Microbiology > Staphylococcus and Streptococcus > Flashcards

Staphylococcus and Streptococcus Flashcards

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1
Q

What is the morphology of staphylococcus species?

A

Gram positive cocci in clusters

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2
Q

What test differentiate staphylococcus from streptococcus?

A

Catalase test – Staphylococcus is catalase-positive.

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3
Q

Which staphylococcus species is coagulase positive

A

Staphylococcus Aueres

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4
Q

What type of hemolysis is usually seen with S. auerus on blood agar?

A

Beta hemolysis (clear zone)

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5
Q

What agar is selective and differential for staphylococus species?

A

Mannitol Salt Agar (MSA) – S. aureus ferments mannitol → yellow colonies.

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6
Q

What does the coagulase test detect

A

The ability to convert fibrinogen to fibrin

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7
Q

What distinguishes S. epidermidis from S. saprophyticus in the lab?

A

Novobiocin susceptibility:
S. epidermidis = sensitive
S. saprophyticus = resistant

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8
Q

Which Staphylococcus species is a common cause of UTIs in young women?

A

Staphylococcus saprophyticus

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9
Q

What virulence factor of S. aureus prevents phagocytosis?

A

Protein A – binds Fc region of IgG

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10
Q

What gene confers methicillin resistance in S. aureus (MRSA)?

A

mecA gene – encodes altered penicillin-binding protein (PBP2a).

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11
Q

Which disk test screens for MRSA in the lab?

A

Cefoxitin disk diffusion:
Zone ≤ 21 mm = MRSA
Zone ≥ 22 mm = MSSA

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12
Q

Is S. aureus catalase and coagulase positive or negative?

A

Catalase-positive, coagulase-positive.

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13
Q

Name two toxin-mediated diseases caused by S. aureus.

A

Toxic Shock Syndrome (TSS toxin-1)
Food poisoning (enterotoxins)

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14
Q

What is the treatment of choice for MRSA infections?

A

Vancomycin

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15
Q

What Staphylococcus species is commonly associated with prosthetic device infections?

A

S. epidermis

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16
Q

List the virulence factors associated with Staphylococcus auerues?

A

Enterotoxins
Cytolytic Toxins
Enzymes
Protein A

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17
Q

Which toxins produced by S. aureus are responsible for food poisoning?

A

Enterotoxins (especially Enterotoxin A) – heat-stable superantigens

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18
Q

Which toxin causes toxic shock syndrome by acting as a superantigen?

A

Toxic Shock Syndrome Toxin-1 (TSST-1)

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19
Q

What causes Toxin Shock Syndrome Toxin-1

A

When staphylococcus aureus enters the bloodstream and stimulates T cell proliferation and the subsequent productions of a large amount of cytokines that are responsible for the symptoms.

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20
Q

What toxin is responsible for the blistering skin seen in scalded skin syndrome?

A

Exfoliative toxin (ETA, ETB) – cleaves desmoglein-1 in skin. Causes the epidermal a;yer of the skin to slough off. Mostly seen in newborns and children.

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21
Q

Describe cytolytic toxins?

A

S. aueres produces extracellular proteins that affect red blood cells and leukocytes. THe are hemolysins and leukocidins.

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22
Q

Describe the 4 hemolysins:

A

Alpha: lyses erythrocytes and can damage platelets and macrophages and causes severe tissue damage.
Beta: acts on sphingomyelin in the plasma membrane of erythrocytes. CAMP test are performed to identify Beta strept.
Delta: less toxic than alpha and beta hemolysin
Gamma: only associated with Panton-Valentine Leukocidin (PVL). PVL is lethal to polymorphonuclear leukocytes.

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23
Q

What are the function of the different enzymes produced by S. aueres?

A

Staphylocoagulase converts fibrinogen to fibrin and is considered a virulent marker
Protease, lipase and hyaluronidase are capable of destroying tissue and may facilitate the spread of infection to adjoining tissue.

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24
Q

What is the function of Protein A?

A

Protein A has the ability to bind to the Fc portion of IgG and block phagacytosis and negate the protective effects of IgG.

