Exam2Lec2StaphandStrep Flashcards
What are the microbiological properties of Staphylocci
gram positive cocci
single, pairs, short chains
most common: clusters
Facultative anaerobes
What are the three major species of Staphylocci?
Staphylococcus aureus
Staphylococcus epidermis
Staphylococcus saphrophyticus
What does protein A do?
binds FC region of IgG molecule
What do Teichoic acids do?
binds fibronectin on mucosal surfaces
What does leukocidin cause?
Call lysis then tissue destruction and abscess formation
What are the 5 virulence factors of S. aureus?
- Leukocidin
- Protein A
- Teichoic Acids
- Coagulase
- Hemolysins
What are the virulence factors of s. aureus that causes toxin-mediated disease? (and be specific as to what they cause)
Enterotoxins cause food poisoning
Exfoliative toxin causes SSSS
Toxic Shock Syndrome Toxin 1 causes Toxic Shock Syndrome
Panton Valentine Leukocidin (PVL) causes Necrotic Lesions involving skin and mucosa
What exactly are enterotoxins?
acid and heat resistant toxins that causes food poisoning
occurs 1-8 hours after toxin ingestion
short < 24 hours
What exactly are exfoliative toxin (exfoliatin) unique to s aureus?
toxin which causes staphylococcal scalded skin syndrome
erythema followed by desquamation
sloughing of outermost layer of skin
primarily occurs in infants
What exactly is toxic shock syndrome toxin (TSST1)
Toxin which causes hypotension, rash, desquamation, production of cytokines. Primarily occurs in women. Originally associated with tampon use.
What exactly is Penton-Valetine Leukocidin(PVL)?
PVL positive strains of S. aures are being found in increasing prevalence in community acquired MRSA.
Begins as skin infection and progresses toward a systemic infection w/ high mortality
severe soft bone and tissue infection, high chance of sepsis
Typically spread skin-to-skin contact and fomites
What are the two mechanisms of PVL?
- Opens up pores in cell membranes and leads to cell lysis
- entering cell and inducing apoptosis via capase cascade which leads to apoptosis
How can we distinguish between Staph and Strep?
Catalase test
Staph: catalase positive
Strep: catalase negative
How can we distinguish between the three major species of staph?
- Coagulase test
S. aureus= coagulase positive
S. epidermidis and S. saprophyticus= coagulase negative - Blood Agar Plate (BAP)
S. aureus= beta-hemolytic
S. epidermidis= non-hemolytic (gamma) - Mannitol Agar Culture
yellow: S. aureus
What does alpha, beta, and gamma hemolysis show? And what colors would they be?
Alpha: partial hemolysis (green/brown)
Beta: total hemolysis (clear)
Gamma: no hemolysis (no change)
How does mannitol salt agar work?
salt in agar kills off other types of bacteria except for staph
In mannitol salt agar, which type of staph will change color from pink to yellow via pH change?
s. aureus
What is the treatment for staph infections?
drainage of lesions
antibiotics (oxacillin, cephalosporin)
vancomycin for MRSA
note plasmid encoded beta lactamases common
What antibiotic is specifically used for MRSA?
Vancomycin
What are the microbiological properties of Streptococci?
gram positive cocci
pairs, short chains, long chains
NO CLUSTERS (this is staph)
Facultative Anaerobes
What are the three major species of Streptococci?
Streptococcus pyogenes
Streptococcus pneumoniae
Streptococcus agalactiae
Does Streptococcocus pnemoniae have a lancefield classification?
NO
What is the lancefield classifications? And which strep species is group a/b
It’s a classification system based on the carbohydrate composition of bacterial antigens found on their cell walls.
Group A= streptococcus pyogenes
Group B= streptococcus agalactiae
What are the Strep. pyogenes virulence factors?
- Streptolysins (hemolysins)
- Erthrogenic Toxin
- Exotoxin A
- Exotoxin B
- Capsule (some)
- M protein (all)
- Protein F
- Protein G (equivalent of protein A)
- C-Polysaccharide
What is the typical age range and asymptomatic carrier rate for respiratory infections for strep pyogenes?
