Lecture 14 [Exam 4] Flashcards
What are the three types of defenses mammals have against disease-causing microbes?
Physical, chemical, and immunological defenses
What is the fundamental question of microbial pathogenesis?
How can an organism too small to be seen with the unaided eye kill a human a million times larger?
Who discovered that Bacillus anthracis causes anthrax?
Robert Koch
Define parasite.
An organism that receives benefits at the expense of a host. It refers to disease-causing protozoa and worms.
What are ectoparasites?
Parasites that live on the surface of the host.
Give an example of an ectoparasite.
Trichophyton rubrum, causes athlete’s foot
What are endoparasites?
Parasites that live inside the host’s body.
Give an example of an endoparasite.
Wuchereria bancrofti, causes elephantiasis
What does the term ‘infection’ imply?
A pathogen or parasite enters or begins to grow in or on a host.
What are primary pathogens?
Disease-causing microbes that can breach the defenses of healthy hosts.
Give an example of a primary pathogen.
Shigella flexneri, causes bacillary dysentery
What are opportunistic pathogens?
Pathogens that cause disease only in compromised hosts or unprotected sites.
Give an example of an opportunistic pathogen.
Pneumocystis jirovecii, causes pneumonia in AIDS patients
What is a latent infection?
An infection where microbes enter a dormant state and cannot be found by culture.
Give an example of a latent infection.
Herpesvirus, which remains dormant in peripheral nerves
Define pathogenicity.
An organism’s ability to cause disease.
What are the two components of pathogenicity?
- Infectivity
- Virulence
What does virulence measure?
The degree or severity of disease caused by a pathogen.
What is the lethal dose (LD50)?
The dose required to cause death in 50% of an experimental group of animal hosts.
What is the infectious dose (ID50)?
The dose required to cause disease, but not death, in 50% of an experimental group of animal hosts.
What is horizontal transmission?
Passage of infection from one person or animal to another. Can be occur through direct contact or indirect transmission.
What are fomites?
Inanimate objects that can transmit infectious agents.
Define vertical transmission.
Passage of infection from a mother to her fetus during pregnancy or birth.
What is a reservoir in the context of infection?
An environment or animal that harbors a pathogen.
What is an asymptomatic carrier?
A person who harbors a potential disease agent but has no symptoms.
List the portals of entry for infectious agents.
- Oral
- Respiratory tract
- Conjunctiva and mucous membranes
- Wounds, injuries, and skin lesions
- Parenteral route
What is immunopathogenesis?
The immune response to a pathogen that causes major tissue and organ damage. It is a calculated risk taken by the host to eradicate the pathogen making it a major contributor to pathology and disease.
What are virulence factors?
Factors employed by pathogens to enter a host, find a niche, avoid defenses, multiply, and transmit.
What are Molecular Koch’s postulates?
Criteria to confirm a suspected virulence gene’s role in pathogenicity.
What are pathogenicity islands?
Clusters of pathogenicity genes in the chromosome of bacterial pathogens.
What are pili?
Hairlike appendages that promote attachment of bacteria to host cells.
What are the two types of pili?
- Type I: adhere to carbohydrates
- Type IV: involved in twitching motility
What are exotoxins?
Proteins produced and secreted by bacteria that kill host cells and take their nutrients.
What are endotoxins?
Parts of lipopolysaccharide (LPS) of Gram-negative bacteria that hyperactivate host immune systems.
What are the two types of toxins based on the producing organism?
Exotoxins and endotoxins
What type of bacteria produce endotoxins?
Gram-negative bacteria
What is the size range of exotoxin proteins?
50 to 1,000 kDa
True or False: Exotoxins can be denatured by boiling.
True
What is the toxicity level of exotoxins?
High (1 microgram quantities)
What is the immunogenicity of exotoxins?
Highly antigenic
Endotoxins are poorly antigenic and are the primary cause of _______.
