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Phase 2 Block 1 > Gram Positive Cocci > Flashcards

Gram Positive Cocci Flashcards

1
Q

There are 5 factors to take into consideration when assessing a pt for infection

A

Epidemiology of pathogen
Patient risk factors
Pre-analytics (factors before a sample is analyzed)
Analytics (how the sample is analyzed)
Post-analytics (how the analysis is reported

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2
Q

Which analytics step has the highest rate of errors?

A

Pre-analytics; analytics and post-analytics are lab controlled while pre- is not

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3
Q

What is the most important pre-analytic factor for getting an accurate result?

A

Volume

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4
Q

What does gram staining help with?

A

Guides workup and tx

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5
Q

What are the 3 types of media used in analytics of bacteria?

A

Enriched
Selective
Differential

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6
Q

What are the 3 types of hemolysis patterns?

A

⍺
β
γ

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7
Q

What colour is the staining associated with ⍺ hemolysis staining pattern?

A

Greening

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8
Q

What colour is the staining associated with β hemolysis staining pattern?

A

Clearing around the colonies

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9
Q

What colour is the staining associated with γ hemolysis staining pattern?

A

No hemolysis

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10
Q

What 3 things are looked at in analytics of a blood agar plate?

A

Hemolysis patterns
Colour of colonies
Shape of colonies

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11
Q

What are the 4 testing methods for determining the type of bacteria?

A

Biochemical testing (manual or commercial MALDI-TOF)
Serology
PCR
Antimicrobial susceptibility testing

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12
Q

What determines the shape of a bacteria?

A

The shape of its cell wall determines if it’s coccus, rod, or spiral

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13
Q

What is the coagulase test?

A

Tests for the coagulase enzyme that bacteria use to form a fibrin capsule around themselves to avoid phagocytosis

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14
Q

Describe what a positive coagulase test looks like

A

Clotted or clumping is seen

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15
Q

Is S. Aureus part of normal flora?

A

Yes; skin and nasal cavity
This is the reason for doing MRSA nose swabs

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16
Q

What is virulence?

A

How pathogenic an organism is and is determined by various factors

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17
Q

What type of host-bacteria relationship does S. Aureus demonstrate? (Flora/colonizer, opportunistic, pathogen)

A

Opportunistic pathogens

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18
Q

This bacteria is a leading cause of bacteremia

A

S. Aureus

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19
Q

Describe the gram stain of S. Aureus

A

Gram (+), Coccoid, clusters of grapes

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20
Q

What media are used for identifying S. Aureus?

A

Blood agar and mannitol salt agar

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21
Q

Why is mannitol salt agar used for S. Aureus?

A

Selective and differential agar
Selective: high salt inhibits most other bacteria
Differential: fermentation of mannitol by S. Aureus —> ↓ pH —> colour change in agar

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22
Q

What is the hemolysis pattern of S. Aureus?

A

Β-hemolytic; white-gold

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23
Q

What biochemical tests are positive for S. Aureus? (Catalase, coagulase slide, coagulase tube)

A

Catalase POS
Coagulase slide POS
Coagulase tube POS

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24
Q

What is the minimum inhibitory concentration?

A

Lowest drug concentration needed to inhibit visible growth of colonies

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25
Q

At least 90% of isolates of this bacteria make penicillinase

A

S. Aureus

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26
Q

This mobile genetic element —> MRSA

A

mecA

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27
Q

How does mecA create MRSA?

A

mecA is a genetic element that encodes PBP-2A protein that binds penicillins

28
Q

How are antibiotics selected for S. Aureus?

A

Abx therapy based on infection site, severity of infection, and probability of resistance

29
Q

What 4 groups of antibiotics is MRSA intrinsically resistant to?

A

β lactam combo drugs
Oral cephems
Most cephalosporins
Carbapenems

30
Q

What antibiotics is MRSA susceptible to?

A

Ceftaroline/Ceftobiprole (directly binds PBP-2a)
TMP-SMX, clindamycin, doxycycline, vanco, linezolid, daptomycin
Dapto is last resort

31
Q

Is S. Lugdunensis part of normal flora?

A

Yes; skin

32
Q

This bacteria causes infections similar to S. Aureus

A

S. Lugdunensis

33
Q

What are the differences in biochemical testing between S. Aureus and S. Lugdnensis?

A

S. aureus is positive in catalase and coagulase (tube and slide)
S. Lugdenensis is negative on coagulase tube

34
Q

What is S. Lugdnensis susceptible to?

