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158 Cards in this Set
- Front
- Back
What is microbial pathogenesis?
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Development of a disease and the events of that disease caused by a microbial agent [bacteria, virus, protozoan, fungi]
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What contributed to the reduction of mortality during the 20th century?
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•Improved sanitation
•Effective vaccine development •Antibiotics •Effective quarantine measures |
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What is an emerging infectious disease?
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•New [never seen before] disease that appears in nature; often due to increased human contact with microbe that has been around for years
•Cause has only recently been identified |
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What is a reemerging infectious disease?
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Infectious disease that was previously under control or eliminated
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What are the 4 categories of emerging and reemerging infections?
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1. New-New
2. New-Old 3. Old-New 4. Old-Old |
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What is a New-New disease?
List an example |
Disease caused by previously unidentified bacteria that have recently entered the population
•Lyme Disease oBorrelia burgdorferi oVector: Deer Tick •Legionnaire’s Disease oLegionella pneumophila oAirborne transmission oFound in soil & water |
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What is a New-Old disease?
List an example |
Disease caused by newly recognized pathogens that have been around a long time
•Food borne Diseases by: oCampylobacter jejuni oCampylobacter coli •Cat Scratch Fever [WWII Trench Fever] oBartonella henselae oVector: Flea infested cats |
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What is an Old-New disease?
List an example |
Disease caused by well known pathogens thought to have been eliminated but have recently reappeared
•Tuberculosis oMycobacterium tuberculosis •Cholera oVibrio cholera |
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What is an Old-Old disease?
List an example |
Disease caused by long known bacteria which are only recently being noticed by the public that remains in high incidence
•Chlamydia oChlamydia trachomatis •Gonorrhea oNeisseria gonorrhoeae |
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What is bioterrorism?
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•The use of microbes or toxins to disrupt normal societal functions
•Biological/germ warfare |
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What are the major forms of bioterrorism?
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1.Deliberate poisoning of food/water with infectious material
2.Use of microorganisms or animals, toxins, living or dead in a weapon system 3.Use of biologically inoculated fabric |
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What are the 3 main categories of bioterrorism agents?
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1. Category A
2. Category B 3. Category C |
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Why is prevention and surveillance important?
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•Increase vaccinations, public awareness of disease & resistance, & advanced antibiotics
•Surveilance for effective action •Improve public health |
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Describe Category A bioterrorism agents
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•High priority agents that pose risk to national security
•Easily transmitted & spread •High mortality rates |
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Describe Category B bioterrorism agents
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•2nd highest priority agents
•Moderately easy to spread •Low mortality/Medium morbidity |
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Describe Category C bioterrorism agents
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•3rd highest priority disease
•Emerging pathogens that could become engineered in the future •Agent easily procured •Easily spread •Potential for high mortality/morbidity |
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How are infectious diseases appearing and why?
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•Antibiotic resistant strains, emerging infectious diseases, and bioterrorism
•Emergence of new pathogens, spread of resistant organisms, medical progress that predisposes to infection, and realization of engineered biological weapons |
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What is an opportunistic pathogen?
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Organism that normally would not cause human infection
•Can be due to a weakened immune system or accidental ingestion of a microbe •Immunosuppression for treatment or immune response to surgery/transplant |
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What is a microbial shift disease?
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A shift in the population of microbes that normally resides at a particular site, resulting in disease at that site
•Bacterial vaginosis oShift of normal flora of Gram (+) bacteria to Gram (-) |
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How has genomics played a role in microbial research advancement?
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DNA sequencing technology
•Sequencing of microbial genomes has enabled researchers to understand virulence and pathogenicity |
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What traits make a bacterium more dangerous?
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•Antibiotic resistance
•Toxicity |
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How can we reduce nosocomial infections?
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•Improve hygienic practices
•Decrease dependence/overuse of antibiotics •Dedicated infection control officers |
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What are some bacterial infections?
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•Ulcers
•Heart disease •Alzheimer’s Can be treated by antimicrobial agents and prevented by vaccination |
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Who was Robert Koch and what was his contribution to science?
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Robert Koch was a German microbiologist who developed Koch’s Postulates, a tool for proving a disease is caused by a bacterium using scientific methods
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What are Koch’s 4 postulates?
