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NBME Micro > Bacteria: Gram Positive Cocci > Flashcards

Bacteria: Gram Positive Cocci Flashcards

1
Q

Staph Aureus is _______ positive

A
  1. gram positive
  2. catalase
  3. coagulase
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2
Q

Staph Aureus Shape

A

Cocci

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3
Q

Coagulase converts

A

fibrinogen to fibrin, forming a clot in samples

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4
Q

Staph Aureus are ___________ hemolytic

A

beta

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5
Q

Beta hemolytic species are able to

A

completely break down hemoglobin

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6
Q

Staph aureus bacteria _____ ______ mannitol

A

can ferment

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7
Q

Staphylococcus aureus bacteria can ferment mannitol

A

Staphylococcus aureus bacteria can ferment mannitol, turning mannitol salt agar yellow during culture (in contrast to most non-pathogenic staphylococci, which do not ferment mannitol)

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8
Q

Protein A

A
  1. Virulence Factor of Staph Aureus

2. Binds IgG in the Fc region, inhibiting complement activation and phagocytosis

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9
Q

Staphylococcus aureus is part of the normal flora of the

A

nares and skin

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10
Q

Staphylococcus aureus can cause

A
  1. Bacterial pneumonia
  2. Septic arthritis
  3. Impetigo
  4. Furuncles
  5. Carbuncles
  6. Erysipelas
  7. Cellulitis
  8. Acute Infective Endocarditis
  9. Rapid Onset Food Poisoning
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11
Q

Staphylococcus aureus can cause bacterial pneumonia, which appears as

A

patchy infiltrates on chest X-ray (compared to lobar infiltrates in Streptococcus pneumoniae)

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12
Q

Staphylococcus aureus pneumonia most commonly follows an

A

Staphylococcus aureus pneumonia most commonly follows an upper respiratory infection (especially influenza) due to weakening of the host immune system by the initial infection (known as superinfection)

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13
Q

Septic Arthritis

A

which presents with a warm, swollen, tender joint and purulent aspirate

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14
Q

Impetigo

A

pustules that rupture to form “honey crusted” lesions, especially on the face

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15
Q

Furuncles

A

Boils

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16
Q

Carbuncles

A

Communicating Furuncles

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17
Q

Acute infective endocarditis presents with

A

rapid-onset of fever, chills, tachycardia, and sepsis even in previously normal heart valves

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18
Q

Staphylococcus aureus is the most common cause of

A
  1. infective endocarditis (typically of the tricuspid valve), and is often seen with IV drug use, prosthetic valves, and previous valve damage
  2. osteomeyelitis
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19
Q

Some strains of Staphylococcus aureus produce

A
  1. exfoliative toxin (a tissue protease) that causes a diffuse desquamative rash (scalded skin syndrome)
  2. superantigen exotoxin (which binds MHC II to cause massive inflammation), resulting in fever, a desquamative rash, and sepsis (toxic shock syndrome)
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20
Q

Staphylococcus aureus is capable of producing a rapid-onset food poisoning presenting with

A

nausea and vomiting due to preformed exotoxin

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21
Q

Some strains of Staphylococcus aureus bacteria are resistant to

A
  1. beta-lactams

2. methicillin (MRSA)

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22
Q

Methicillin-resistant Staphylococcus aureus have

A

altered penicillin binding proteins, making it difficult or impossible for beta-lactams to adhere to their cell walls

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23
Q

Vancomycin is effective against

A

methicillin-resistant Staphylococcus aureus

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24
Q

Nafcillin (a beta-lactam) is effective against

A

non-MRSA Staphylococcus aureus

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25
Q

Staphylococcus epidermidis is _____ positive

A
  1. gram positive
  2. catalase
  3. urease
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26
Q

Staphylococcus epidermidis shape

A

cocci

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27
Q

List the gram positive cocci

A
  1. Staph Aureus
  2. Staph Epidermidis
  3. Staph Saprophyticus
  4. Strep Pyogenes
  5. Strep Agalacties
  6. Strep Pnuemonae
  7. Strep Viridans
  8. Enterococcus Faecium
  9. Enterococcus Faecalis
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28
Q

