LAB - Streptococci, Enterococci, and VRE Flashcards
Facultative organisms that are catalase-negative grow on the following media :
Streptococci; BAP, CAP, CNA, PEA
This gas is needed to support growth of some Strep species, while _________ environment tends to enhance hemolysis traits on BAP media
CO2, anaerobic
The most common cause of acute suppurative (pus-forming) bacterial pharyngitis or strep throat in children between 5 to 10
GAS (S. pyogenes)
- not part of normal flora
- followed by sequelae occasionally (acute rheumatic fever, acute glomerulonephritis)
Other common GAS infections
erysipelas, cellulitis, pyoderma
septicemia
toxic shock syndrome
Cause of serious neonatal sepsis and meningitis
GBS; S. agalactiae (usually occurs after vaginal delivery)
all pregnant women should be screened for GBS
Other infections GBS can cause in adults
UTIs, skin and soft tissue infections, and post-partum sepsis
Other serologic groups of beta-hemolytic strep
Lancefield’s groups C, G, and F
= less clinically significant
= more associated with normal flora of respiratory, GI tract, and vagina
most common cause of community-acquired bacterial pneumonia
S. pneumoniae (alpha hem)
Pneumococci
- 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
these have symptoms of “rusty sputum”
S. pneumoniae for bacterial penumonia
- due to blood-tinged aspirations
vaccine for S. pneumoniae
containing capsular serotype
- recommended for immunocompromised and elderly patients
Viridans group Strep
- most normal inhabitants of mouth and URT
- dental plaque, wound infections, brain abscesses
- usually through rule out process of other strep or enterococci
Most frequent infection associated with viridans Strep
subacute bacterial endocarditis in patients with damaged or artificial heart valves
T or F. Enterococci belong t the same family as Streptococci
T!
Enterococci are normal inhabitants of the…
GI tract
- but also associated with UTI or wound infections
Enterococci hemolysis
non-hemolytic or alpha
These are frequently involved in infection following intensive antimicrobial treatment for infection with other bacteria = nosocomial acquired infections
Enterococci
GDS
- normal inhabitants of GI
- endocarditis and septicimia
associated with colon cancer
GDS septicemia
Why is it important to differentiate Enterococci from GDS
different antimicrobial resistance
How do GDS and Enterococci differ?
heat resistance (60C)
ability to grow in presence of 6.5% NaCl
resistance to beta-lactam antibiotics and aminoglycosides
Group A strep may be further subdivided into ~80 different serotypes on the basis of…
m protein = type-specific cell wall protein antigens
- epidemiological
How do we ‘type’ Pneumococci
- 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
Two useful antibody determinations in evaluation of patients with recent streptococcal disease
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
oxygen labile hemolysin
streptolysin O
-so cultures for isolation of streptococci should be incubated anaerobically or at least a portion of culture under a reduced oxygen atmosphere
Chaining will be less evident if…
smears are prepared from solid media (compared to broth cultures)
pseudocatalase
weak pos reaction to catalase test by enterococci
Cultures on BAP CO2
viridans and S. pneumoniae
Bacitracin test
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
CAMP factor
- produced by GBS
- enhances beta-lysin pf Staph aureus
- arrowhead of beta-lysis
- only positive for GBS
T or F. GBS able to grow in 6.5% salt broth
T! but do not hydrolyze esculin
Principle of 6.5% NaCl Broth
high salt conctn only allows salt-tolerant organisms like enteroccoci to grow
- pos = growth or GREEN/YELLOW (from purple)
PYR hydrolysis
- 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)
In most clinical labs, only these two tests are set up to differentiate between Enterococcus sp. and S. bovis
BE and NaCl
Two types of vancomycin resistance in Enterococci
- 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)
Infected patients (VRE)
carry VRE; show clinical symptoms of disease
Colonized patients (VRE)
carry VRE; no symptoms of infection
- usually GI or urinary tract
Screening for VRE
- info about potential sources = infection control measures
- samples = peri-rectal/anal swabs or stool
1. Bile Esculin Azide Screen
2. VRE Screening Plates
S. pneumo vs viridans colonies
- S. pneumo has an autolytic enzyme that dissolves its own protoplasm = colonies dip down in center/flat compared to viridans
Plate Bile Solubility
- 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
Optochin susceptibility
- Pneumococci inhibited by optochin reagent (part of P disc)
- zone of inhibition greater than 15 mm = susceptible