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1.Microbe must be associated with the lesions of the disease
2.Microbe must be isolated from the lesions of the disease in pure culture 3.Pure culture of the microbe should cause the symptoms of the disease if it is inoculated into humans or animals 4.Microbe must be re-isolated in pure culture from the humans or animals used to satisfy the 3rd postulate |
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What are problems with Koch’s postulates?
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1.some bacteria are asymptomatic
2.some bacteria cannot be cultivated 3.ethics involved with human inoculation and no “perfect” animal comparison 4.Koch’s Postulates do not work for microbial shift diseases |
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What is a possible 5th postulate?
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Information about the microbe should enable scientists to design effective therapeutic or preventative measures
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What is a normal flora?
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A collective of bacteria or microorganisms within a host or a specific location within the host
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Describe the problem of Koch’s postulates with microbiota shift diseases
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•It is difficult to satisfy distinguish one microbe as causing the disease
•Disease might be an effect of microbial interactions |
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How is a pathogen proven to be clinically significant or the cause of a particular disease [Koch]?
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•Microbe is isolated in abundance
•It is isolated in pure culture •It is isolated on more than one occasion •Can be isolated from deep tissues •Evidence that the microbe causes inflammation •Evidence of immune response to pathogen •Fits with clinical picture |
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Describe some host-microbe interaction in relation to disease
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•Some disease causing bacteria evolved specifically to be pathogenic to humans
•Some are never part of normal flora; humans are accidental hosts •Some bacteria in normal flora are pathogenic outside their niche •Immunocompromised patients become “prey” to opportunists |
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Define contamination
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The presence of microbes
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Define infection
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Successful colonization of the body by a microorganism capable of causing damage to the body [can be asymptomatic]
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Define disease
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An infection that causes symptoms; an abnormal and harmful condition of bodily function(s) or structure
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Define colonization
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The attachment and multiplication of a bacterium [within a particular site]
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Define [overt/clinical] sign
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Observable characteristic of a disease [upon examination]
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Define [subclinical] symptom
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•Observation of a disease that is apparent only to patient
•Only patient can feel effects of bacterial colonization |
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Define syndrome
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Combination of signs & symptoms that characterize a specific disease
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Define pathogen
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Organism capable of causing disease
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Define pathogenicity
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Capacity/ability of an organism to cause disease/harm
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Define virulence factor [mechanism]
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Bacterial product/strategy that contributes to the ability of the bacterium to cause infection
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What is resident microflora?
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Microbes that are always present in/on human body
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What is transient microflora?
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Microorganisms that can be present under certain conditions anywhere resident microflora are found
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What are the different models used to measure infectivity and virulence and what are their benefits/limits?
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1.Animal models
a.Cheap & low maintenance b.Similar anatomy, but not perfect c.Genetically manipulated d.Different effects of microbes 2.Humans a.Best model, but ethical issues exist |
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What are ID50 and LD50?
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•ID50: dosage of bacteria necessary to infect 50% of animals exposed to bacterium
•LD50: dosage of bacteria lethal to 50% of animals exposed to bacterium |
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What are the limitations of ID50 & LD50?
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•Crude measures
•Lack of sensitivity •Lack of infection •Lack of mortality •Cannot compare 2 different diseases |
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What is a competition assay?
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Mixing wild-type and mutant strains together to inoculate an animal, and compare the numbers of each retrieved from animal
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What are the pros and cons of using organ cultures?
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What are the pros and cons of using tissue cultures?
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What is Molecular Koch’s Postulates?
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Set of experimental criteria that must be satisfied to show a gene or set of genes in a pathogenic microorganism codes for a product contributing to virulence [often referred to as virulence factors]
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Briefly describe Molecular Koch’s Postulates
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1.Identify genes/genes responsible for virulence [Present in strains that cause disease, not avirulent strains]
2.Gene disruption reduces virulence 3.Introduction of gene into avirulent strain causes virulence 4.Gene causing virulence is expressed during infection 5.Specific immune response to gene protects against disease |
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Where are most known bacterial genome sequences available for comparison?
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Databases such as:
• NCBI • TIGR • Sanger Institute |
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How can Molecular Koch's Postulates be used to understand bacterial pathogenesis?
