Gram-positive cocci Flashcards
What lab findings are useful to help diagnose Strep. pneumoniae?
spinal tap cloudy w/ increase in PMNs and low glucose
lancet-shaped gram+ cocci
alpha-hemolytic on blood agar
inhibited by optochin
older cells may appear gram-
lysed by bile
Identify the major virulence/toxicity factor associated with Staph. saprophyticus.
novobiocin resistant
How is Strep. agalactiae (group B strep) transmitted?
during childbirth from mother to infant
Identify the major virulence/toxicity factor associated with Strep. viridans.
destran biofilm-mediated adhesion to teeth and heart valves
What is the morphology of Group D Strep./Enterococcus?
cocci
Name some pyogenic manifestations of Strep. pyogenes.
pharyngitis, cellulitis, impetigo
When do you test for bacitracin sensitivity or resisitance?
to distinguish beta-hemolytic strep.
bacitracin-sensitive suggests GABHS (strep. pyogenes)
bacitracin-resistant suggests GBBHS (strep. agalactiae)
What organisms are beta hemolytic?
Staph. aureus, Strep. pyogenes, Strep. agalactiae, Lysteria monocytogenes
Identify the major virulence/toxicity factors associated with Strep. pyogenes (GABHS).
erythrogenic toxin may lead to scarlet fever which can progress to rheumatic fever
hyaluronic acid capsule in non-immunogenic, inhibiting phagoctyic uptake
M-protein is antiphagocytic
M12 strains associated with acute glomerulonephritis
Staph. aureus is catalase __ and coagulase __.
+
+
Viridans strep are catalase __ and optochin __.
sensitive
resistant
How does Strep. agalactiae gram stain?
+
T/F: enterococci (group D strep.) are penicillin G sensitive and show variable hemolysis
F - they are resistant but do have variable hemolysis
What is the “most common” associated with Strep. agalactiae?
neonatal sepsis and meningitis
What are catalase and coagulase tests used for?
Catalase is used to distinguish staph (+) from strep (-)
Coagulase is used to distinguish S. aureus (+) from S. epidermis and S. saprophyticus (-)
How does Strep. pneumoniae gram stain?
+
What is the morphology of Strep. pneumoniae?
cocci
What lab findings are useful to help diagnose Staph. saprophyticus?
+ growth on blood agar
+ catalase
+ gamma hemolysis
+ novobiocin resistance
Strep. pyogenes is catalase __ and bacitracin __.
negative
sensitive
What is the second leading cause of UTIs in sexually active women?
Staph. saprophyticus
What are the clinical manifestations of Strep. pneumoniae?
pneumonia, meningitis, bacteremia, OM, sinusitis
What lab findings are useful to help diagnose Staph. epidermidis?
gram + cocci arranged in clusters
catalase +
coagulase -
no hemolysis
What is the “most common” associated with Strep. pneumoniae?
bacterial pneumonia in adults
meningitis
What lab findings are useful to help diagnose Strep. pyogenes?
beta hemolysis +
susceptible to bacitracin
rapid antigen strep test
gram + cocci in chains
catalase -
ASO titer for rheumatic fever
Does Staph. aureus gram stain positive or negative?
+
Staph. aureus: TSST is a superantigen that binds to __ and __ receptors. This causes __ of T cells, leading to toxic shock syndrome.
MHC II
T-cell receptors
polyclonal activation of T-cells
What is the major reservoir for Strep. agalactiae?
normal flora of female genital tract
GI tract
What is the morphology of Strep. pyogenes?
cocci in chains or pairs
Name some key lab findings that are useful to help diagnose Staph. aureus.
gram+
yellow, grape-like clusters on blood agar
beta-hemolytic
catalase +
coagulase +
salt tolerant
ferments mannitol (s. epidermidis cannot)
Facultative anaerobe
Identify the major virulence/toxicity factors associated with Strep. agalactiae.
penicillin resistant
encapsulated
beta-hemolysin
CAMP factor
List the SSx of rheumatic fever.
polyarthritis, erythema marginatum, chorea, carditis, subQ nodules
Identify the major virulence/toxicity factor associated with Strep. pneumoniae.
can make over 85 antigenically distinct capsular polysaccharides, which can interfere with phagocytosis.
Identify four major virulence/toxicity factors associated with Staph. aureus.
protein A inhibits phagocytosis, binds Fc portion of antibody
- Bind Fc region on IgG → ↓ Complement activation → ↓ C3b
enterotoxins A-E are heat stable
TSST-1 causes TSS
coagulases convert fibrinogen to a fibrin clot
exfoliatins cause scalded skin syndrome
What is the morphology of Staph. epidermidis?
cocci
Strep. pneumococci are catalase __ and optochin __.