5-15 years old, 5% (usually adults)
The epidemiology of group A infections of strep include skin infections which is contamination of abrasion. How is this spread and what is the age range of patients?
direct contact or shared fomites
patients 2-5 years old.
What is the pathogenesis of respiratory infections for strep pyogenes?
- Organisms inhaled (aerosols) and binds to epithelium via F protein
- Produces M protein: inhibits phagocytosis and complement
- Steptolyosin damages epithelial tissue
What are the suppurative (pus-producing) diseases of Strep pyogenes?
Pharyngitis, scarlet fever, streptococcal toxic shock, cellulitis, necrotizing fascitis
What are the non- suppurative (non-pus producing) diseases of Strep pyogenes?
rheumatic fever
glomerulonephrils
What is pharyngitis (strep throat) and its virulence factor?
presents as: sore throat, fever, malaise, headache
develops 2-4 days after exposure
virulence factor: streptolysin
What is scarlet fever and its virulence factor?
presents as: strawberry tongue, diffuse rash, fever
virulence factor: erythrogenic toxin (superantigen)
Lysogenic phage encodes pyrogenic exotoxin
exotoxin spreads through circulatory system
What is acute glomerulonephritis?
presents as: edema, hypertension, proteinuria, hematuria
Occurs 10 days following infection
Involved deposition of antigen-antibody complexes in the kidneys
Which disease involved the deposition of antigen-antibody complexes in the kidneys (Type III hypersensitivity)
Acute Glomerulonephritis
What does virulence factor M proteins entail?
Involves inflammatory response to streptococcal antigens. Can lead to chronic, progressive heart damage.
What is rheumatic fever and its virulence factor?
presents as: fever, carditis, polyarthritis
occurs 3 weeks following pharyngitis
Virulence factor: M protein
Exotoxin B is associated with
necrotizing fascitis
Exotoxin A is associated with
toxic shock syndrome
What are the three virulence factors for strep agalactiae?
Capsule, cell wall, enzymes
Which parts of the capsule are the virulence factor for strep agalactiae?
Sialic acids, galactose, glucose, glucosamine
Which parts of the cell wall are the virulence factor for strep agalactiae?
group B specific carbohydrate, lipoteichoic acids
Which enzymes are the virulence factor for strep agalactiae?
deoxyribonuclease, hyaluronidase, neuroaminidase, proteases, hemolysin
S. agalactiae presents as what?
neonatal infections
1. puerperal sepsis
2. septicemia
3. pneumonia
4. meningitis
Which strep is specific for neonatal infections?
strep agalactiae
What is the laboratory diagnosis for S. agalactiae (group B)?
- beta hemolytic
large colonies
small hemolytic - Bacitracin resistant
What is the laboratory diagnosis for S. pyogenes (group A)?
- Beta-hemolytic-small (1-2) white colonies, Large hemolytic area
- Bacitracin sensitive
- Rapid test (group A carbohydrate antigen detection)
The most common presentation of strep agalactiae (GroupB) is caused by transmission from what?
Mother to child during vaginal delivery
What is the microbiological properties for S. pneumoniae?
oval/lancet shaped
diplococci (pairs)
What are the virulence factors for s. pneumoniae?
capsule
What are clinical diseases associated with S. pneumoniae?
pneumonia, sinusitis, otitis media, bacteremia, meningitis
What is the lab diagnosis for S. pneumoniae?
alpha hemolytic
Is the mannitol salt agar differential, specific, both, or neither
both
A 7 year old girl refuses to go to school because she is tired and cranky. By lunchtime, she was not hungry and had a fever and complained of a sore throat. The mother took her to the pediatrician where her temperature was noted to be 39.6 degrees Celsius. The pediatrician observed her throat to be red with a gray-ish white exudate on both tonsils. Her cervical lymph nodes were enlarges and tender, The infection was diagnosed by a rapid immunoassay and confirmed by culture and identification.
Upon confirmatory laboratory testing, which
of the following results would you expect for
this patient’s isolate?
