Gram positive cocci

Question 1

Gram positive bacterial cell wall

Answer 1

Has a thick peptidoglycan layer that contains teichoic and lipoteichoic acids

Question 2

Gram negative bacterial cell wall

Answer 2

Has a think peptidoglycan layer and an outer membrane that contains lipopolysaccharide (LPS), phospholipids, and protein

Question 3

What is the colour of positive gram staining bacteria?

Answer 3

Purple

Question 4

What is the colour of negative gram staining bacteria?

Answer 4

Pink or Red

Question 5

Gram positive cocci arranged in singles, pairs, tetrads or grape-like clusters.
Non-motile, non-spore forming but occasionally capsulated
Aerobic and facultative anaerobic, catalase positive, and oxidase negative

Answer 5

Staphylococci

Question 6

What are the three staphylococcal species?

Answer 6

Staphylococcus aureus, epidermis, and saprophticus

Question 7

What is the confirmatory test for Staphylococcus aureus?

Answer 7

Coagulase test. Only staphylococcus aureus is coagulase positive which differentiates it from other species.

It produces an enzyme called coagulate that converts fibrinogen to fibrin, promoting clotting of blood or plasma.

Question 8

How to differentiate Staphylococcus aureus and epidermis on Mannitol Salt Agar (MSA)?

Answer 8

Staphylococcus aureus turns the agar yellow as it ferments mannitol with acid.

The agar remains pink for Staphylococcus epidermis

Question 9

What is the observation of S.aureus colonies on BPA?

Answer 9

Black colonies due to the reduction of tellurite in egg yolk
The clear zones surrounding the black colonies indicates the production of lecithinase, the breaking down of egg yolk

Question 10

What is the observation of S.aureus colonies on blood agar?

Answer 10

Beta-haemolytic, complete lysis of blood

Question 11

Catalase test

Answer 11

2H2O2 —> 2H2O + O2
The formation of bubbles indicates a positive rsesult

Question 12

How is S.aureus transmitted?

Answer 12

Direct contact or exposure to contaminated fomites

Question 13

Structural: Protein A (helps to invade immune system by binding to IgGA), capsule, teichoic acid, peptidoglycan, and slime layer

Toxins: cytotoxin, exfoliative toxin (ritter’s syndrome), enterotoxins (food poisoning), and TSST-1 (toxic shock syndrome)

Enzymes: coagulase and hyaluronidase

Answer 13

S.aureus virulence factor

Question 14

• enterotoxin (contaminated food)
• symptoms: vomiting, nausea, diarrhea, abdominal cramps

Answer 14

Staphylococcal food poisoning

Question 15

• exfoliative toxin
• symptoms: peeling off skin, exfoliative dermatitis, fever (infections)
• most commonly in children

Answer 15

Staphylococcal scalded skin syndrome (ritter’s disease)

Question 16

1) Skin: Folliculitis and impetigo
2) Blood: bacteremia, septicemia, and endocarditis (travel to heart)
3) Bone: osteomyelitis and septic arthritis
4) Brain: meningitis and brain abscess

Answer 16

Inflammatory diseases of S.aureus

Question 17

• TSST-1
• symptoms: fever, myalgia, hypotension, vomiting, diarrhea, and rashes

Answer 17

Staphylococcal Toxic Syndrome

Question 18

Penicillin cannot be used
Derivatives of penicillin: nafcillin, oxacillin, and methicillin
MRSA: cephalosporins
MRSE: vancomycin + rifampicin
VRSA: vancomycin intermediate

Answer 18

Treatment for Staphylococci

Question 19

Gram positive cocci, chains, catalase negative, oxidase negative, Beta-haemolytic, Group A

Answer 19

Streptococcus pyogenes

Question 20

Conformational test for S.pyogenes

Answer 20

Streptococcal grouping (Lancefield classification)

Question 21

Aerobic and facultatively anaerobic, Gram positive cocci, arranged in pairs or chains. Non-motile, non-sporing, catalase negative.
Classified by:
Group specific carbohydrates
Haemolytic properties

Answer 21

Streptococcus

Question 22

Structural: capsulated, teichoic acid, M and F protein
Toxins: Streptococcal pyrogenic exotoxins (SPEs), Streptolysin O and S, Pyrogenic exotoxins
Enzymes: ribonucleases, hyaluronidase, and streptokinase

Answer 22

Virulence factor of S.pyogenes

Question 23

Respiratory infections
- pharyngitis (strep throat)

Answer 23

S.pyogenes

Question 24

skin infections
- cellulitis
- pyoderma
-necrotizing fasciitis

Answer 24

S.pyogenes

Question 25

Scarlet fever
Streptococcal toxic shock syndrome

Answer 25

S.pyogenes

Question 26

acute glomerulonephritis
rheumatic fever

Answer 26

S.pyogenes

Question 27

Penicillin is a drug of choice
Erythromycin for those who are allergic to penicillin

Answer 27

Treatment for S.pyogenes and S.pneumoniae

Question 28

Gram positive cocci, pairs, alpha-haemolytic, encapsulated, catalase negative, no grouping

Answer 28

S.pneumoniae

Question 29

Pneumonia (bacteria multiply in alveolar spaces)
Sinusitis
Otitis (ear canal inflammation)
Meningitis
Bacteremia
Sepsis

Answer 29

S.pneumoniae

Question 30

Gram positive, oval, pairs, Group D, resistance to all antibiotics, patient to patient spread

Answer 30

Enterococci

Question 31

Bacteremia
UTI
Endocarditis
Wound infections

Answer 31

Enterococci