-
sensitive
What are the “most commons” associated with Strep. pyogenes?
pharyngitis
cellulitis
erysipelas in children
What are the clinical manifestations of Strep. agalactiae?
acute lower UTI (uncommon)
neonatal pneumonia
sepsis
meningitis
What is the morphology of Staph. saprophyticus?
cocci
What are the clinical manifestations of Staph. saprophyticus?
UTIs, esp. in young sexually active women
Sx: dysuria, hematuria, frequent urination, burning urination and urgency
What lab findings are useful to help diagnose Strep. viridans?
alpha-hemolytic
resistant to optochin
gram+ cocci in chains
bile resistant
Staph. aureus: What is the function of protein A?
virulence factor - binds to Fc-IgG and inhibits complement fixation and phagocytosis
How is Strep. pneumoniae transmitted?
respiratory drops
Does Staph. aureus ferment lactose?
no
T/F: S. aurues causes skin disease and organ abscesses, but not pneumonia
F - causes all 3
How does Staph. saprophyticus gram stain?
+
What are the pyogenic, immunologic and toxigenic clinical manifestations of Strep. pyogenes?
pyogenic (pharyngitis, impetigo, cellulitis, erysipelas)
immunogenic (glomerulonephritis, erythema nodosum, rheumatic fever, rheumatic heart disease)
toxigenic (scarlet fever, purperal fever)
Identify the major virulence/toxicity factors associated with Staph. epidermidis.
highly antibiotic resistant (PSM peptide toxin)
can form biofilm and adhere to surfaces like catheters
What is the major reservoir for Strep. pneumoniae?
human upper respiratory tract
How does Strep. viridans gram stain?
+
What are the clinical manifestations of Staph. epidermidis?
prosthetic, surgical and wound infections (nosocomial) especially in the immunocompromised patient
inflammation at site of infection, fever, fatigue
How does Staph. epidermidis gram stain?
+
Viridans strep are __ hemolytic
alpha
Identify relevant epidemiology and risk factors associated with Staph. aureus.
surgery or any break in the skin
severe neutropenia
IV drug abuse
chronic granulomatous disease
How is Staph. aureus transmitted?
hands and sneezing
surgical wounds
contaminated foods, esp. home canned meats, potato salad
Name three toxins of S. aureus and a syndrome caused by each.
TSST-1 (TSS)
exofoliative toxin (scalded skin syndrome)
enterotoxins (rapid onset food poisoning)
How does group D Strep/enterococcus gram stain?
+
What lab findings are useful to help diagnose Strep. agalactiae?
catalase -
beta-hemolytic on blood agar
bacitraicin resistant
CAMP+ (indicates group B)
hydrolyzes hippurate
What organisms are alpha-hemolytic?
strep. pneumoniae
strep. viridans
T/F: S. aureus causes acute bacterial endocarditis.
T
Strep agalactiae is catalase __ and bacitracin __.
-
resistant
What are the clinical manifestations of group D strep/enterococcus?
URI (rare, but severe in immunocompromised, esp. following GI surgery)
sepsis dt contaminated needle use (rare).
How does Staph. aureus cause toxic shock syndrome?
The toxin is a superantigen that binds to MHC II protein and T-cell receptors and induces IL-1 and IL-2, causing TSS
T/F: S. aureus food poisoning is due to bacterial infiltration of the intestinal wall.
F, dt ingestion of preformed enterotoxin
What are the clinical manifestations of Strep. viridans?
opportunistic infections of heart valves, blood, skin or wounds
Strep. mutans causes dental caries.
Identify relevant epidemiology and risk factors associated with Strep. pneumoniae.
individuals with depressed cough reflex or damaged mucociliary elevator
pulmonary circulation problems
splenectomy
head trauma
alcoholism
sickle cell anemia
What is the morphology of Strep. viridans?
cocci
How is Strep. pyogenes transmitted?
respiratory droplets
direct contact with skin
direct contact with objects.
How is Strep. viridans transmitted?
usually already present in host
dental work may expose organism to heart valves which, if damaged, may become infected
What lab findings are useful to help diagnose group D strep/enterococcus?
mostly alpha- or non-hemolytic
resistant to bile salts
Name the bacteria that produces a yellow pigment.
