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Medical Microbiology and Parasitology > Gram positive cocci > Flashcards

Gram positive cocci Flashcards

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Biology 101 flashcards USMLE® Step 1 flashcards
1
Q

Gram positive bacterial cell wall

A

Has a thick peptidoglycan layer that contains teichoic and lipoteichoic acids

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2
Q

Gram negative bacterial cell wall

A

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

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3
Q

What is the colour of positive gram staining bacteria?

A

Purple

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4
Q

What is the colour of negative gram staining bacteria?

A

Pink or Red

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5
Q

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

A

Staphylococci

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6
Q

What are the three staphylococcal species?

A

Staphylococcus aureus, epidermis, and saprophticus

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7
Q

What is the confirmatory test for Staphylococcus aureus?

A

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.

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8
Q

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

A

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

The agar remains pink for Staphylococcus epidermis

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9
Q

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

A

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

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10
Q

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

A

Beta-haemolytic, complete lysis of blood

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11
Q

Catalase test

A

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

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12
Q

How is S.aureus transmitted?

A

Direct contact or exposure to contaminated fomites

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13
Q

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

A

S.aureus virulence factor

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14
Q
  • enterotoxin (contaminated food)
  • symptoms: vomiting, nausea, diarrhea, abdominal cramps
A

Staphylococcal food poisoning

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15
Q
  • exfoliative toxin
  • symptoms: peeling off skin, exfoliative dermatitis, fever (infections)
  • most commonly in children
A

Staphylococcal scalded skin syndrome (ritter’s disease)

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16
Q

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

A

Inflammatory diseases of S.aureus

17
Q
  • TSST-1
  • symptoms: fever, myalgia, hypotension, vomiting, diarrhea, and rashes
A

Staphylococcal Toxic Syndrome

18
Q

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

A

Treatment for Staphylococci

19
Q

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

A

Streptococcus pyogenes

20
Q

Conformational test for S.pyogenes

A

Streptococcal grouping (Lancefield classification)

21
Q

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

A

Streptococcus

22
Q

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

A

Virulence factor of S.pyogenes

23
Q

Respiratory infections
- pharyngitis (strep throat)

A

S.pyogenes

24
Q

skin infections
- cellulitis
- pyoderma
-necrotizing fasciitis

A

S.pyogenes

25
Q

Scarlet fever
Streptococcal toxic shock syndrome

A

S.pyogenes

26
Q

acute glomerulonephritis
rheumatic fever

A

S.pyogenes

27
Q

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

A

Treatment for S.pyogenes and S.pneumoniae

28
Q

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

A

S.pneumoniae

29
Q

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

A

S.pneumoniae

30
Q

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

A

Enterococci

31
Q

Bacteremia
UTI
Endocarditis
Wound infections

A

Enterococci

Medical Microbiology and Parasitology (14 decks)

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