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25
Where would you find S. epidermis?
Normal Skin microbiota
26
What are kind of infections are caused by S. epidermis?
Hospital Acquired infection such as catherization, medical implanation and immunosuppressive therapy. Also causes septicemia in immunocompromised patients and health care acquired UTIs
27
What is the key component of S. epidermis that prevents phagocytosis?
Biofilm production
28
Is S. saprophyticus catalase positive or negative?
Catalase-positive
29
Is S. saprophyticus coagulase positive or negative?
Coagulase-negative
30
What kind of hemolysis does S. saprophyticus produce on blood agar?
Usually non-hemolytic (gamma hemolysis
31
Is S. saprophyticus considered part of normal flora? If so, where?
Yes – in the genitourinary tract and perineal area
32
Does S. saprophyticus grow on Mannitol Salt Agar (MSA)?
Yes – it grows (salt-tolerant), but usually does not ferment mannitol (agar remains pink)
33
Why is novobiocin resistance clinically useful?
It helps distinguish S. saprophyticus from other CoNS like S. epidermidis in UTI workups.
34
What population is S. saprophyticus most commonly isolated from?
Sexually active young women
35
What infections are associated with Staphylococcus Lugdunensis?
Community associated and hospital acquired infections -> endocarditis, septicemia, meningitis, skin and soft tissues infections, UTIs and septic shock.
36
What does MRSA stand for?
Methicillin-Resistant Staphylococcus aureus
37
What gene is responsible for methicillin resistance in Staphylococcus?
mecA gene – encodes PBP2a, an altered penicillin-binding protein
38
Why are staphylococcus aueres resistant to penicillin?
S. aueres produce B lactamase which breaks down the cell wall of penicillin and now makes penicillin ineffective.
39
How do you differentiate between streptococcus and staphylococcus if they are both gram positive cocci?
Streptococcus and enterococcus is catalase negative and staphylococus is catalase positive
40
What is the catalase test?
Test used to detect the catalase enzyme. Bacteria that contain the catalase enzyme can break down hydrogen peroxide to oxygen and water.
41
What is the Bile Esculin Test?
It is used to determine which organism that hydroylzed esculin and grow in the presence of bile salts. If the medium turns black in 24 to 48 hours it is positive.
42
What is the purpose of the Bile Esculin Test?
Used to identify and differentiate Group D enterococcus (bile esculin positive) from non hemolytic streptococcus (bile esculin negative)
43
What is the Lancefield Grouping?
Classifies Beta Hemolytic Streptococcus based on specific carbohydrate antigens
44
What are the different Lancefield Groups?
Group A: S. pyogenes Group B: S. agalactiae Group D: S. bovis and Enterococcus
45
What streptococcus is beta hemolytic and PYR and Bactiracin susceptible?
Streptococcus Pyogenes
46
What are the virulence factors of Streptococcus Pyogenes?
M protein Streptolysin O Lipoteichoic Acid Protein F Hyaluronidase Streptolysin S
47
How does protein M cause virulence for S. pyogenes?
M protein resist phagocytosis and plays a role in adherence of the bacterial cell to the mucosal membrane
48
What is the function of streptolysin O?
Lyse Leukocytes, RBCS and platelets
49
How does hyaluronidase contribute to the virulence of S. pyogenes?
It help spreads the infection/inflammation
50
How does protein F contribute to the virulence of S. pyogenes?
Protein F adheres the bacterial cell to the epithelial cell.
51
What two diseases are associated with S. pyogenes?
Rheumatic Fever and Acute Glomerulonephritis
52
Which gram positive cocci is catalase negative, beta hemolytic, PYR and bacitracin negative and CAMP positive?
Streptococcus Agalactiae
53
What are the virulence factors for Streptococcus Agalactiae?
Capsule: prevents phagocytosis Hemolysin, neurominidase, DNase, Hyaluronidase, protease CAMP factor
54
Describe the CAMP factor test?
CAMP is a protein that enhances the lysing of RBC when it interacts with staphylococcus aueres. Blood is streak down the center of the plate. Suspected streptococcus is streaked perpendicular (not touching the S. aueres). A positive CAMP will have a distinct arrowhead shape hemolysis as it approached the S. aueres.
55
What are clinical significance of S. agalactiae?
Can cause deaths in neonates through obstetic complications, prolong rupture of membranes and premature birth. All pregnant women should be screen. It can also caused skin and soft tissue infections, intrabdominal abscess, bacterimia, pneumonia, endocarditis or UTIs.
56
What gram positive cocci is catalase negative, alpha hemolytic and optochin sensitive?
Streptococcus Pneumoniae
57
What are the virulence factor of S. pneumoniae?
Capsular polysaccharide Reacts with CRP to increase infections and inflammations Neurominidase, hyaluronidase, protease A and hemolysin
58
What are the clinical significance of S. pneumoniae?
Bacterial pneumonia, meningitis, otitis media, bacteremia
59
Which gram positive cocci is alpha hemolytic, optpchin resistant and bile esculin negative?
Viridans Streptococcus
60
Describe Viridens Streptococcus
Normal microbiota in the upper respiratory, female genital tract and and gastrointestinal tract.
61
What are the virulence factors of viridans strep.
Polysaccharide capsule Cytolysin Extracellular dextran and cell surface proteins
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