Staph Saprophyticus is ______ positive

A
  1. gram
  2. catalase
  3. urease
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29
Q

Staphylococcus epidermidis infection is associated with

A
  1. prosthetic joints

2. indwelling catheters

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30
Q

Staphylococcus epidermidis can cause

A

prosthetic valve endocarditis

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31
Q

Staphylococcus epidermidis produces

A

biofilms (extracellular polysaccharide matrix), allowing for adherence to prosthetic devices and IV catheters

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32
Q

_____ is effective against Staphylococcus epidermidis (most strains are resistant to nafcillin and methicillin due to the production of biofilms)

A

vancomyocin

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33
Q

Vancomycin is effective against Staphylococcus epidermidis most strains are resistant to

A

nafcillin and methicillin due to the production of biofilms

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34
Q

Staphylococcus epidermidis is a part of

A

the normal skin flora

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35
Q

Staphylococcus epidermidis is a common

A

blood culture contaminant

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36
Q

Staphylococcus epidermidis is susceptible to

A

the antibiotic novobiocin (differentiating it from Staphylococcus saprophyticus, which is novobiocin-resistant)

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37
Q

Staphylococcus saprophyticus commonly causes

A

uncomplicated urinary tract infections in young, sexually active females

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38
Q

Staphylococcus saprophyticus is novobiocin

A

resistant

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39
Q

Staphylococcus epidermidis is novobioicn

A

sensitive

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40
Q

Staphylococcus epidermidis and saprophyticus bacteria are _________ negative

A

coagulase-negative Staphylococcus species (CoNS) (differentiating them from Staphylococcus aureus, which is coagulase-positive)

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41
Q

Streptococcus pyogenes is also known as

A

group A strep

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42
Q

Streptococcus pyogenes is a

A

gram-positive coccus

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43
Q

Streptococcus pyogenes shape

A

coccus

44
Q

Streptococcus pyogenes (group A strep) bacteria are _______ hemolytic

A

beta-hemolytic (able to completely breakdown hemoglobin)

45
Q

Streptococcus pyogenes (group A strep) bacteria produce

A

a hyaluronic acid capsule

46
Q

Streptococcus pyogenes (group A strep) can cause

A
  1. impetigo
  2. streptococcal pharyngitis (strep throat)
    3.
47
Q

Impetigo

A

a superficial skin infection often presenting with “honey-crusted” lesions usually around the nose and mouth

48
Q

Streptococcus pyogenes (group A strep) is the most common cause of

A

skin infections, including cellulitis (infection of the subcutaneous tissue and skin with indistinct borders) and erysipelas (infection of the superficial dermis with sharp, indurated, raised borders)

49
Q

one of the characteristic findings in scarlet fever is

A
  1. strawberry tongue

2. diffuse desquamative “sandpaper” rash

50
Q

Scarlet Fever is

A

caused by the pyrogenic exotoxin of Streptococcus pyogenes (group A strep)

51
Q

Pharyngitis is a characteristic finding in

A

scarlet fever (caused by the pyrogenic exotoxin of Streptococcus pyogenes (group A strep))

52
Q

One of the characteristic findings in scarlet fever is diffuse desquamative “sandpaper” rash which is caused by

A

caused by the pyrogenic exotoxin of Streptococcus pyogenes (group A strep)

53
Q

One of the characteristic findings in scarlet fever is diffuse desquamative “sandpaper” rash that typically spares the

A

perioral area, palms, and soles

54
Q

The pyrogenic exotoxin of Streptococcus pyogenes (group A strep) is a

A

superantigen that causes widespread T-cell activation and inflammation, resulting in streptococcal toxic shock syndrome (STSS)

55
Q

Certain strains of Streptococcus pyogenes (group A strep) produce

A

pyrogenic exotoxin SpeB (a soft tissue protease) that leads to necrotizing fasciitis (a rapidly spreading infection of skin, subcutaneous tissue, and fascial planes)

56
Q

In rheumatic fever,

A

the M protein of Streptococcus pyogenes (group A strep) inactivates complement, prevents phagocytosis, and causes the formation of cross-reactive antibodies (molecular mimicry), leading to pancarditis and mitral stenosis

