damage) or immune response to pathogens (fever, rashes, redness, swelling)
What are the 4 major steps in many infections/microbial diseases?
Adherence: binding to specific host cells/tissues
Colonization: expanding population (planktonic or biofilm)
Invasion: gain access to privileged sites through mucous membranes
Spread: move beyond site of initial infection
What is a mucous membrane
Tightly packed epithelial cell layers covered with a protective mucous layer. Lines body access points (airways, oral cavity and GI).
What is invasion
Ability of pathogen to enter host cells and/or tissues. Penetrate beyond where microbes usually reside
Strategies of invasion
Entering host cells, damaging epithelial layers
How does S. pyogenes invade cells?
Secreting enzyme called hyluranidase that degrades hyluronic acid, disrupting the epithelial layer.
What is a virulence factor
Molecules produced by a pathogen that contribute to its ability to cause disease
What are some common types of virulence factors? (5)
- Adhesion factors
- Nutrient acquisition (eg. iron sideophores)
- Immune resistance (resistance to ROS)
- Immune evasion/disruption (hide from immune system)
- Extracellular enzymes, protein secretion systems/effectors and toxins (damage host)
Describe adherence as a virulence factor
Microbes typically target specific cell or tissue type by adhering to specific receptors on those cells.
Provides foothold, facilitates interaction/invasion of host cells
What are some examples of adherence factors? (adhesins)
Pili, fimbriae, surface proteins, capsules
What are some common adherence receptors?
Glycoprotein, glycolipids
How do pathogens evade the immune system
Hide inside cells
Produce capsule to hide surface antigens
Modify antigens e.g. pathogen associated molecular patterns (PAMPs) like LPS that are detected by immune system
How do extracellular enzymes promote virulence
Free up nutrients, damage host cells, inactivate immune cell mechanisms, disrupt barriers to enable invasion
Give two examples of extracellular enzymes.
S. aureus and coagulase, S. pyogenes and streptokinase
What is the major secretion system is used by virulent pathogens?
Type III secretion system (T3SS), which is similar to T6SS
How do T3SS work?
Inject effector proteins into host cells. Effectors have specific target to manipulate host cell biology, like inactivating signalling proteins.
Aside from T3SS, what secretion system do other pathogens use?
Type IV secretion system, like L. pneumophila.
What are exotoxins?
Secreted protein toxins, similar to bacteriocins, but target the host.
Give an example of a bacterial toxin
Alpha-toxin from S. aureus. Proteins polymerize to form a pore.
What are AB-type toxins
Subunit A exerts biological effect (modify/degrade specific molecules), Subunit B binds host cell glycoprotein/lipid to mediate uptake
What are the two types of AB toxins?
AB and AB5
Give an example of AB type toxin.
Botulinum toxin produced by clostridium botulinum.
What does the A subunit do of botulinum toxin do? What does the B subunit do?
A subunit: protease that cleaves SNARE protens needed to release ACh
B subunit: targets motor neurons
Botulinum toxin leads to what condition?
Muscle paralysis
How are toxins used as therapeutics?
Inactivated toxins as vaccines
Treat non-bacterial diseases
Botox (botulinum toxin) = helps migraines, cerebral palsy
How are toxins and secretion systems effector proteins different?
Toxins are more potent and diffuse/spread to distant cells.
SS effectors need direct contact with the cell and often work together.
What causes the plague?
Yersinia pestis, a Gram negative proteobacterium.
How does one aquire the plague?
Fleas, the disease vector, spread disease between rodents. Fleas bite people in the absence of rodents.
What are the three types of plague?
Bubonic (lymph nodes), pneumonic (lungs), septicemic (bloodstream)
What organism did Yersinia pestis evolve from?
Yersinia pseudotuberculosis, via several virulence adaptations that allowed it to hide from the immune system.
What are some factors that allow Yersinia pestis to survive in fleas?
Yersinia murine roxin, a phospholipase D that appears to detoxikfy an unknown substance in flea guts.
What is the main virulence of Yersinia pestis caused by?
T3SS injects effector proteins into immune cells
F1 capsule inhibits uptake of Y pestis by immune system, inhibits surface antigen detection
