Exam 4 Micro Flashcards
Define pathogen
An organism that causes disease
Define commensal organisms
Bacteria that are normally found at various non-sterile body sites
Describe the human microbiome
The population (or consortium) of human-colonizing microbes
Name/identify the body sites that are most hospitable to bacteria and have their own microbiomes
?
Describe why skin is difficult for microbes to colonize
It’s dry, salty, acidic, or has protective oils
What is associated with acne?
Propionibacterium acnes
Describe factors that make the mouth hospitable to bacteria
- Lots of nutrients, food residue, epithelial debris, secretions
- Warm/moist
- Both gram + and gram -
What is associated with tooth decay?
Streptococcus mutans
Describe the mucociliary escalator in terms of its important components and its function and explain why it is important for lung function
Lining of trachea is covered with cilia that move to produce the escalator and sweeps foreign particles up and out of the lung
**we inhale microbes, we have to get rid of them
What is associated with stomach ulcers?
Helicobacter pylori
What location in the body has the most resident bacteria?
The intestine
Describe/identify factors that can influence the composition of the gut microbiota
- Your diet (most important)
- Chronic disease
- Sleep deprivation
- Stress
- Exercise
Define dysbiosis
An imbalance in the proportions of different commensal microbes in the gut
Define probiotics
Bacteria that are purposely ingested to promote a healthy gut microbiota
Describe fecal microbiotal transplants
A potential way to restore microbiotal populations
**Isolate healthy bacteria from fecal species and introduce it into a non-healthy species (dysbiosis) to try to restore health
Describe how scientists assess the composition of a microbiotal community (what method is most commonly used)
Extracting the DNA from a sample and subjecting it to 16s rDNA sequencing
Define opportunistic pathogen
An organism that typically only causes disease in an immunocompromised or already-sick individual
Distinguish among physical/chemical barriers, innate immune functions, and adaptive immune functions
- Physical/Chemical barriers: skin, mucous membranes, stomach
- Innate Immune functions: use specialized cells to detect and kill microbial invaders that get past the barriers
** Leukocytes (white blood cells), macrophages, cells expressing TLRs - Adaptive immune functions: recognizing antigens and epitopes
** Antibodies, cytotoxic T cells
Identify 3 physical barriers to microbes entering the body
- Skin
- Mucous membranes
- Stomach acid
Describe the functions of chemical barriers: lysozyme, peroxidase, iron-binding proteins, and defensins
- Lysozyme: degrades peptidogylcan
- Peroxidase: breaks down hydrogen peroxide into microbe damaging reactive oxygen
- Iron-binding proteins: bind iron so microbes can’t use it
- Defensins: small peptides that poke holes in microbial cell membranes
Describe pathogen-associated molecular patterns (PAMPs)
Patterns that could be associated with “suspicious” behavior (immune system might see it that way, as it’s the “police officer”)
**molecular patterns specifically associated with pathogens
Identify phagocytic cells that recognize and engulf pathogens to destroy them
- Neutrophils
- Monocytes (further differentiate into macrophages and dendritic cells)
Describe the process of phagocytosis and how it kills microbes – what is in the lysosome?
- Phagocytosis: immune cells engulf and destroy foreign particles
- Engulfed particle is held in phagosome –> then fuses with lysosome full of enzymes/toxins that destroy the microbe
**lysosome deposits microbe killing stuff into the phagosome
Describe pattern recognition (PRRs) in terms of their function and name 2 classes of PRRs
- Function: recognize PAMPS (signals the presence of foreign invaders or tissue damage) –> cells then sounds alarm
- Two classes: Toll-like receptors (TLRs) and NOD-like receptors
Describe the four cardinal signs of inflammation (not including loss of function)
- Heat
- Pain
- Redness
- Swelling
Define cytokine and describe common functions of cytokines
- Chemical signals
- Molecules that immune cells make to signal other cells
Describe the complement pathway from C3b to the membrane attack complex (MAC) in terms of what PAMP it senses and which bacteria are susceptible to damage by the MAC
- C3b protein of the complement pathway specifically recognizes LPS
- Membrane attack complex it stimulates is specific for gram negative bacterial cells
Distinguish between humoral immunity and cell-mediated immunity
- Hummoral immunity: involves antibodies (free floating proteins that recognize antigens, which are any foreign chemical structures)
**Antibodies bind to antigens –> stimulate other immune responses - Cell-mediated: uses T lympthocytes (T cells) that recognize antigens and destroy host cells that are infected
What are examples of adaptive immunity?