A. Beta-hemolytic, Gram positive cocci in chains,
bacitracin sensitive
B.Beta-hemolytic, Gram-positive cocci in chains,
bacitracin resistant
C. Alpha-hemolytic, Gram-positive cocci in
clusters, Catalase positive, coagulase positive
D. Alpha-hemolytic, Gram-positive cocci in pairs,
catalase negative
E. Gamma-hemolytic, Gram-positive cocci in
clusters, catalase positive
a
A 60 year-old alcoholic abruptly develops shaking
chills, cough, and severe pain on the right side of
his chest. He has a high fever – 104 F and he is
breathing in a shallow manner to limit the pain.
His cough is characterized by rust colored sputum.
Gram staining shows many pmns and lancet-
shaped gram-positive diplococci and blood
cultures and sputum cultures were grew alpha-
hemolytic colonies.
Which is an important virulence factor for the disease-causing bacterium from this case?
A. Protein A
B. Polysaccharide capsule
C. Panton-Valentine leukocidin
D. Lipopolysaccharide
E. Protein B
b
Which of the following characteristics is unique to Staphylococci in comparison to
Streptococci?
A. Gram+
B. Facultative Anaerobe
C. Short Chains
D. Catalase+
d
Which S. aureus toxin is responsible for the formation of pores in epithelial cells thus
leading to lysis?
A. alpha toxin
B. Enterotoxins
C. Toxic Shock Syndrome Toxin-1
D. Exfoliative Toxin
a
Which of the following is not a considered a suppurative disease?
A. Cellulitis
B. Pharyngitis
C. Rheumatic Fever
D. Streptococcal Toxic Shock
c
Which of the following is not a common clinical indicator of scarlet fever?
A. Diffuse rash
B. Strawberry tongue
C. Pharyngitis
D. Carditis
d
Streptococcus agalactiae is most likely to cause which of the following conditions?
A. Glomerulonephritis
B. Newborn Meningitis
C. Rheumatic Fever
D. Necrotizing Fasciitis
b
An outbreak of sepsis caused by Staphylococcus aureus has occurred in the newborn nursery. You are called upon to investigate. According to your knowledge of the normal flora, what is the MOST likely source of the organism?
(A) Colon
(B) Nose
(C) Throat
(D) Vagina
b
A culture of skin lesions from a patient with pyoderma (impetigo) shows numerous colonies surrounded by a zone of β-hemolysis on a blood agar plate. A Gram-stained smear shows gram-positive cocci. If you found the catalase test to be negative, which one of the following organisms would you MOST probably have
isolated?
(A) Streptococcus pyogenes
(B) Staphylococcus aureus
(C) Staphylococcus epidermidis
(D) Streptococcus pneumoniae
a
The coagulase test, in which the bacteria cause plasma to clot, is used to distinguish:
(A) Streptococcus pyogenes from Enterococcus faecalis
(B) Streptococcus pyogenes from Staphylococcus aureus
(C) Staphylococcus aureus from Staphylococcus epidermidis
(D) Staphylococcus epidermidis from Neisseria meningitidis
c
Which one of the following is a virulence factor for Staphylococcus aureus?
(A) A heat-labile toxin that inhibits glycine release at the internuncial neuron
(B) An oxygen-labile hemolysin
(C) Resistance to novobiocin
(D) Protein A that binds to the Fc portion of IgG
d
Acute glomerulonephritis is a nonsuppurative complication that follows infection by which one of the following organisms?
(A) Enterococcus faecalis
(B) Streptococcus pyogenes
(C) Streptococcus pneumoniae
(D) Streptococcus agalactiae
b
Which one of the following is NOT a characteristic of the
Staphylococcus associated with toxic shock syndrome?
(A) Release of a superantigen
(B) Coagulase production
(C) Appearance of the organism in grapelike clusters on Gram-stained smear
(D) Catalase-negative reaction
d
Which one of the following is NOT an important characteristic of Streptococcus pyogenes?
(A) Protein A
(B) M protein
(C) β-Hemolysin
(D) Polysaccharide group-specific substance
a
Each of the following is associated with the Lancefield group B streptococci (S. agalactiae) EXCEPT:
(A) Pyoderma (impetigo)
(B) Vaginal carriage in 5% to 25% of normal women of child-bearing age
(C) Neonatal sepsis and meningitis
(D) β-Hemolysis
a
Which one of the following organisms is the MOST frequent bacterial cause of pharyngitis?
