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109 Cards in this Set
- Front
- Back
definition: PATHOGEN
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infectious agent that has the ABILITY to cause disease in a particular host
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strict pathogen
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always pathogenic
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opportunistic pathogen
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pathogenic in immunocompromised host or when introduced to unprotected site
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virulence
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degree of pathogenicity
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virulence factor+
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property that enhances ability of microorganism to cause disease
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carriage
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host colonized with a pathogen, but no overt symptoms of disease
can still be infectious can be transient or long-term |
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latent
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infectious agent present, not growing, can reactivate
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commensal
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part of normal flora
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infectious dose
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# of organisms required to cause disease
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Koch's First Postulate
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organism must always be found in diseased animals, but not in healthy ones
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Koch's Second Postulate
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organism must be isolated from diseased animals and grown in pure culture away from the animal
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Koch's Third Postulate
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organism isolated in pure culture must initiate and reproduce the disease when reinoculate into susceptible animals
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Koch's Fouth Postulate
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organism should be reisolated from experimentally infected animals
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Modified Koch's Postulates for molecular biology (1)
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1. gene must be identified from virulent microorganism
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Modified Koch's Postulates for molecular biology (2)
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2. gene must be inactivated by methods which do not allow reversion in original strain, constructing an isogenic strain that is negative for that gene
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Modifed Koch's postulates for molecular biology (3)
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3. strain w/ inactivated gene must be shown to be avirulent or to have measurably reduced virulence
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Modified Koch's postulates for molecular biology (4)
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reintroduction of the WT gene into the iosgenic negative strain should lead to a return of original virulence
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5 steps of typical infectious cycle
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entry of the pathogen
colonization avoidance of host defenses damage to the host exit |
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4 reservoirs of infection
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environment
infected persons infected animals self |
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5 routes of transmission
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airborne/respiratory
oral-fecal direct inoculation direct contact congenital |
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host defenses in upper respiratory tract (URT)
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mucous lining
ciliated cells on lining secretory immune system, eg: IgA alveolar Mphages normal microbiota |
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4 examples of airborne pathogens
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Legionella
N. meningitis M. tuberculosis S. pyogenes |
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host defenses against oral-fecal transmission
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intact intestinal mucosal epithelium
secretory immune system & IgA bile, acid, digestive enzymes peristalsis normal microbiota |
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4 oral-fecal transmitted bacteria
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V. cholerae
E. coli Salmonella Shigella |
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host defenses against direct inoculation
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intact skin barrier
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examples of direct inoculation
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most staph infections
deep wound infections (tetanus, gangrene) disease spread by insect vectors disease spread by transfusion man zoonotic infections |
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4 examples of diseases spread by insects
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malaria
plague typhus arboviral diseases |
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host defenses against direct contact transmission
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intact epithelial surface
mucosal secretory immune system |
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examples of diseases transmitted by direct contact
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skin diseases, eg: impetigo, athlete's foot
mucosal infections: STDs, conjunctivitis, trachoma, herpes |
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host defenses against congenital transmission
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placenta
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examples of transplacentally transmitted diseases
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congenital rubella
congenital syphilis |
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examples of diseases transmitted at birth
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any STD
herpes group B strep |
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colonization
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attachment of a microorganism to host tissues and its multiplication on these surfaces
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adhesins
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attachments factors on invading organism
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receptors
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factors on host cells recognized and bound by adnesins
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2 protein types used in colonization
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adhesins
receptors |
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5 examples of bacterial adhesins
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E. coli Pap pili
Streptococcal F protein Mycoplasma pneumoniae membrane protein Neisseria pili Vibrio cholerae |
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3 factors other than adhesins/receptors that affect attachment
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motility
mucinases IgA1 proteases |
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during colonization, bacteria can attach to what 3 things
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inanimate objects (biofilms)
other microbes other microbe communities |
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biofilms
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cooperative behavior of a bacterial population wherein the bacteria adhere to one another as well as a surface
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function of biofilm
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facilitates colonization
prevents washing away |
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communities of bacteria morphologically and physiologically differentiated from free-living bacteria
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biofilms
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can biofilms be composed of multiple species?
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yes
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quorum-sensing
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involves production and sensing of small molecules called bacterial pheronomes
facilitates cell-cell communication |
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prosthetic valve
bacteria that form biofilms disease that results |
S. epidermis
S. sanguis --> endocarditis |
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artificial heart
bacteria that form biofilms disease that results |
P. aeruginosa
S. aureus S. epidermis --> septicemia |
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IV catheters
bacteria that form biofilms disease that results |
Staphylococcus epidermidis
Staphylococcus aureus --> septicemia, endocarditis |
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urinary catheters
bacteria that form biofilms disease that results |
P. aeruginosa
proteus mirabilis E. coli E. faecalis --> bacteriuria |
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contact lensesq
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P. aeurinosa
S. epidermidis --> keratinitis |
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type of biofilm that causes periodontal disease
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usually mixed communities
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species that forms biofilm in CF lung
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P. aeruginosa
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species that forms biofilms in environment, but is planktonic in gut
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V. cholerae
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bacterial disease
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result of bacterial invasion
& sometimes host response to invasion --> damage to host |
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3 mechanisms used by pathogens that cause disease
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direct damage by toxins and enzymes
penetration and destruction of host cells indirect damage by immunopathologic reactions |
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toxin
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molecule produced by bacterium that is
RELEASED to affect host cells at a distance |
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two means of toxin release
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shed
actively secreted |
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exotoxin
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protein released from bacterial cell that is toxic for target cells or animals
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endotoxin
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LPS
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cell wall components that mediate toxicity
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petidoglycan (G+ and G-)
techoic and lipotechoic acid (G+) |
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what type of bacteria is LPS never found in?
