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70 Cards in this Set

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