Gram-negative sepsis
List the nine categories of microbial exotoxins based on their mechanisms of action.
- Plasma membrane disruption
- Cytoskeleton alterations
- Protein synthesis disruption
- Cell cycle disruption
- Signal transduction disruption
- Disrupt cell-cell adherence
- Alter vesicular traffic
- Inhibit exocytosis
- Superantigens
What are the two types of exotoxins that disrupt host cell membranes?
- Pore-forming proteins
- Phospholipase
What is the function of hemolysins?
Lyse red blood cells
What type of toxin is produced by Staphylococcus aureus that forms pores in host cells?
Hemolytic alpha toxin
What is the structure of AB exotoxins?
Consist of 2 subunits, A and B
What role does the A subunit of AB exotoxins play?
Toxicity-associated factor
What is the mode of action of cholera toxin?
Increases cAMP levels, leading to watery stools
True or False: Vibrio cholerae invades host cells.
False
What are the two A subunits in anthrax toxin?
- Edema factor (EF)
- Lethal factor (LF)
What does the Shiga toxin target in host cells?
Disrupts protein synthesis by cleaving 28S rRNA
What disease is caused by diphtheria toxin?
Diphtheria
What is a microbe-associated molecular pattern (MAMP)?
Molecules that bind to Toll-like receptors
What symptoms can result from the release of endotoxins?
- Fever
- Activation of clotting factors
- Vasodilation
- Shock
- Death
What is a significant effect of sepsis-related endotoxin release?
Massive depletion of clotting factors
What are the types of secretion systems used by pathogens?
- Type I
- Type II
- Type III
- Type IV
What is the role of the type III secretion system (T3SS)?
Injects proteins directly into host cells
Type I pili are used for _______ attachment.
Static
How do intracellular pathogens avoid destruction?
Employ molecular tricks to misdirect the immune system
What distinguishes primary pathogens from opportunistic pathogens?
Primary pathogens cause disease in normal hosts; opportunistic pathogens require immunocompromised hosts
What are adhesins?
Molecules that mediate bacterial attachment to host cells
How many categories do exotoxins fall into based on their mechanisms of action?
Nine categories (*Plasma membrane disruption, *Protein synthesis disruption, *Signal transduction disruption)
What is a characteristic feature of two-subunit AB toxins?
They may use ADP-ribosylation to disrupt signaling processes or protein synthesis in the host
What type of bacteria produces endotoxin (LPS)?
Gram-negative bacteria
What are the three examples of protein secretion pathways used by pathogens to deliver toxins?
- Type II (pilus-like)
- Type III (syringe-like)
- Type IV (conjugation system-like)
What are molecular mechanisms bacteria use to avoid the immune system?
- Molecular mimicry
- Interfering with autophagy
- Redirecting ubiquitylation signals
What are intracellular pathogens capable of doing once inside the phagosome?
Escaping both innate and humoral host cell immune mechanisms
What are the three options for bacteria to avoid being killed by a phagolysosome?
- Grow inside the phagolysosome
- Prevent phagosome-lysosome fusion
- Escape the phagosome
What strategies do pathogens use to avoid extracellular immune factors?
- Production of a thick polysaccharide capsule
- Production of proteins that bind to antibodies
- Induction of apoptosis of phagocytic cells
- Alteration of surface antigens
_______________ refers to bacteria, virus, and fungi.
pathogens
True or False: Most infections go unnoticed.
True
True or False: Latent infections can emerge to suddenly cause cold sores.
True
_____________ is how easily an organism causes disease.
infectivity
True or False: The infectivity and virulence of a pathogen is shaped by the specific
genetic makeup of the pathogen.
True
___________ is highly virulent (50% fatality rate)
Ebola
_______ (cause of the common cold) are highly infective, but have a low virulence.
Rhinoviruses
________________ is the route of transmission of an infectious organism.
Infection cycle
In what three ways can transmission occur through arthropod vectors?