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It provides a way to prove that a gene or set of genes cause virulence within a microorganism; knowing this provides a base to understanding pathogenicity
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List the various molecular diagnostic methods
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•Polymerase Chain Reaction [PCR]
•Checkerboard Hybridization •Rapid-PCR •Ligase Chain Reaction [LCR] •Ribotyping using RFLP •PFGE Analysis |
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Describe Polymerase Chain Reaction
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•Use primers specific for conserved regions of rRNA genes
•Amplify region and sequence •Compare to available databases •Ideal for organisms that can’t be cultivated •Reagents required for PCR: oDNA, Primers, Nucleotides, Taq DNA Polymerase, +MgCl & Buffer |
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Describe Checkerboard Hybridization
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•Probes are applied in lines to membrane filter
•Labeled amplicons of rRNA genes are applied perpendicularly to probes •DNA bound to probe appears as black spot •Indicative of presence of organism |
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Describe Rapid-PCR
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•Random-primed PCR
•Rather than using specific primers, random primers bind to many different sites on genome •Produces a mixture of differently sized amplicons •Able to distinguish between bacterial species through pattern differences |
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Describe Ligase Chain Reaction
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•2 specific primers [one labeled] hybridize to sequences adjacent to each other
•Successive rounds of Denaturation, Renaturation, & DNA Ligase •Primer pairs increase in concentration if they bind tightly enough to target DNA •More sensitive than serology |
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Describe Ribotyping/RFLP
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•A lot of DNA is required
•DNA is digested with restriction enzyme •Fragments separated by electrophoresis and transferred to membrane •Hybridized to probe for rRNA genes •Compare banding pattern to differentiate between strains and species •Used to track M. tuberculosis |
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Describe PFGE
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•Pulsed Field Gel Electrophoresis
•DNA incubated with restriction enzyme that cuts only in a few spots •Electrophoresed and pulse direction is switched periodically •DNA separated based on size •Used in outbreaks to trace strain origin |
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What are the benefits of molecular diagnostics over cultivation techniques?
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•Rapid results
•Cost effective •Sensitivity •No need to cultivate organisms |
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What are some benefits and problems with using genome sequencing?
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•Sequences are linked to specific functions
•A gene can be tested for proposed functions •There are genes that have unidentified or misidentified functions •1/3 of genes are not recognized •Identification is questionable •Gene for known proteins unrecognized in databases |
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What do microarrays provide?
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•Determination of gene function
•Growth under various conditions [i.e. low iron] compared to normal growth conditions •Comparison can help identify gene function |
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Define a microarray
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Chips that contain DNA segments representing all the genes in the genome
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With the advancement and benefits of molecular methods in diagnosis, why are many laboratories still practicing cultivation techniques?
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• Technicians lack training in molecular biology techniques
• Technicians are familiar with cultivation techniques •Fear of irreproducibility and lawsuits |
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What was the traditional means of molecular diagnosis?
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Cultivation on growth media followed by various chemical tests
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What is an important application of the Ligase Chain Reaction technique?
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Detection of chlamydial disease caused by Chlamydia trachomatis
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What are the various methods for identifying virulence factors?
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•Cloning
•Transposon Mutagenesis •Transcriptional Fusions •In Vivo [Gene] Expression Technology Signature-tagged Mutagenesis |
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What is the problem with using in vitro techniques in studying virulence?
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In vitro analyses cannot mimic in vivo experiments
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Describe cloning
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•Gene mining for genes of interest [in virulent type]
•Clone genes of interest from pathogen into avirulent strain •Check for change in virulence [of avirulent strain] |
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Describe transposon mutagenesis
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•Make random mutations in the pathogen by introducing transposon(s)
•Transposon usually carry a selectable marker/reporter gene •Generation of mutant library •Shows effects of random knockouts |
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Describe transcriptional fusions
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•Identification of potential virulence genes by their regulatory properties
•Screen genome for genes similar to virulence genes in other organisms or itself o Check for similar manners of regulation o Link the promoter/operator region to reporter gene o Analyze reporter gene |
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Describe in vivo expression technology [IVET]
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•Used to detect genes essential for bacterial survival
•Use purA as reporter [lacks promoter] •Purine biosynthesis •Look for genes that are not expressed in vitro |
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Describe signature-tagged mutagenesis
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•In vivo form of transposon mutagenesis; a negative selection method
•Mutant library formed from incorporation of tagged transposons into bacterial strain, and mixture is injected into animal •Recover virulent [those that survived] bacteria and compare to original to see which ones died •Look for original mutants that do not hybridize •Retrieve original of lost mutants and examine for loss of virulence |
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What are the factors contributing to an organism’s virulence on the molecular level?