S. aureus
What is the morphology of Staph. aureus?
cocci
Which are not toxigenic manifestations of Strep. pyogenes: scarlet fever, rheumatic fever, TSS, acute glomerulonephritis.
rheumatic fever and acute glomerulonephritis are immune-mediated manifestations
How do you differentiate Strep. viridans from Strep. pneumoniae in the lab?
both are alpha-hemolytic, but viridans strep is resistant to optochin
What is the major reservoir for Strep. pyogenes?
human throat and skin
Name nine clinical manifestations of Staph. aureus.
impetigo
gastroenteritis
infective endocarditis
abscesses and mastitis
TSS
pneumonia
surgical infections
osteomyelitis
necrotizing fasciitis
One hour after eating custard at a picnic, the whole family vomits. After 10 hours all are better. Organism?
S. aureus (produces preformed enterotoxin)
Does Strep. pyogenes gram stain positive or negative?
+
What is the morphology of Strep. agalactiae?
cocci
Which of the following agar media is most selective for Staphylococcus aureus?
Mannitol salt agar is a selective medium for Staphylococcus aureus.
Mannitol is a carbohydrate that is fermented by S. aureus, leading to acid production and a change in the color of the agar.
examples of beta-hemolytic gram + cocci microbes.
Staphylococcus aureus, Streptococcus pyogenes, and Streptococcus agalactiae
Which 2 staphs are novobiocin sensitive?
s. Epidermidis
s. Aureus
Food most assoc. w/ s. aureus gastroenteritis?
Dairy
S. aureus exfoliative toxin cleaves _____
desmoglein 1, leading to scalded skin syndrome
Nikolsky sign on infants
necrotizing fasciitis is caused by ____ , an endo/exo toxin secreted by s. aureus
Panton-Valentine leukocidin is an exotoxin secreted by S. aureus.
In the setting of infectious parotitis, serum amylase will be ___while serum lipase will be ___
elevated
normal
bacterial endocarditis affects which valve first?
Two other signs
Risk factor?
Tricuspid valve - tricuspid regurg
Splinter hemorrhages, Osler nodes
IV drug use
S. aureus osteomyelitis most commonly affects which bone in adults? Children?
Adults - vertebrae
Children - long bones/femur
In diabetics- fist metatarsal
what does the mec gene encode for?
How does s. aureus acquire it?
PBP-2A is encoded by the mec gene and provides resistance to β-lactam antibiotics.
(Penicillin binding protein)
Acquired via transduction, a form of horizontal gene transfer in which viral bacteriophages transfer bacterial DNA from one bacteria to another.
S. epidermidis infections are most commonly associated with
Central lines/ foreign body infections
Urinalysis in S. saprophyticus UTI will show
+ WBCs,
positive leukocyte esterase,
and negative nitrites.
OVRPS a
Optochin sensitivity
Viridans - resistant
s. Pneumonia - sensitive
Alpha hemolytic
B-BRAS
Basitracin sensitivity
Group B (agalactiae) - resistant
Group A (pyogenes) - sensitive
S. pneumoniae have the ability to cleave which immunoglobulin?
IgA, allows it to invade the mucosa
S. sanguinis is the most associated with
bacterial endocarditis after dental procedures.
Toxin assoc. w/ s. pyogenes and function
Streptolysin O, highly antigenic exotoxin that degrades cell membranes
JONES ->
what disease?
causative agent?
S. Pyogenes
RHeumatic fever
Joints - polyarthritis
O (<3) - carditis
Nodules - sub cu
Erythema rash
Sydenham Chorea
Also, ↑ ESR, fever
Common findings of scarlet fever
sandpaper-like maculopapular rash, strawberry tongue,
erysipelas vs. cellulits
erysipelas - well demarcated rash on lower limbs (possibly face)
cellulitis - not well demarcated, infection is deep in dermis. Streaking erythema towards lymph nodes
Which type of hypersensitivity response is acute rheumatic fever?
II
Which type of hypersensitivity response is poststreptococcal glomerulonephritis?
Explain
III, caused by deposition of antigen-immune complexes in basement membrane of glomerulus.
The capsule of s. agalactiae is made of
sialic acid polysaccharide capsule
Pregnant women are screened for S. agalactiae colonization at which point in gestation?
36 w
Neonatal meningitis is caused by:
Sings:
s. agalactiae
bulging fontanelle, lethargy, hypotonia, poor appetite, and thermoregulatory dysfunction
S. gallolyticus (previously named S. bovis)
type of hemolysis
causes
oxygen preference?
Gamma hemolysis
Bovis in blood = cancer in colon
facultative anaerobe
gallolyticus vs. enterococci
gallolyticus is PYR -
enterococci is PYR +
both are gamma-hemolytic