A

β lactam combo drugs
Oral cephems
Most cephalosporins
Carbapenems
MSSA is also susceptible to these

35
Q

When is contamination of sample suspected instead of pathogen?

A

When 1/4 of bottles in blood culture yield a bacteria

36
Q

This bacteria is responsible for CA-UTIs commonly in 16-35F in late summer

A

S. Saprophyticus

37
Q

This enzyme allows S. Saprophyticus to invade the bladder wall

A

Urease

38
Q

What does a positive urease test look like?

A

Indicator (phenol red) turns from yellow-orange to pink-red

39
Q

That causes the colour change in the urease test?

A

Urease enzyme will break down urea into ammonia and CO2
Ammonia is alkaline —> indicator turning pink-red in response to alkaline env

40
Q

What is the treatment for S. Saprophyticus?

A

Nitrofuratoin, TMP-SMX, Cephalexin

41
Q

There are 2 β-hemolytic streptococci

A

Group A streptococci — S. Pyogenes
Group B streptococci — S. Agalactiae

42
Q

Streptococcus in this group show no hemolysis or ⍺-hemolysis

A

Viridans group strep

43
Q

What are some clinical diseases associated with group A strep?

A

Acute pharyngitis
Scarlet fever (exotoxin producing strains)
Acute rheumatic fever
Toxic shock syndrome
Skin infections (pyoderma, impetigo, cellulitis)
Necrotizing fasciitis (polymicrobial; GAS almost always present)

44
Q

Group A strep diagnostics?
Gram stain
Media
Morphology

A

Gram (+), coccoid pairs/chains
Blood agar media to grow
Β-hemolytic, white

45
Q

What is the first line therapy for Group A strep?

A

Penicillin (macrolide if allergic)

46
Q

What inhibits opsonization of group A strep?

A

M-protein

47
Q

Is Group A part of normal flora?

A

Yes; skin and throat
Like the S. Aureus of strep

48
Q

Is Group B strep part of normal flora?

A

Yes; GI and urogenital tract

49
Q

This bacteria is found colonizing in 30% of maternal urogenital tracts and has a 50% chance of transfer to the newborn

A

Group B strep

50
Q

How is transfer of maternal Group B strep to the newborn prevented?

A

Penicillin (macrolide if allergic) is given 24-48hrs before delivery to clear the GBS
Not permanent, GBS will re-establish

51
Q

How is screening for GBS done in pregnancy?

A

Rectal swab at 36-38 wks, placed into clear broth that turns orange if GBS is present

52
Q

List the bacteria for which AST is usually not done and are treated empirically instead

A

S. Saprophyticus
Group A Strep (S. Pyogenes)
Group B Strep (S. Agalactiae)

53
Q

This bacteria is the main cause of meningitis in people >3mo

A

S. Pneumoniae

54
Q

What are some clinical diseases are associated with S. Pneumoniae?

A

Meningitis
Otitis media
Sinusitis
Lower reps tract infection
Empyema

55
Q

This bacteria is the main cause of community acquired pneumonia

A

S. Pneumoniae

56
Q

This biochemical test can help determine with confidence that a suspected bacteria is S. Pneumoniae

A

Bile solubility - positive
This means the colony will lyse in a bile salt plate. May leave behind an imprint

57
Q

This bacteria has different breakpoints in MIC for dosing

A

S. Pneumoniae

58
Q

This bacteria is less virulent than S. Pneumoniae and can cause deep tissue abscesses. It is commonly seen with anaerobic bacteria

A

S. Anginosus

59
Q

What antibiotics are used for S. Anginosus?

A

Penicillin or Ceftriaxone

60
Q

What clinical diseases are associated with e. Faecium and e. Faecalis?

A

Bacteremia
Endocarditis
UTIs

61
Q

Enterococcus spp. have a lot of intrinsic resistances, which include:

A

Most cephalosporins
Β-lactams
Aminoglycosides
Clindamycin
Ertapenem
Septra

62
Q

95% of E. Faecalis is susceptible to this drug but <5% of e. Faecium are susceptible

A

Ampicillin

63
Q

What are the therapy options for e. Faecalis and e. faecium?

A

Synergistic β-lactams + aminoglycosides
Vanco
Cipro
Fosfomycin
Nitrofurantoin
Daptomycin
Linezolid

64
Q

What is the most common enterococci in clinical infections?

A

e. Faecalis

65
Q

Which enterococci is commonly associated with VRE?

A

e. Faecium

Phase 2 Block 1 (15 decks)

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