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•Bacterial toxins [proteins that damage host cells
•Ability to adhere to tissue •Ability to forcefully be consumed by non-phagocytic cells |
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What are some limitations to cloning?
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Cloning only focuses on a short portion of the genome, so there is a possibility that there are more genes outside that portion adding to the phenotype [virulence factor], and this technique requires an avirulent strain
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What is a transposon?
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DNA segments that integrate randomly
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What the limitations to transposon mutagenesis?
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•Could knockout function of downstream [linked] genes
•Can only identify non-essential [non-vital] genes |
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Differentiate between specific and non-specific defenses
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•Non-specific/Innate: defenses do not distinguish one infectious microbe from another
•Specific/Adaptive/Active: defenses recognize and defend against antigen by producing antibodies and activating lymphocytes |
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What are similarities between specific & non-specific defenses?
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•Both types interact with each other
•Controlled and organized by cytokine and chemokine •Antibodies help phagocytes ingest and kill bacteria •Antibodies can activate complement •Both can go out of control |
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What is a cytokine?
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Signaling protein
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What is a chemokine?
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Protein produced by many human cells that organizes cell defense activities
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What happens in an out of control non-specific defense?
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Septic shock
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What happens in an out of control specific defense?
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Autoimmune disease
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What are some non-specific defenses?
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•Physical/Chemical barriers
•Cellular/Molecular defenses •Inflammation •Fever |
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Draw and label an antibody
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Define & describe the epithelium
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A cellular surface lining layer
On outer surfaces, cells are bound tightly together to prevent intercellular movement of bacteria, but endothelial cells [associated with the cardiovascular system] are not tightly bound to allow movement of phagocytic cells [which also allows bacterial movement] |
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What are some of the protection systems within the epithelia?
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•Mucous
•Defensins •Toxic lipids •Lysozyme |
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What are the physical barriers?
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•Skin: protects body from injury
•Mucous membranes: make it difficult for invasion and flushes system |
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How can bacteria enter through the skin?
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Either through a breech in the skin or through vector transmission
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What are the layers of skin?
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Epidermis
Dermis |
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Describe the epidermis
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•Stratified squamous cells
•Keratinocytes •Unfavorable microbial environment o Dry, acidic, salty, Sebum, low temperature, competition with resident flora, UV |
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Describe the dermis
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•Connective tissue layer
•Location of glands and follicles |
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What is a polarized cell?
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A cell oriented with a basolateral and apical surface
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What is Sebum?
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Oily matter secreted by Sebaceous glands in the skin
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Describe the normal flora of the skin
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•Primarily Gram (+) cocci and bacilli
•Fights foreign pathogens by competing for space/binding sites and nutrition •Secrete antimicrobial chemicals |
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How might the normal flora of the body harm it?
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•Some are opportunistic and cause harm to the body if they are introduced to an area other than their normal site, either by wound or medical device
•Can be problematic for treatment due to antibiotic resistance |
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Why are simple epithelia more vulnerable to bacterial invasion than stratified epithelia?
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Invading bacteria only have to pass through one layer of cells to gain access to underlying tissue
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Describe the defenses of the dermis should pathogens breech the epidermis
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•Langerhans cells [dendritic cells] process antigen and activate specific defenses
•Skin Associated Lymphoid Tissue [SALT]: skins personal defense system |
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Which epithelial surfaces are ideal for bacteria and why?
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•Respiratory, gastrointestinal and urogenital tracts
Ideal due to optimal pH, temperature and moisture |
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Describe mucus
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•Produced by goblet cells
•Contains a mixture of glycoproteins •Contains antibacterial proteins o Lysozyme, Lactoferrin, Defensins •Production of immunoglobulin sIgA |
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Describe the normal flora of mucus
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Gram (+) and (-) bacteria found on nearly all mucosal epithelia except the uterus, upper female genital tract and upper urinary tract
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What is MALT and GALT?
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•MALT: Mucosa Associated Lymphoid Tissue
•GALT: Gastrointestinal Associated Lymphoid Tissue Specific defenses composed of Macrophages, B & T cells and produces sIgA |
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Where is GALT found?
