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70 Cards in this Set
- Front
- Back
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Gram positive cocci that have a positive catalase test gives what type of cocci?
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- stphylococcus/micrococcus
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Positive coagulase test gives what type of cocci?
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- staphylococcus aureus
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A negative coagulase test gives what type of cocci?
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- Coagulase negative staphylococci (ie S epidermidis)
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What does S aureus look like when plated?
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- yellow-gold
- hemolytic |
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What does Coagulase negative staphylococcis look like when plated?
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- white
- non-hemolytic |
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What does a coagulase test actually test?
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- coagulase is an enzyme that causes plasma to clot by activating prothrombin to thrombin , thus activating fibrinogen
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What is the normal habitat of staphylococci?
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- anterior nares
- mucous membranes - skin - GI tract - Vagina |
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What are 5 of S. aureus' virulence factors?
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1) Protein A
2) Fibronectin-binding protein 3) hemolysins 4) panton-valentine leukocidin (PVL) 5) secreted enzymes |
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What is protein A?
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- S. aureus
- major cell wall protein - binds to Fc of IgG, preventing complement |
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What does fibronecting-binding protein do?
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- S. aureus
- promotes binding so bacteria can get entrance to host |
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What is hemolysins?
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S. aureus
- Beta-hemolysin damages cell membranes - y-toxin lyses WBCs |
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What is Panton-Valentine Leukocidin (PVL)?
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S. aureus
- Carried on SCCmec IV 'pathogenicity island'~ mobile genetic element that can integrate itself into new bacterial chromosomes - associated w severe infections (skin, hemorrhagic pneumonia) |
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What is SCCmec IV 'pathogenicity island"?
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- SCC= staphylococcal cassette chromosome
- mec = genetic element conferring resistance to methicillin (MRSA has mec gene) |
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What are some enzymes secreted by S aureus?
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- lipases, proteases, DNAses
- hyaluronidase (hydrolyzes connective tx matrix) - Catalse (counteracts neutrophils' ability to kill bacteria) - Coagulase (fibrinogen to fibrin, prevents phagocytosis b/c WBC cant get to infection) |
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What are the 3 superantigen toxins of S. aureus?
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Staphylococcal Scaled Skin Syndrome Toxin
- ETA and ETB cause Toxic Shock Syndrome Toxin - TSST-1 causes Enterotoxins types A-G - food poisoning, heat stable |
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What do Super Antigens do?
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- bind MHC class II to VB region of T cells, inducing large T activate of cytokines
- Bypass APC processing/presenting, so lose T cell specificity to Ag |
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What are some examples of diseases caused by S aureus?
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- abscess formation
- skin/soft tx infections - bactermia - endocarditis - pneumonia - osteomeitis - septic arthritis - nosocomial infections - gastroenteritis/food-poisoning |
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What is cellulitis/what causes it?
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S. aureus
- subcutaneous inflammation - spreads via lymph/blood |
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What is impetigo/what causes it?
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S. aureus
- vesicular, crusted, superficial - goden-yellow, crusts |
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What is erysipelas/what causes it?
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S. aureus
- superficial cellultis - prominent lymphatics - bright red, puffy with fluid, sharp border btw infected/normal skin |
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What is SSSS, what causes?
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S. aureus
- superficial skin, blistering to scalding - caused by ETA/ETB - almost only in newborns, under 1 year |
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What is Toxic Shock syndrome, what causes?
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S aureus
- caused by TSST-1 - high fever, rash, skin peeling, vomiting, diarrhea, hypotension, multiorgan involvement |
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What causes S aureus toxin-mediated gastroenteritis/food poisoning
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- enterotoxins A-G
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What antibiotic is most S aureus resistant to?
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- penicillin
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What does MecA do?
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- doesn't allow binding for methicillin (PB2A)
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What is the most prominent type of Coagulase-Negative Staphylococci?
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- S epidermis
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What is beta hemolysis
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- complete hemolysis where rbcs are completely lysed
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What is alpha hemolysis
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- partial hemolysis of rbcs
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What is gamma hemolysis?
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- no hemolysis of rbcs
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What type of cocci have a negative catalase test?
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- Streptococci
- Enterococci |
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what are some beta-hemolytic cocci?
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- Group A (s pyogenes)
- Group B (s agalactiae) |
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What are some alpha hemolytic cocci?
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- S pnemuonia
- viridan strep |
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What is non-hemolytic alpha?
