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Sketchy Micro > B1. Gram positives > Flashcards

B1. Gram positives Flashcards

1
Q

What is the gross appearance of the colonies for staph aureus?

A

Grape-like clusters

Golden yellow colonies

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2
Q

How do you tell apart staph and strep?

A

staph are all catalase positive

catalase is enzyme that converts H2O2 to water

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3
Q

How do you tell staph aureus apart from the other staphs?

A

S. aureus is coagulase positive, all other Staphs are coagulase negative

Coagulase is enzyme that converts fibrinogen to fibrin

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4
Q

What are the five characteristics on a petri-dish that you would see with staph a?

A
  1. Gram positive (violet)
  2. Catalase positive (tells you its staph)
  3. Coagulase positive (tells you its staph a)
  4. Beta-hemolytic (hemolysis of blood)
  5. Ferments mannitol (agar turns yellow)
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5
Q

What is the main virulence factor for staph a?

A

Protein A

is a component of the cell wall that binds the Fc portion of antibodies, preventing opsonization

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6
Q

What are the nine diseases caused by staph a?

A 
Pneumonia
Septic arthritis
Skin infections - abscesses
Acute bacterial endocarditis
Osteomyelitis
Scalded-skin syndrome
Toxin shock syndrome
Staph food poisoning
MRSA
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7
Q

What is the appearance on x-ray film of a staph aureus infections?

A

patchy infiltrate

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8
Q

What is the most common cause of septic arthritis?

A

Staph aureus

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9
Q

Where does staph aureus like to colonize?

A

nares

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10
Q

What is the most common cause of osteomyelitis in adults?

A

staph aureus

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11
Q

What are the toxin-mediated diseases caused by staph aureus?

A

Scalded-skin syndrome (expholiative toxin)
Toxin shock syndrome (leaving in a foreign body too long, TSS is a superantigen causing overactivation and cytokine storm)
Food poisoning - pre-formed toxin causes acute vomitting due to meats and mayo

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12
Q

What is altered in MRSA?

A

penicillin binding proteins that are part of cell walls

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13
Q

How do you tx MRSA?

Methicillin-sensitive staph?

A

MRSA: Vancomycin

Methicillin-sensitive is treated by nafcilin (Naf for Staf)

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14
Q

What is the most common cause of endocarditis of artificial heart valves?

A

Staph epidermis

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15
Q

How do you treat a staph epidermidis ifx?

A

vancomycin

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16
Q

What organism is usually linked to infections that arise from prosthetic joints, indwelling catheters

A

staph epidermidis

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17
Q

Why doe staph epidermidis cause blood culture contamination so much?

A

Because it’s part of the normal skin flora, so it’s easy for it to contaminate samples (e.g. drawing blood through needle)

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18
Q

How do you tell the difference between staph aureus and staph epidermidis/saprophyticus

A

Staph aureus is coagulase positive

Staph epidermidis/saprophyticus is coagulase negative

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19
Q

How do you tell the difference between staph epidermidis and saprophyticus

A

Novobiocin sensitivity

Novobiocin sensitive = S. epidermidis
Novobiocin resistant = S. saprophyticus

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20
Q

Which staph bacteria produces biofilms?

A

S. epidermidis

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21
Q

What is a common cause of UTIs in sexually active female?

A

S. saprophyticus

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22
Q

Relate the following characteristics for staph saprophyticus: coagulase, catalse, urease

A

Catalse + (so it’s staph)
Coagulase - (so it’s not staph a)
Urease + (so it’s s. saprophyticus)

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23
Q

What does urease do?

A

converts urea to ammonia

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24
Q

What does coagulase do?

A

Coagulase converts fibrinogen to fibrin

25
Q

What does catalase do?

A

Converts H2O2 to water

26
Q

What does beta-hemolytic mean?

A

Complete hemolysis of rbc

27
Q

Fermenting mannitol turns the agar what color?

A

Yellow

28
Q

What bacteria is considered to be Group A Strep?

A

Strep pyogenes

29
Q

Which strep is encapsulated and contains hyaluronic acid? is it immunogenic?

A

Group A strep pyogenes

No, not immunogenic

30
Q

What three skin infections does Group A strep cause?

A

Impetigo (honey crusted)
Pharyngitis (strep throat)
Erysipela and cellulitis

31
Q

What is the most common cause of erysepilas

A

S. pyogenes

32
Q

What are the three toxin-mediated diseases of Strep pyogenes?

