LAB - Streptococci, Enterococci, and VRE

Question 1

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

Answer 1

Streptococci; BAP, CAP, CNA, PEA

Question 2

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

Answer 2

CO2, anaerobic

Question 3

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

Answer 3

GAS (S. pyogenes)

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

Question 4

Other common GAS infections

Answer 4

erysipelas, cellulitis, pyoderma

septicemia

toxic shock syndrome

Question 5

Cause of serious neonatal sepsis and meningitis

Answer 5

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

all pregnant women should be screened for GBS

Question 6

Other infections GBS can cause in adults

Answer 6

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

Question 7

Other serologic groups of beta-hemolytic strep

Answer 7

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

Question 8

most common cause of community-acquired bacterial pneumonia

Answer 8

S. pneumoniae (alpha hem)

Question 9

Pneumococci

Answer 9

• 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

Question 10

these have symptoms of “rusty sputum”

Answer 10

S. pneumoniae for bacterial penumonia

- due to blood-tinged aspirations

Question 11

vaccine for S. pneumoniae

Answer 11

containing capsular serotype

- recommended for immunocompromised and elderly patients

Question 12

Viridans group Strep

Answer 12

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

Question 13

Most frequent infection associated with viridans Strep

Answer 13

subacute bacterial endocarditis in patients with damaged or artificial heart valves

Question 14

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

Answer 14

T!

Question 15

Enterococci are normal inhabitants of the…

Answer 15

GI tract

- but also associated with UTI or wound infections

Question 16

Enterococci hemolysis

Answer 16

non-hemolytic or alpha

Question 17

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

Answer 17

Enterococci

Question 18

GDS

Answer 18

• normal inhabitants of GI

- endocarditis and septicimia

Question 19

associated with colon cancer

Answer 19

GDS septicemia

Question 20

Why is it important to differentiate Enterococci from GDS

Answer 20

different antimicrobial resistance

Question 21

How do GDS and Enterococci differ?

Answer 21

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

Question 22

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

Answer 22

m protein = type-specific cell wall protein antigens

- epidemiological

Question 23

How do we ‘type’ Pneumococci

Answer 23

• 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

Question 24

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

Answer 24

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

Question 25

oxygen labile hemolysin

Answer 25

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

Question 26

Chaining will be less evident if...

Answer 26

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

Question 27

pseudocatalase

Answer 27

weak pos reaction to catalase test by enterococci

Question 28

Cultures on BAP CO2

Answer 28

viridans and S. pneumoniae

Question 29

Bacitracin test

Answer 29

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

Question 30

CAMP factor

Answer 30

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

Question 31

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

Answer 31

T! but do not hydrolyze esculin

Question 32

Principle of 6.5% NaCl Broth

Answer 32

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

Question 33

PYR hydrolysis

Answer 33

- 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)

Question 34

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

Answer 34

BE and NaCl

Question 35

Two types of vancomycin resistance in Enterococci

Answer 35

- 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)

Question 36

Infected patients (VRE)

Answer 36

carry VRE; show clinical symptoms of disease

Question 37

Colonized patients (VRE)

Answer 37

carry VRE; no symptoms of infection | - usually GI or urinary tract

Question 38

Screening for VRE

Answer 38

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

Question 39

S. pneumo vs viridans colonies

Answer 39

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

Question 40

Plate Bile Solubility

Answer 40

- 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

Question 41

Optochin susceptibility

Answer 41

- Pneumococci inhibited by optochin reagent (part of P disc) | - zone of inhibition greater than 15 mm = susceptible