57
Q

The M protein of Streptococcus pyogenes (group A strep)

A

The M protein of Streptococcus pyogenes (group A strep) prevents phagocytosis by interfering with opsonization

58
Q

Cross-reactive antibodies formed against the M protein of Streptococcus pyogenes can cause

A

rheumatic heart disease → mitral regurgitation that can progress to mitral stenosis

59
Q

Rheumatic fever is caused by

A

untreated Streptococcus pyogenes (group A strep) pharyngitis (not caused by GAS soft tissue infection)

60
Q

the JONES criteria is used for

A

diagnosing acute rheumatic fever (“J” - joints (migratory polyarthritis), “♡” - myocarditis, “N” - nodules (subcutaneous), “E” - erythema marginatum, “S” - Sydenham chorea)

61
Q

Acute rheumatic fever commonly presents with

A

Migratory polyarthritis (usually large joints such as the elbow, knees, and ankles)

62
Q

Acute rheumatic fever can cause

A
  1. pancarditis affecting the pericardium, myocardium, and endocardium (valves)
  2. Sydenham chorea, which presents with rapid involuntary movement affecting all muscles throughout the body (and may show up 1-8 months after infection)
63
Q

Acute rheumatic fever can present with

A
  1. subcutaneous nodules (which form mostly on extensor surfaces of the forearm and may show central fibrinoid necrosis)
  2. a rash that consists of hive-like C-shaped areas of erythema (not to be confused with cellulitis)
64
Q

post-streptococcal glomerulonephritis is caused by

A

subepithelial immune complex deposition in glomeruli → renal damage and nephritic syndrome

65
Q

“cola-colored” urine from hemolysis is a common finding in

A

post-streptococcal glomerulonephritis (PSGN)

66
Q

post-streptococcal glomerulonephritis (PSGN) leads to

A

a nephritic syndrome several weeks after acute infection

67
Q

post-streptococcal glomerulonephritis can follow

A

Streptococcus pyogenes (group A strep) pharyngitis OR soft tissue infection

68
Q

prompt treatment of Streptococcus pyogenes (group A strep) pharyngitis with penicillin can prevent

A

rheumatic fever but not post-streptococcal glomerulonephritis

69
Q

post-streptococcal glomerulonephritis can develop after

A

streptococcal pharyngitis or soft tissue infection (even with treatment)

70
Q

antibodies against streptolysin O are used to diagnose

A

Streptococcus pyogenes (group A strep) pharyngitis

71
Q

streptolysin O is a

A

hemolytic virulence factor

72
Q

streptokinase of Streptococcus pyogenes (a virulence factor) is a

A

proteolytic enzyme that activates plasminogen → plasmin (which in turn degrades fibrin, preventing development of a fibrin barrier at the site of infection)

73
Q

antibodies against DNase (a virulence factor that liquefies purulent material) can be used to diagnose

A

Streptococcus pyogenes (group A strep) pharyngitis or soft tissue infection

74
Q

DNase is a virulence factor that

A

liquefies purulent material

75
Q

Streptococcus pyogenes (group A strep) is ______ sensitive

A

bacitracin

76
Q

antistreptolysin O titers can be used to diagnosis

A

acute rheumatic fever or post-streptococcal glomerulonephritis following pharyngeal infection (streptococcal skin infections are associated with a poor ASO response, so anti-DNAse titers should be checked as well to increase sensitivity)

77
Q

Streptococcus agalactiae

A
  1. group B strep
  2. a gram-positive coccus
  3. hippurate hydrolysis positive
  4. encapsulated
  5. beta hemolytic
  6. bacitracin resistant
78
Q

Streptococcus agalactiae (group B strep) produces

A

CAMP factor, which enlarges the area of hemolysis formed by Staphylococcus aureus when plated together on blood agar

79
Q

Streptococcus agalactiae (group B strep) is the number one cause of

A

neonatal meningitis

80
Q

Streptococcus agalactiae (group B strep) is the most common cause of

A

neonatal sepsis

81
Q

Streptococcus agalactiae can cause

A

pneumonia (primarily in infants)

