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MLSCI 242 > LAB - Streptococci, Enterococci, and VRE > Flashcards

LAB - Streptococci, Enterococci, and VRE Flashcards

1
Q

Facultative organisms that are catalase-negative grow on the following media :

A

Streptococci; BAP, CAP, CNA, PEA

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2
Q

This gas is needed to support growth of some Strep species, while _________ environment tends to enhance hemolysis traits on BAP media

A

CO2, anaerobic

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3
Q

The most common cause of acute suppurative (pus-forming) bacterial pharyngitis or strep throat in children between 5 to 10

A

GAS (S. pyogenes)

  • not part of normal flora
  • followed by sequelae occasionally (acute rheumatic fever, acute glomerulonephritis)
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4
Q

Other common GAS infections

A

erysipelas, cellulitis, pyoderma

septicemia

toxic shock syndrome

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5
Q

Cause of serious neonatal sepsis and meningitis

A

GBS; S. agalactiae (usually occurs after vaginal delivery)

all pregnant women should be screened for GBS

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6
Q

Other infections GBS can cause in adults

A

UTIs, skin and soft tissue infections, and post-partum sepsis

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7
Q

Other serologic groups of beta-hemolytic strep

A

Lancefield’s groups C, G, and F
= less clinically significant
= more associated with normal flora of respiratory, GI tract, and vagina

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8
Q

most common cause of community-acquired bacterial pneumonia

A

S. pneumoniae (alpha hem)

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9
Q

Pneumococci

A
  • may be part of URT flora
  • may also be responsible for other pyogenic infections = pneumonia, acute bacterial meningitis, eye infections, infections of the middle ear
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10
Q

these have symptoms of “rusty sputum”

A

S. pneumoniae for bacterial penumonia

- due to blood-tinged aspirations

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11
Q

vaccine for S. pneumoniae

A

containing capsular serotype

- recommended for immunocompromised and elderly patients

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12
Q

Viridans group Strep

A
  • most normal inhabitants of mouth and URT
  • dental plaque, wound infections, brain abscesses
  • usually through rule out process of other strep or enterococci
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13
Q

Most frequent infection associated with viridans Strep

A

subacute bacterial endocarditis in patients with damaged or artificial heart valves

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14
Q

T or F. Enterococci belong t the same family as Streptococci

A

T!

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15
Q

Enterococci are normal inhabitants of the…

A

GI tract

- but also associated with UTI or wound infections

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16
Q

Enterococci hemolysis

A

non-hemolytic or alpha

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17
Q

These are frequently involved in infection following intensive antimicrobial treatment for infection with other bacteria = nosocomial acquired infections

A

Enterococci

18
Q

GDS

A
  • normal inhabitants of GI

- endocarditis and septicimia

19
Q

associated with colon cancer

A

GDS septicemia

20
Q

Why is it important to differentiate Enterococci from GDS

A

different antimicrobial resistance

21
Q

How do GDS and Enterococci differ?

A

heat resistance (60C)
ability to grow in presence of 6.5% NaCl
resistance to beta-lactam antibiotics and aminoglycosides

22
Q

Group A strep may be further subdivided into ~80 different serotypes on the basis of…

A

m protein = type-specific cell wall protein antigens

- epidemiological

23
Q

How do we ‘type’ Pneumococci

A
  • no group-specific cell wall carb antigen; most are encapsulated
  • serotype basis of type-specific capsular polysaccharide = Neufeld Quellung method
  • positive = swollen capsule surrounding blue-stained pneumo
  • commercial latex agg. test kits
24
Q

Two useful antibody determinations in evaluation of patients with recent streptococcal disease

A 
antistreptolysin O (ASO)
antideoxyribonuclease B (ADN-B)

streptolysin O and DNAse B produced by group A strep

endpoint = highest dilution of serum which neutralizes Streptolysin O and prevents hemolysis of RBC
- ASO titre elevated in ~85% of ARF patients

25
Q

oxygen labile hemolysin

A

streptolysin O
-so cultures for isolation of streptococci should be incubated anaerobically or at least a portion of culture under a reduced oxygen atmosphere

26
Q

Chaining will be less evident if…

A

smears are prepared from solid media (compared to broth cultures)

27
Q

pseudocatalase

A

weak pos reaction to catalase test by enterococci

28
Q

Cultures on BAP CO2

A

viridans and S. pneumoniae

29
Q

Bacitracin test

A

GAS = susceptible (any zone of inhibition)
GBS = resistant
- false positives with group C and G
- SXT discs inhibitory to most strep except group A and B

30
Q

CAMP factor

A
  • produced by GBS
  • enhances beta-lysin pf Staph aureus
  • arrowhead of beta-lysis
  • only positive for GBS
31
Q

T or F. GBS able to grow in 6.5% salt broth

A

T! but do not hydrolyze esculin

32
Q

Principle of 6.5% NaCl Broth

A

high salt conctn only allows salt-tolerant organisms like enteroccoci to grow
- pos = growth or GREEN/YELLOW (from purple)

33
Q

PYR hydrolysis

A
  • pos or GAS and Enterococcus sp.
  • hydrolyze PYR (L-pyrrolidonyl-beta-naphthylamide)
  • hydrolysis of substrate by pyrridonyl peptidase = B-naphthylamide free
  • B-naphthylamide becomes red after PYR reagent (cinnanaldehyde)
  • ten mins for hydrolysis (disc + bacteria; THEN reagent)
34
Q

In most clinical labs, only these two tests are set up to differentiate between Enterococcus sp. and S. bovis

A

BE and NaCl

35
Q

Two types of vancomycin resistance in Enterococci

A
  • intrinsic = E. gallinarum and casseliflavus; inherent, low-level resistance to van
  • acquired = clinically significant; E. faecalis and faecium; acquisition if genes from another; can pass on to other gram pos (vanA-E)
36
Q

Infected patients (VRE)

A

carry VRE; show clinical symptoms of disease

37
Q

Colonized patients (VRE)

A

carry VRE; no symptoms of infection

- usually GI or urinary tract

38
Q

Screening for VRE

A
  • info about potential sources = infection control measures
  • samples = peri-rectal/anal swabs or stool
    1. Bile Esculin Azide Screen
    2. VRE Screening Plates
39
Q

S. pneumo vs viridans colonies

A
  • S. pneumo has an autolytic enzyme that dissolves its own protoplasm = colonies dip down in center/flat compared to viridans
40
Q

Plate Bile Solubility

A
  • bile salt (sodium deoxycholate or taurocholate) accelrate autolytic enzyme activity by lowring surface tension of bacterial cell membrane
  • pos needs to be confirmed with Optochin = S. pneumo
41
Q

Optochin susceptibility

A
  • Pneumococci inhibited by optochin reagent (part of P disc)

- zone of inhibition greater than 15 mm = susceptible

MLSCI 242 (39 decks)

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