- B cells: mature in bone marrow
- T cells: mature in thymus
–help mediate different immune responses
Identify the primary and secondary lymphoid organs
- Primary: bone marrow and thymus
- Secondary: lymph nodes, tonsils and adenoids, spleen, Peyer’s patches (in small intestine), appendix
Define antigen and epitope
- Antigen: something that elicits and an adaptive immune response
- Epitope: the molecular pattern recognized by a given antibody
Describe the cellular interactions that permit massive antibody production to an antigen
B cell interacts with T cell that has seen the same antigen (T cell more or less gives B cell the go ahead) then B cell can differentiate into plasma cells
Describe the structure (light chains, heavy chains, variable and constant regions) and major functions of antibodies
- Heavy and light chains recognize specific molecular patterns
- Highly variable ends of the antibody fork – antibodies bind to antigens
- Carboxy termini contains constant region that other immune cells recognize
Describe the genetic process by which antibody diversity is generated form relatively few genes
Genetic recombination from relatively few genes but permitting many random combinations
Briefly describe how antibodies specifically interact with antigens/epitopes
Use the tips (variable regions) to have molecular interactions (basic chemistry)
Describe how B cells undergo negative selection to avoid autoimmunity
Any B cells that recognize self-antigens undergo negative selection, thereby destroying the antigens and preventing them from spreading
Distinguish between B cells and plasma cells with respect to antibody production
- B cell binding to a matching antigen triggers clonal expansion of that cell
- Plasma cells: cells that make large quantities of free floating antibodies
Describe memory B cells and their relationship to a secondary antibody response
Ready to make more antibodies if they encounter the same antigen in the future
Describe the function of antigen-presenting cells
Something that elicits and adaptive immune response
**doesn’t necessarily have to be something infective (just has to be foreign)
**present antigens to T cells
Define the function of the major histocompatibility complex (MHC) with respect to antigen presentation
- Antigens are presented on surface proteins called MHC
2.Pieces of foreign invaders are loaded onto MHC proteins for presentation to T cells
Describe the function of T cell receptors and what they interact with
Interact with antigens (only see antigens that are presented to them)
Describe how T cell receptor diversity is generated
Recombination process then hypermutation process
Distinguish between helper T cells and cytotoxic T cells with respect to their functions
- Helper: mediate different immune responses
- Cytotoxic: kill infected host cells
Describe how T cells are “educated” in the thymus to avoid autoimmunity
They’re educated so that they can effectively recognize antigens from invading pathogens but not react to components of our own
Describe the process by which cytotoxic T cells kill infected cells
The activated T(c) cell releases perforin to make holes in the membrane through which granzymes can enter to trigger cell death
Describe superantigens and why they can be dangerous
Antigens that can directly connect MCH and TCR molecules, causing massive T cell activation and cytokine release
**resulting massive immune response = extensive tissue damage
Describe how vaccines take advantage of adaptive immunity
Vaccines primarily cause humoral immune responses
–immunization = treated with one or more antigens together with an adjuvant, something that ellicits immune response –> once purified, killed, or deactivated, resulting memory B cells are ready to make the real antigen if the real pathogen comes later
Describe herd immunity
Immunization of most of a population is sufficient to dramatically reduce the spread of disease in that population
Define autoimmunity in terms of what the immune system recognizes or fails to recognize
Immune cells cannot distinguish between self-derived antigens and foreign antigens
Describe how molecular mimicry of the M protein of Streptococcus pyogenes can lead to rheumatic fever, an autoimmune disease
- M protein of S. pyogene has an epitope that mimics a cardiac antigen
- The epitope can be recognized by B cell and T cell, activating the B cell
- Resulting antibodies attack heart tissue = autoimmune disease
Define parasite and give examples of types of organisms that can be parasitic
- Parasite: bacteria, viruses, fungi, protozoa, and worms that colonize and harm their hosts
- Ex: protozoa and worms
Distinguish between endoparasite and ectoparasite
- Ecto: surface dwelling organisms
- Endo: organisms that live inside the body
Distinguish between primary pathogens and opportunistic pathogens
- Primary: cause disease in healthy hosts
- Opportunistic: cause disease only in immunocompromised hosts
Define pathogenicity
An organism’s ability to cause disease
Define virulence and relate it to LD50 or ID50 values (describe LD50 and ID50)
- Virulence: measure of the severity of a disease
- LD50 (lethal pathogen)
**how many bacteria are required to kill 1/2 of group - ID50 (non-lethal pathogen)
**how many organisms are required to cause disease symptoms in 1/2 of group
On the basis of infectious doses, accurately compare the virulence of two different pathogens
LOW LD50 = less organisms to kill host = more virulent