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G+
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effects of LPS
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stimulation of Mphages, B-cells and other cells to multiply and release cytokines, inflammatory molecules
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LPS always lacking O-antigen
name 2 bacteria type |
LOS
Neisseria Haemophilus |
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LPS sometimes lacking O-Ag
name bacteria |
rough LPS
Salmonella |
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LPS shed by bacterial cells forms a complex with WHAT, WHERE?
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with an LPS-binding protein
in serum |
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what does LPS-protein complex bind on WBCs?
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CD14 receptors
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what does LPS bind on endothelial cells (besides CD14R)
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TLR4
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proinflammatory cytokines triggered by endotoxins
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IL-1, IL-6, TNF-a, IL-12
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3 inflammatory mediators triggered by endotoxins
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PGs
LTs kinins |
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do endotoxins initiate adaptive immune response?
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yes
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at LOW concentrations, endotoxins are _____
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immunostimulants, eliciting protective responses
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4 effects of LOW concentration endotoxin
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fever
increased phagocytic ability increased Ab synthesis vasodilation |
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HIGH concentrations of endotoxin lead to...
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hypotension and shock
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shock
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widespread hypoperfusion of tissues
due to reduction in blood volume or cardiac output --> inadequate circulating volume |
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3 types of shock
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endotoxic
cardiogenic hypovolemic |
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3 types of exotoxins
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neurotoxins
enterotoxins cytotoxins |
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3 types of endotoxins by morphology
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AB subunit toxins
cytolysins superAg toxins |
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AB subunit exotoxin mechanism of action
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ADP-ribosylation
A subunit is ADP-ribosyl transferase transfers ADP-ribose from NAD to some host protein, resulting in host protein inactivation |
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3 examplse of ADP-ribosylation
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diphtheria toxin
cholera toxin tetanus and botulinism toxin |
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phospholipases
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hydrolyze membrane phospholipids and destabilize cell membranes
e.g.: Clostridium perfringens alpha-toxin |
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superAg toxins
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protein toxins that exert their effect by forming a bridge btw MHC class II of Mphages and V-beta portion of TCR
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do superAg toxins need to be processed by APCs to be effective?
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NO
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2 things superAgs stimulate
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T-cells
B-cells |
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how are superAgs different from true mitogens
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true mitogens stimulate ALL T-cells to proliferate
SuperAg's only activate T cells expressing certain TCR V-beta proteins |
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how are superAgs different from normal Ags?
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normal Ags activate a single or very limited subset of lymphocytes expressing TCRS specific for that Ag
SuperAg's activate all T cells expressing certain TCR V-beta proteins |
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extracellular enzymes, aka:
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spreading factors
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4 types of spreading factors
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collagenases
proteases hyaluronidase DNase |
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chemical nature of endotxins vs. exotoxins
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endotoxins - lipopolysaccharides
exotoxins - proteins |
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which are more strongly neutralized by Ab's, endo- or exotoxins?
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exotoxins are more strongly neutralized by Ab's
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which are stable to boiling, endotoxins or exotoxins?
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endotoxins are stable to boiling
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which stimulates B cells, endotoxins or SuperAg's?
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both
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which stimulates T cells, endotoxins or superAg's?
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superAg's
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which bridges MHC II and TCRs, endotoxins or superAg's?
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superAg's
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which stimulates IL-1 and TNFa, endotoxins or superAg's?
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both endotoxins and superantigens
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which stimulates coagulation cascade, endotoxins or superAg's?
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endotoxins only
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which stimulates fibrin cascade, endotoxins or superAg's?
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endotoxins only
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non-professional phagocytes
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host cells that are not normally phagocytic but can be induced to take up a bacterial pathogen by PATHOGEN-SPECIFIED receptor-mediated endocytosis
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bacterial mechanisms to avoid phagocytic killing
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prevention of maturation of phagolysosome
alteration of phagosome escape from phagosome |
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bacteria that survive w/in professional phagocytes trigger their own uptake into the cells by binding to which phagocyte surface receptors?
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C3b
fibronectin receptors |
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proteins that bind to host cell receptors and induce uptake into non-professional phagocytes
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invasins
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zipper mechanism of host cell invasion
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invasin binds to host cell receptor and "zips" the host cell membrane around the bacterium by sequential binding
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trigger mechanism of host cell invasion
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bacterial type III secretion system injects one or more proteins into host cell
triggers membrane ruffling, including actin polymerization and cytoskeletal rearrangements |
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coiling phagocytosis mechanism of host cell invasion
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characteristic of L. penumophila
occuras spontaneously with Legionella via interaction between bacterial porin and complement coils form around organism and phagosome " sinks" into cell |
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what 2 things does zipper mechanism require
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host cell actin network
host cell signaling via tyrosine kinase |
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2 examples of zipper mechanism
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Yersinia species INVASIN binds beta-1 integrin
Listeria monocytogenes INTERNALIN binds E-cadherin |
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In zipper mechanism, bacterium is taken up into a ____ or ____
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membrane-bound vacuole or phagosome
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4 things trigger mechanism requires
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energy expenditure by host cell
actin and microfilament network host cell signaling cascades metabolically active bacteria |
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host cell entry mechanism that does not disrupt integrity of host cell
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trigger mechanism
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2 examples of bacteria that use trigger mechanism
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Salmonella typhimurium SipB-D proteins
Shigella dysenteriae IpaB-D proteins |
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3 types of indirect damage by immunopathologic reactions
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induction of cross-reacting antibodies, e.g.: S. pyogenes and heart tissue
dposition of immune complexes in tissue, e.g.: glomerulonephritis (Type III reaction) Delayed hypersensitivity and granuloma formation e.g.: TB (type IV reaction) |