A

Scarlet fever, toxic shock-like syndrome, necrotizing fasciitis

33
Q

What are the three characteristics of scarlet fever

A
  1. Strawberry tongue
  2. Pharyngitis
  3. Wide-spread rash sparring the face
34
Q

What is necrotizing fasciitis? What causes it?

A

Necrotizing invades fascia underlying skin and spreads rapidly
Caused by GAS (SPE-B)

35
Q

What are SPE-A, SPE-B, SPE-C? What do they cause?

A

SPE = strep pyrogenic exotoxin

A, C cause Toxic shock-like syndrome
B causes necrotizing fasciitis

36
Q

M Protein, which bac? What does it do?

What does it lead to?

A

Found in GAS (pyrogenes)
Main virulence factor
Interferes with opsonization = antiphagocytic

Induces strong humoral response = autoantibody production against cardiac myosin, leading to damaged heart valves

THIS IS RHEUMATIC FEVER

37
Q

What valve is most likely damaged with a staph aureus infection?

A

Tricuspid valve (due to right-sided endocarditis)

38
Q

What valve is most likely damaged with a strep pyogenes GAS infection?

A

Mitral valve

39
Q

What are the symptoms of rheumatic fever?

A

J - polyarthritis
O - heart problems (valve damage –> murmurs, myocarditis, pericarditis)
N - subcutaneous Nodules
E - erythema marginatum
S - Sydenham’s chorea (rapid involuntary movements of hands and face)

40
Q

What is Sydenham’s chorea? What infection and condition do you see it with?

A

Rapid involuntary movements of hands and face
GAS
Rheumatic fever

41
Q

What bacterial infection do you see PSGN in?

A

GAS (pyogenes)

42
Q

How long after a GAS infection do you see PSGN?

A

2 weeks

43
Q

What are some clinical features of PGSN?

A

Dark brown or cola colored urine

facial swelling and puffiness (edema)

44
Q

What are the two ways to tell RF and PSGN apart?

A
  1. RF occurs after pharyngitis, PSGN occurs after pharyngitis or skin infection
  2. Early dx and tx of strep throat can prevent RF but not PSGN
45
Q

How do you treat GAS?

A

Penicillin

46
Q

What are the three main virulence factors for GAS?

A
  1. Stretolysin O
  2. Stretokinase
  3. DNase
47
Q

What does Stretolysin O do? CLinical significance?

A

Allows bac to lyse RBC and do beta-hemolysis

AB generated against SO. ASO titers reveal strep infection occurred recently

48
Q

What does stretokinase do? Clinical significance?

A

Converts plasminogen –> plasmin (which is fibrinolytic)

Given as medication to bust clots. Used in MIs, strokes, etc

49
Q

How do you tell apart GAS and GBS in terms of antibiotics?

A

GAS (pyrogenes) is bacitracin SENSITIVE

GBS is bacitracin RESISTANT

50
Q

What is the enzyme that cross links the dissachs in the CW to make the peptidoglycan layer?

What inactivates this enzyme?

Another name for this enzyme?

A

Tanspeptidase located in the inner cytoplasmic
membrane

Penicillin binds to
and inhibits it. For this reason the enzyme is
also called penicillin binding protein

51
Q

What is the importance of teichoic acid?

A

Polysacch present in gram (+) bacteria

Important for identification of bacteria

52
Q

Group B strep is what organism?

A

S. agalactiae

53
Q

The hippurate test tells you what?

Which organism is positive for the hippurate test?

A

(+) Hippurate test shows that organism can hydrolyze hippurate

GBS (S. agalactiae)

54
Q

What is the CAMP test? Which organism is positive for CAMP test?

A

CAMP test is when you plate organism with S. aureus. (+) CAMP means that the zone of hydrolysis increased w/ S. aureus presence

GBS (agalactiae)

55
Q

What sets S. agalactiae apart from GAS?

A

Bacitracin resistant

56
Q

How do you tell if S. agalactiae is different than strep pneumo and viridans?

A

S. agalactiae is beta hemolytic

57
Q

What is the no. 1 cause of meningitis in neonates?

A

S. agalactiae

58
Q

S. agalactiae causes which diseases? (3)

A
  1. meningitis in neonates
  2. sepsis
  3. pneumonia
59
Q

How does a neonate contact GBS? What is done to prevent this?

A

During delivery, if mother has GBS in vaginal canal, baby will get GBS infection

Penicillin is given prophylactically

Sketchy Micro (1 decks)

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