Transovarial, Accidental, or Mechanical transmission
A _______________ is an infection that normally affects animals but can be transmitted to human
Zoonotic disease
Give four examples of transmission vectors.
- through arthropod vectors (insect or
tick) feeding on animal reservoir hosts.
-. a mosquito vector (Aedes), transfers
yellow fever causing virus horizontally
from infected to uninfected individuals
when it feeds on a new host
-Infected insects involve vertical
transmission in the egg
-a host (not part of the normal infection
cycle) unintentionally encounters an
animal host-insect vector cycle
-a pathogen on the body surface of a vector
(ex. a fly after landing on fecal matter) is
transported to a susceptible host.
18
True or False: A reservoir is critically important for the survival of a pathogen and as a
source of infection.
True
__________ uses monkey as reservoir.
Yellow fever
_______________ uses birds as a reservoir.
The virus causing eastern equine encephalitis (EEE)
To fully understand any infectious disease study both ____________ and _____________.
pathogenic mechanisms, disease symptoms/immunopathogenesis
______________ is affected by pathogen’s growth and the host’s resulting immune response.
Host’s normal microbiome
True or False: Diarrhea reduces the overall numbers of gut microbiota.
True
True or False: Intestinal pathogens occupy host binding sites and alter
available nutrients.
True
To cause disease, all pathogens must:
- Enter a host
* 2. Find their unique niche
* 3. Avoid, circumvent, or subvert normal host defenses
* 4. Multiply
* 5. Transmit to a new susceptible host
Summarize Koch’s postulates.
- The phenotype under study should be associated with
pathogenic strains of a species. - Specific inactivation of the suspected virulence gene(s) should
lead to a measurable loss in virulence or pathogenicity. The
gene(s) should be isolated by molecular methods. - Reversion or replacement of the mutated gene should restore
pathogenicity.
Most pathogenicity islands are horizontally transmitted via ____________________.
conjugation or transduction
Some virulence genes reside on _________ or ___________.
plasmids or phage genomes
Pathogenicity islands may possess
several anomalies:
- Unique GC/AT ratio
- Linkage to a tRNA gene (integrase)
- Association with genes homologous
to phage/plasmid genes (movement from one organism to another)
Pili are composed of ____________.
pilinproteinsubunits
Tipscontain ___________ to attach to specific host cell receptors
receptors(FimH)
______________pili grow from outer membrane of certain Gram-negative bacteria and produce a static attachment to host cell
Type 1
____________ pili produce a dynamic attachment via assembly and disassembly
Grow from inner membrane of many Gram-negative bacteria.
Type IV
_______________ is the modelofpilus assembly anddisassembly that involves dozens of proteins.
Type IV pili
True or False: Type IV pili involve theelongationof the pili (attaches to asurface
the retractionofthepili ) and depolymerizesfromthebase,whichshortensthepilusandpullsthecell forward
True
True or False :Streptococcus pyogenes has the M protein which binds to host cell fibronectin (glycoprotein).
True
True or False: Bordetella pretussis has pertactin that binds to host cell integrin and also use pilus to bind to cells
True
True or False: Hostreceptorsdictatesusceptibilitytopathogens
True
True or False: Person-to-person differences in receptor structures are possible.
True
Individuals lacking ____________ are resistant to HIV infection.
CCR5
__________________ insert themselves into membranes by binding cholesterol and membrane receptors.
Pore-forming proteins
True or False: Panton-Valentine toxin of MRSA and Listeriolysin O of Listeria monocytogenes are pore-forming proteins (exotoxins).
True
________________ hydrolyze phospholipids into fatty acids
Phospholipase
True or False: Clostridium perfringens has phosplipidase C.
True
_______________ lyse white blood cells (leukocytes)
Leukocidins
True or False: Some exotoxins function as both hemolysins and leukocidins (e.x. Ex. Streptolysin S of Streptococcus pyogenes)
True