82
Q

a positive CAMP test

A

a positive CAMP test appears as an “arrowhead” zone of hemolysis that forms at the point of intersection between Streptococcus agalactiae and Staphylococcus aureus

83
Q

pregnant women are screened for

A

Streptococcus agalactiae (group B strep) at 35-37 weeks of gestation, as GBS is the most common cause of neonatal meningitis

84
Q

pregnant women who test positive for Streptococcus agalactiae (group B strep) on screening at 35-37 weeks of gestation are given

A

intrapartum penicillin intravenously

85
Q

Streptococcus pneumoniae and viridans group streptococci are

A
  1. gram-positive cocci

2. alpha-hemolytic

86
Q

Alpha hemolytic means

A

able to partially breakdown hemoglobin

87
Q

Streptococcus pneumoniae is

A
  1. encapsulated
  2. susceptible to optochin
  3. lancet shaped
  4. diplococci
  5. bile soluble
88
Q

Streptococcus viridans group streptococci are

A
  1. non-encapsulated

2. optochin resistant

89
Q

Optochin

A

a chemical used in identification of alpha-hemolytic streptococci

90
Q

Bile soluble

A

no hydrolyzation of esculin → no growth in the presence of bile salts

91
Q

Streptococcus pneumoniae can cause

A

lobar pneumonia (usually with unilobar consolidation) with production of “rust-colored” sputum

92
Q

Streptococcus pneumoniae is the most common cause of

A

meningitis, otitis media, pneumonia, and sinusitis (MOPS)

93
Q

the IgA protease of Streptococcus pneumoniae

A

cleaves IgA at the hinge region → decreased effectiveness of IgA → bacterial adherence to mucosa

94
Q

sickle cell patients are more susceptible to infections from

A

encapsulated bacteria, such as Streptococcus pneumoniae

95
Q

_______ are effective against Streptococcus pneumoniae

A
  1. macrolides

2. ceftriaxone

96
Q

The pure polysaccharide vaccine against Streptococcus pneumoniae

A

produces a predominantly IgM (B-cell) response and can be administered to adults; children <2 years of age must be given the protein conjugated vaccine (polysaccharide conjugated with a carrier protein) to elicit an IgG (T-cell) response

97
Q

What kind of capsule does strep pnuemoniae have

A

polysaccharide capsule

98
Q

viridans group streptococci are able to grow in the presence of

A

bile salts (via hydrolyzation of esculin)

99
Q

Streptococcus mutans and sanguinis (viridans group streptococci) are

A

part of the normal flora of the mouth and play a role in tooth decay and the development of dental caries

100
Q

viridans group streptococci can

A
  1. adhere to previously damaged heart valves (most commonly the mitral valve) and establish infection, leading to subacute bacterial endocarditis
  2. adhere to tooth enamel and fibrin-platelet aggregates on damaged heart valves due to their ability to produce dextrans (insoluble extracellular polysaccharides) from sucrose substrate
  3. produce dextrans (insoluble extracellular polysaccharides) from sucrose substrate, which allows them to adhere to tooth enamel and fibrin-platelet aggregates on damages heart valves
101
Q

Enterococcus faecium and faecalis bacteria are

A
  1. gram positive cocci
  2. able to grow in 6.5% hypertonic saline
  3. able to grow in the presence of bile salts (via hydrolyzation of esculin)
102
Q

Enterococcus faecium is responsible for

A

the minority (10-15%) of enterococcal infections

103
Q

Enterococcus faecalis is responsible for

A

the majority (80-90%) of enterococcal infections

104
Q

Enterococcus faecium and faecalis can cause

A

a variety of infections, including UTIs (cystitis, pyelonephritis), endocarditis, and biliary tree infection

105
Q

some strains of Enterococcus faecium and faecalis have

A

developed resistance to multiple antibiotics, including vancomycin (vancomycin-resistant enterococci)

106
Q

linezolid and tigecycine can be used to treat

A

vancomycin-resistant enterococcal (VRE) infection

NBME Micro (36 decks)

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