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Microbiology (bacteria) > staphylococci > Flashcards

staphylococci Flashcards

1
Q

three staphylococcus species

A

1) aureus
2) epidermidis
3) saprophyticus

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2
Q

staphylococcus shape and gram stain

A

all gram positive cocci

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3
Q

what is coagulase?

A

clots human/rabbit plasma by activating fibrinogen

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4
Q

which staph species are coagulase positive?

A

only aureus, the other two are negative

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5
Q

what is catalase?

A

converts peroxide to oxygen and water

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6
Q

is staph catalase positive or negative?

A

positive, in contrast to strep which is negative

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7
Q

what is the metabolic characterization of staph?

A

facultative anaerobe

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8
Q

S. aureus, where found?

A
  • skin, mucous membranes, nares of normal individuals

- nasal passages up to 30-40%

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9
Q

S. aureus risk factors

A
  • foreign bodies, catheters
  • hospitalized/immunocompromised
  • diabetes
  • drug addiction
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10
Q

S aureus pathogenesis of toxin-mediated disease

A
  • enterotoxins via food/tampon

- colonization/toxin production in host - colonization via fibrinogen/fibrinogen receptors on bacteria

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11
Q

important S. aureus toxins

A
  • toxic shock syndrome toxin - toxic shock syndrome

- exfoliatins - scalded skin syndrome

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12
Q

S. aureus pathogenesis of invasive disease

A
  • bacterial surface adhesion molecules bind to matrix proteins such as fibrinogen, fibronectin, collagen, and platelets
  • matrix proteins found on damaged skin, disrupted airway epithelium, or endothelial cells in bloodstream
  • after adhesion, colonization, evasion of host response, toxin synthesis, cell lysis, spreading to other sites
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13
Q

S. aureus toxins and enzymes for cell lysis

A
  • alpha toxin - lyse membranes
  • leukocidins - lysis of leukocytes
  • proteases - breakdown of host proteins
  • coagulase - clots human plasma
  • staphylokinase - lysis of blood clot
  • hyaluronidase - dissolve hyaluronic acid, component of matrix
  • lipase - dissolve lipids and lipoproteins
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14
Q

S. aureus toxins and enzymes for evasion of host immune response

A
  • protein A - cell wall protein binds to host IgG via Fc receptors, less complement-mediated killing, B-cell super antigen leading to defective production of IgM
  • enterotoxins A-E, G-I, T-cell superantigens, blunting of T-cell response
  • capsular polysaccharides - anti-phagocytic
  • Eap (Map) - surface protein that impairs neutrophil recruitment
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15
Q

S. aureus toxin-mediated diseases

A
  • food poisoning
  • toxic shock syndrome
  • staph scalded skin syndrome
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16
Q

S. aureus food poisoning causes and clinical syndromes

A
  • enterotoxins A-E, G-I
  • can resist boiling
  • A and C are super antigens stimulating IL-1, IL-2, TNF
  • nausea, vomiting, non-bloody diarrhea
17
Q

S. aureus toxic shock syndrome causes and clinical syndromes

A
  • enterotoxin F (TSST-1)
  • tampon use or open wounds
  • superantigen stimulates IL-1, 2, TNF
  • fever, rash, desquamation of palms and soles, hypertension, shock
18
Q

S. aureus scalded skin syndrome causes and clinical syndromes

A
  • exfoliatins A and B
  • only secreted by phage group II
  • seen in infants
  • erythematous skin, exfoliation
  • epidermis detaching from dermis in response to toxin
19
Q

immunological nature of S. aureus toxin mediated infections:

A
  • most caused by super antigen effect so antibiotics often not effective by the time the syndrome is present
20
Q

treatment of staph aureus invasive infections

A
  • surgical drainage of abscesses

- synthetic penicillin, vancomycin as last resort

21
Q

S. aureus colony color

A

yellow

22
Q

S. epidermidis colony color

A

white

23
Q

S. saprophyticus colony color

A

white

24
Q

distinguishing S. epidermidis from S. saprophyticus

A

S. epidermidis is sensitive to novobiotin, which S. saprophyticus is not.

25
Q

S epidermidis, where found?

A

skin, normal flora

26
Q

who most susceptible to S. epidermidis?

A

neonates, patients with renal failure, immunocompromised

27
Q

S. epidermidis pathogenesis

A
  • colonizes prosthetic surfaces very efficiently
  • bacteremia, but slower than S. aureus
  • ## BIOFILM
28
Q

S. epidermidis clinical syndromes

A
  • low grade fever, pain, discomfort about prosthetics

- may be a contaminant in blood culture so treat patient, not culture

29
Q

treatment for S. epidermidis:

A
  • remove prosthetics if feasible
  • vancomycin
  • consider rifampin and/or gentamicin if toxic
30
Q

S. saprophyticus clinical syndromes

A
  • second most common cause of UTI after E. coli

- polyuria, dysuria

31
Q

S. saprophyticus, where found?

A

skin

32
Q

S. saprophyticus treatment

A
  • trimethoprim sulfamethoxazol (bactrim)

- norfloxacin (quinolone)

Microbiology (bacteria) (16 decks)

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