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- group D: enterococci and Group D non-enterococci
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What are beta-hemolytic streptococci classified by?
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- C- carbohydrate (cell wall component)
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Group A streptococcus is susceptible to what antibiotic?
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- bacitracin
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What are the virulence factors of S pyogenes?
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1) hyaluronic acid capsule-antiphagocytic and non immunogenic (looks like host and inhibits phagocytosis)
2) fimbriae contain M protein 3) protein F mediates attachment 4) streptococcal pyrogenic exotins 5) C5a peptidase 6) streptolysin O and S 7) hyaluronidase 8) streptokinase 9) DNases |
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What is streptococcal pyrogenic exotoxins
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- Spe A/C super antigens
- similiar to staph infections |
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What is C5a peptidase
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S pyogenes
- prevents attraction of phagocytic cells to infection |
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What does streptokinase do?
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- dissolves clot
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What are streptolysin O/S and what do they do?
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- O= labile
- S = stable they are cytolysins and can lyse leukocytes, platelets, RBC, etc |
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What do hyaluronidases do?
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S pyogenes
- promotes spread ofinfection |
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What do streptokinases do?
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- dissolve clots that allows infection to spread
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What are some likely S pyogenes infections?
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- **pharyngitis
- tonsillitis - mastoiditis - pneumonia - impetigo - erysipelas - cellulitis - necrotizing fascilitis - myositis |
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Pharyngitis is most commonly caused by which group of cocci?
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- Group A streptococci
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Give 2 examples where antibiotics are givien post infectious sequelae for S pyogenes
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- Acute rheumatic fever
- acute glomerulonephritis |
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Why is acute rheumatic fever associated with S pyogenes?
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- cross reaction btw Ag of hear and streptococcal
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What is the relationship between acute glomerulonephritis and S pyogenes?
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- may occur after impetigo/pharyngitis
- antibiotic therapy doesn't prevent - Caused by Ag-Ab complexes collecting in glomerular basement membrane |
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What is a toxin mediated infection of S pyogenes?
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- Scarlet fever
- Streptococcal toxic shock syndrome |
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Describe scarlet fever
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- rash after 2nd day with pharyngitis that begins on trunk and goes out
- tongue goes from white/strawberry to red strawberry |
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What is streptococcal toxic shock syndrome caused by?
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- pyrogenic toxins Spe A and C
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What group does streptococcus agalactiae belong to?
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- group B
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Where is S agalactiae normally and what can it cause?
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- GI, female genital tracts
- sepsis, meningitis, pneumonia (newborns, elderly, immunocompromised) |
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What is the relationship between pregnant women and S agalactiae?
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- if women are positive for Group B streptococci, mothers are given antibiotics upon delivery
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Streptococcus pneumonia belongs to what class?
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- alpha hemolytic
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P disk is for what drug?
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- optochin (P for S. pneumonia)
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What infections can S pneumoniae cause?
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- pneumonia
- otitis media - bactermia and meningitis - predisposed to other infections |
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What is the major and minor virulence factors for S pneumoniae?
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- polysaccharide capsule
- autolysisn which release pneumolysin |
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What is the role of polysaccharide capsules play in vaccine production?
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- children over 5: given vaccine with Ag (Ti Ag)
- children under 5: given vaccine with 9 capsular Ag conjugated to diphtheria toxin to initiate Td Ag |
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What does pneumolysin do?
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- attacks cell membranes
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What class does Viridans streptococci belong to?
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- alpha- hemolytic
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Where is viridan streptococci supposed to be?
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- normal flora mouth/oropharynx
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What can viridans streptococci cause?
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- abscesses in brain, liver, abd cavity
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How is Enterococci classified?
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- non hemolytic or alpha hemolytic
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What Ag does Enterococci contain?
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- Group D
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What does Enterococci mainly cause?
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- UTI, endocarditis, intra-abd infections, bactermia
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Vancomycin resistan enterococci is usually associated with which species of Enterococci?
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- E. faecium
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What antibiotics is S pneumoniae most likely to be resistant against?
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- penicillin, erythromycin, clindamycin, trmethoprim/sulfamethoxazole
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Viridans streptococci are resisitant against?
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- penicillin
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Groups A,B,C, G beta-hemolytic streptococci are susceptible to which antibiotic?
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- penicillin
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Enterococci are resistant against?
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- penicillin, vancomycin
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