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Follicles and Peyer's patches of intestinal epithelium
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What are non-specific cellular defenses?
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Phagocytes & Non-Specific Cytotoxic Cells
oPhagocytes: PMNs, Monocytes, Macrophages: Ingest and kill bacteria •Natural Killer Cells: Attack infected human cells |
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What is a granulocyte and what are the different types?
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Cell with granules in cytoplasm and an irregular, lobed nucleus derived from bone marrow
•Basophils [histamine/inflammation] •Eosinophils •Neutrophils |
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What is a agranulocyte and what are the different types?
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Cells that lack granules in cytoplasm & have a round nucleus
• Monocytes • Lymphocytes |
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Describe monocytes
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•An agranulocyte that differentiates into macrophages [Rapid during infection]
•Antigen causes monocytes to release cytokines which stimulates phagocytic cell activity |
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What are the types of macrophages?
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•Free
o Amoebocytic: can leave circulatory system and enter tissue o Found in most tissues •Stationary o Do not move o Found in organs that filter lymph or blood |
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Describe phagocytes
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•Cells that eat/engulf foreign materials, dead cells and debris
•Guards skin and mucus membranes •Not capable of cell division |
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Describe phagocytosis
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Neutrophil and Macrophage 4 steps
• Find • Adhere • Ingest • Digest |
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What is transmigration?
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When the cells of the immune system move from the blood vessels through the walls to tissue
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What is chemotaxis?
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Movement of a cell [host or bacteria] towards a particular substance/stimulus
• Phagocytes attracted to chemicals released by infectious agents, damaged tissue and cytokines |
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What is lymph?
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Fluid that moves through the lymphatic system that is monitored and sterilized by phagocytes
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What are the 3 major functions of the lymphatic system?
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•Collects excess fluid from the spaces between body cells
•Transports digested fats to the cardiovascular system •Provides many of the specific and non-specific defense mechanisms against infection and disease |
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Where does the process of draining excess fluid from the spaces between cells begin?
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Lymphatic capillaries
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Describe phagocyte adherence
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•Phagocyte binds to microbe [difficult if microbe is capsulated]
oOvercome by complement or antibodies •Once adhered, microbe engulfed [phagosome] |
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Describe phagocyte digestion
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Digested by lysosomes within cytoplasm[contain digestive enzymes and defensins]
•Fusion forming phagolysosome •Myeloperoxidase •Inactivate essential bacterial proteins |
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What is a defensin?
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Small lysosomal peptides that kill bacteria
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What triggers polymorphonuclear leukocytes to leave blood?
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• Complement
• Cytokines • Chemokines |
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What is a dendritic cell?
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•Cell that trigger specific immune responses in many tissues
•Examples: o Langerhans cells o Kupffer cells o Alveolar macrophages o Spleen macrophages o Dendritic cells of lymph nodes |
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What is a mast cell?
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•Cells that congregate around blood vessels and detect foreign matter
•They release granules containing histamine resulting in vasodilation [helps PMN’s to move to infection site] |
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What does the flow of lymph depend on?
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Skeletal muscle contractions
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Describe lymph nodes
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•Cleans lymph for return to blood
•Traps and destroys materials in lymph |
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What are the functions of complement?
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•Enhance phagocytosis through opsonization
•Lyse microorganisms •Generate peptide fragments that regulate inflammation and immune responses |
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What are the complement pathways?
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• Alternative pathway
• Classical pathway • Lectin [Mannose binding] pathway |
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What is complement activation?
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Alteration of complement proteins such that they interact with the next component [cascade]
•Classical: collectins & antibodies attach to mannose on bacteria •Alternative: complement components bind to bacteria |
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What is complement fixation?
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Fixing/consuming of complement by antigen-antibody complexes
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How do the pathways differ?
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They differ in the steps that initiate formation of C3 convertase
• Classical: C1qrs -> C2 & C4 • Lectin: MBL -> activation of C2 & C4 • Alternative: interaction between microbial surface and C3 |
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What is the final product of complement activation?
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Membrane Attack Complexes [MAC]
Produces transmembrane channels in Gram- negative bacteria |
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What does C3b do?