(A) Staphylococcus aureus
(B) Streptococcus pneumoniae
(C) Streptococcus pyogenes
(D) Neisseria meningitidis
c
CASE: Your patient is a 15-year-old boy with migratory polyarthritis, fever, and a new, loud cardiac murmur. You make a clinical diagnosis of rheumatic fever. Which one of the following laboratory results is MOST likely to be found in this patient?
(A) A blood culture is positive for Streptococcus pyogenes at this time.
(B) A throat culture is positive for Streptococcus pyogenes at this time.
(C) A Gram stain of the joint fluid shows gram-positive cocci in chains at this time.
(D) An anti-streptolysin O assay is positive at this time.
d
CASE: Your patient is a 15-year-old boy with migratory polyarthritis, fever, and a new, loud cardiac murmur. You make a clinical diagnosis of rheumatic fever.
Which one of the following modes of pathogenesis is MOST compatible with a diagnosis of rheumatic fever?
(A) Bacteria attach to joint and heart tissue via pili, invade, and cause inflammation.
(B) Bacteria secrete exotoxins that circulate via the blood to the joints and heart.
(C) Bacterial antigens induce antibodies that cross-react with joint and heart tissue.
(D) Bacterial endotoxin induces interleukin-1 and tumor necrosis factor, which cause inflammation in joint and heart tissue.
c
CASE: Your patient is a 15-year-old boy with migratory polyarthritis, fever, and a new, loud cardiac murmur. You make a clinical diagnosis of rheumatic fever. Which one of the following approaches is MOST likely to prevent endocarditis in patients with rheumatic fever?
(A) They should take the streptococcal polysaccharide vaccine.
(B) They should take penicillin if they have dental surgery.
(C) They should take the toxoid vaccine every 5 years.
(D) They should take rifampin if they have abdominal surgery.
b
CASE: Your patient is a 10-year-old girl who has leukemia and is receiving chemotherapy through an indwelling venous catheter. She now has a fever of 39°C but is otherwise asymptomatic. You do a blood culture, and the laboratory reports growth of Staphylococcus epidermidis. Which one of the following results is LEAST likely to be found by the clinical laboratory?
(A) Gram-positive cocci in clusters were seen on Gram stain of
the blood culture.
(B) Subculture of the blood culture onto blood agar revealed
nonhemolytic colonies.
(C) A coagulase test on the colonies was negative.
(D) A catalase test on the colonies was negative.
d
CASE: Your patient is a 3-year-old girl with fever and pain in her right ear. On physical examination, the drum is found to be perforated, and a bloody exudate is seen. A Gram stain of the exudate reveals gram-positive diplococci.
623. Of the following, which one is the MOST likely cause?
(A) Streptococcus pyogenes
(B) Staphylococcus aureus
(C) Corynebacterium diphtheriae
(D) Streptococcus pneumoniae
d
CASE: You do a throat culture, and many small, translucent colonies that are β-hemolytic grow on blood agar. Gram stain of one of these colonies
reveals gram-positive cocci in chains. Of the following, which one is the MOST likely organism to
cause this infection?
(A) Streptococcus pneumoniae
(B) Streptococcus pyogenes
(C) Streptococcus agalactiae (group B Streptococcus)
(D) Peptostreptococcus species
b
CASE: Your patient is a 6-year-old boy with papular and pustular skin lesions on his face. A serous, “honey-colored” fluid exudes from the lesions. You suspect impetigo. A Gram stain of the pus reveals many neutrophils and gram-positive cocci in chains.f you cultured the pus on blood agar, which one of the following
would you be MOST likely to see?
(A) Small β-hemolytic colonies containing bacteria that are
bacitracin-sensitive
(B) Small α-hemolytic colonies containing bacteria that are resistant to optochin
(C) Large nonhemolytic colonies containing bacteria that are oxidase-positive
(D) Small nonhemolytic colonies containing bacteria that grow in 6.5% NaCl
a