Define pathogen reservoir
An animal, bird, or insect that normally harbors the pathogen
Define a pathogen vector
In insect vectors, egg itself is infected during its formation
Define and distinguish among vertical, horizontal, and accidental pathogen transmission
- Vertical: transfer from parent to offspring
- Horizontal: individual to another
**directly or through food, fomites (inanimate objects), aerosols, or through a vector (like a bug) - Accidental transmission: when host that is not normally part of infection cycle encounters that cycle
Define immunopathogenesis
When the immune response to an infection damages host cells or tissues
Define virulence factor
Enhance the disease producing capacity (pathogenicity) of a pathogen
Describe the steps of pathogenesis once a pathogen enters the host body
- The pathogen must get in (portals of entry)
- The pathogen must make contact with host cells and attach to them
- The pathogen typically produces one or more toxins that help it survive and replicate while evading host immune mechanisms
- Pathogen must leave (often the same way it got in)
Describe the function of adhesins
Microbial factor that promotes attachment (grabs onto host cells)
Distinguish between type I and type IV pili with respect to the dynamics of their assembly
- Type I pili are static once assembled
- Type IV pili are dynamic, continually extending and contracting
Describe the mechanisms of bacterial exotoxins
- LPS released –> results in massive release of cytokines from host cells (sensed by TLRs)
- Cytokines trigger fever, shock, even death
Describe diphtheria toxin and cholera toxin (know the bacterial organisms that make these toxins and their targets in the host)
- Diphtheria toxin: targets protein synthesis in the host cell
**made by: Corynebacterium diphtheria - Cholera toxin: targets second messenger signaling in the host cell
**made by Vibrio cholerae
Describe bacterial endotoxins in terms of the class of bacteria that make them and where they are located
- LPS component of the outer membrane of gram negative bacteria
Describe type II secretion in terms of its mechanism/components and give an example of an organism that uses it
- Essentially rams protein out through an outer membrane pore structure
- Ex: Chlorera toxin
Describe type III secretion in terms of its mechanism/components and give an example of an organism that uses it
- Delivers specific proteins directly into the target host cells (via syringe like structure)
- Ex: Salmonella, Yersinia, Shigella
Describe type IV secretion in terms of its mechanism/components and give an example of an organism that uses it
- Like a mating pilus – used for conjugation but also modified to secrete proteins (+DNA)
- Can secrete from either cytoplasm or periplasm
- Ex: Bordetella pertussis
Define obligate intracellular pathogen and facultative intracellular pathogen
- Obligate: not known to grow or replicate outside of host cells
- Facultative: they can live inside or outside host cells
Identify phagosome escape, inhibition of phagosome-lysosome fusion, growth in the phagolysosome, and inhibition of antigen presentation as ways for microbial pathogens to escape destruction by the host immune system
- Phagosome escape: poke holes in phagosome membrane then leave
- Lysosome fusion: secretes toxins to interfere with lysosome signaling
3.
Define what makes a compound an antibiotic
Two essential characteristics:
1. Kills or stops bacteria growth
2. Does not harm eukaryotic cells/organisms
**BOTH must fit the criteria to be considered an antibiotic
Define spectrum of activity
- The breadth of activity that an antibiotic has
- Consists of a narrow (active against few species) and broad spectrum (active against MANY species)
Define a minimal inhibitory concentration (MIC) and be able to compare the potency of different antimicrobial compounds based on their MIC values
- MIC: lowest concentration of antibiotic that can still kill bacteria/stop their growth
- Lower MIC = more potent
Describe a Kirby-Bauer disk diffusion assay
Tests how sensitive a bacterial strain is to an antibiotic
What are targets for antibiotics?
- the cell wall
- the cell membrane
- DNA synthesis
- RNA synthesis
- protein synthesis
What is the target of B-lactam antibiotics?
The cell wall
What are some types of B-lactam antibiotics?
- Penicillins
- Cephalosporins
Distinguish between bactericidal and bacteriostatic antibiotics with respect to their effect on bacterial growth and survival
- Bactericidal: kills bacteria
- Bacteriostatic: stops growth of bacteria
What are examples of antibiotic resistance?
- Antibiotic destruction
- Antibiotic modification
- Antibiotic efflux
What’s an example of one mechanism of antibiotic resistance?
The modification of antibiotic targets
Explain how overuse of antibiotics relates to antibiotic selection and emergence of antibiotic-resistant pathogens
- Survival of the fittest – most resistant bacteria will survive
- Overuse permits selection in body
Define persister cells and distinguish persistence from resistance
- Persister cell: metabolically dormant, allowing it to survive antibiotic treatment
- Not genetically encoded
- Represent a random subpopulation of cells
Explain why fungal infections are often more difficult to treat than bacterial infections
- Fungi are eukaryotes similar to our cells
**antifungals risk being toxic to us as well - Fungi have a drug detox system that can inactivate many microbial agents