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•Triggers MAC
•Binds to complement receptors on phagocytes •Opsonization of pathogens •Removal of immune complexes |
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What stimulates chemotaxis and enhances inflammatory effect?
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• C3a
• C4a • C5a |
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Which factors are involved in alternative pathway?
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• B
• D • P |
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Draw and label the complement cascade to MAC
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Which complement proteins do all pathways include?
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• C3
• C5 • C6 • C7 • C8 • C9n |
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Describe opsonization
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•Through the process of complement of complement activation and fixation, the resultant C3b binds to the microbe
•The C3b on the microbe is stimulates phagocytosis by phagocytes |
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Describe inflammation
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•Chemotaxis stimulation by C3a, C4a & C5a enhances inflammatory effect
•These proteins bind to basophils & mast cells causing them to release histamine •C5a together with cytokines signal phagocytes to leave bloodstream |
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How does the alternative pathway differentiate between host and bacteria?
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Host cells have DAF that blocks Factor B binding, and Factor H that signals Factor I, which destroys the complex of C3b
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How does a bacterial capsule prevent complement?
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• Encapsulated bacteria binds to protein H which results in elimination of C3b binding
• This disrupts complement cascade |
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What are cytokines?
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Signaling proteins produced in response to stimuli, and mediators of inflammation [septic shock]
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How are cytokines involved in clearing infection?
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Triggers release of monocytes and polymorphonuclear leukocytes to site of infection
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How do PMNs migrate from blood to infection site and which cytokines are involved?
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•PMNs force themselves between cells [assisted by Platelet-endothelial cell adhesion molecule [PECAM], C3a & C5a] causing vasodilation [assisted by Platelet activating factor [PAF]
•Once out of blood vessels, PMNs reach site through chemotaxis of C5a |
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What is involved in inflammation?
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•Complement activation
• Cytokine release •PMN transmigration & activation •Production of leukotrienes & prostaglandins |
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Why are you more likely to get sick while under stress?
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•Sympathetic neurons & hypothalamic adrenal cortex-pituitary axis influence system
•Cytokine & specific immunity are down regulated in stressed individuals •Norepinephrine & epinephrine also suppress immune cells |
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What is septic shock?
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•Condition resulting from high levels of bacteria and their products in blood
•Causes multiple organ dysfunction/failure •Can quickly lead to death |
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What are the stages of septic shock?
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•Stage I
o Fever greater than 38oC or less that 36oC o Rapid heart rate o Increased respirations o Unnatural high/low neitrophil count •Stage II o Sepsis [full-body inflammatory state] •Stage III o Organ dysfunction & low blood pressure Despite fluid administration |
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What is active immunity and how is it acquired?
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Immunity created when a person’s own immune system responds to specific infectious agents
• Naturally acquired: exposure to infectious agent • Artificially acquired: vaccination/chemoprophylaxis |
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What are the functions of T lymphocytes & B lymphocytes?
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Cells for specific immunity
• T cells carry out cell mediated immunity • B cells initiate the release of cytokines |
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Compare humoral and cell mediated immunity
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What is humoral immunity?
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Antibody mediated immunity involving IgG and other humoral antibodies
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What is cell mediated immunity?
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Acquired immunity due to T cells and activated macrophages [does not involve antibodies
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What is an antibody?
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an immunoglobulin molecule that interacts with an antigen
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What are the different classes of antibodies?
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• IgG: main antibody in circulation
• IgM: largest antibody found in circulation • IgA: found in secretions • IgE: antigen receptor on basophils and mast cells • IgD: surface of immature B cells |
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What are the mechanisms of antibody action?
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5 Ways
• Direct action • Agglutination/aggregation • Opsonization • Lysis • Inflammation |
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What are the types of antigen presenting cells?
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• Macrophages
• Dendritic cells • B Cells |
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How do antigen presenting cells present antigens to lymphocytes?
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APCs degrade protein antigens and display peptides on surface [MHC-I & MHC-II]
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What do helper T cells [TH] do?
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• Th1: activates cytotoxic T cells, macrophages & B cells
• Th2: activates eosinophils, stimulats B cells to produce IgG & IgE |
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Describe cytotoxic killing
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• Triggering of apoptosis stimulates production of perforin and granulysin
• Perforin binds to target cell and forms holes causing contents to leak out • Granulysin kills intracellular pathogens by disrupting proton motive force |