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phase 2a > gram positive bacteria > Flashcards

gram positive bacteria Flashcards

1
Q

how do gram positive bacteria stain and what colour?

A

Gram positive bacteria retain the colour of the crystal violet stain in the gram stain (because they have a cell wall composed of a thick layer of peptidoglycan).
They stain purple.

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2
Q

how are streptococci classified?

A

1.Haemolysis
2.Lancefield typing
3. Biochemical properties

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3
Q

what is lancefield grouping?

A

a method of grouping catalyse negative, coagulase negative bacteria based on bacterial carbohydrate cell surface antigens

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4
Q

name some important gram positive bacteria

A

S.aureus, S.epidermis, S.pyogenes, S.pneumoniae, viridans streptococci, C.diphtheriae

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5
Q

how are gram positive bacteria spread?

A

Spread by aerosols, surface-to-surface contact, colonization of prostheses

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6
Q

how are gram positive bacteria managed?

A

Managed with antimicrobials and vaccination

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7
Q

clinical case 1-
Pain in shoulder, elevated temperature
MRI scan, disc infection and osteomyelitis C6 &C7,
Blood cultures

A

Staphylococcus aureus; flucloxacillin 3 months

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8
Q

what is coagulase?

A

enzyme produced by bacteria that clots blood plasma. Fibrin clot formation around bacteria may protect from phagocytosis.

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9
Q

what is the most important +ve coagulase?

A

s. aureus

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10
Q

when are coagulase -ve species important?

A

in opportunistic infections

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11
Q

what is the normal habitat of staphylococci?

A

nose and skin

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12
Q

how is staphylococcus aureus spread?

A

Spread by aerosol and touch
carriers & shedders

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13
Q

what are the virulence factors of staphylococcus?

A

Pore-forming toxins (some strains)
a - haemolysin & Panton-Valentine Leucocidin
Proteases
Exfoliatin
Toxic Shock Syndrome toxin (stimulates cytokine release)
Protein A (surface protein which binds Ig’s in wrong orientation)

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14
Q

what is MRSA resistant to?

A

beta-lactams
gentamicin, erythromycin,
tetracycline

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15
Q

S. AUREUS -name some toxic mediated diseases

A

Scalded skin syndrome
Toxic shock syndrome
Food poisoning

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16
Q

S. AUREUS -name some pyogenic diseases

A

Wound infections
Abscesses (boils, carbuncles)
Impetigo
Septicaemia
Osteomyelitis
Pneumonia
Endocarditis

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17
Q

What is the main virulence factor for S.epidermidis ?

A

ability to form persistent biofilms

18
Q

where does S.epidermidis normally occur?

A

Infections in debilitated, prostheses (opportunistic)

19
Q

alpha haemolysis

A

not complete lysis/clearing
still green tinge to it

20
Q

beta haemolysis

A

complete lysis/clearing

21
Q

what is sero grouping?

A

grouping based on Carbohydrate cell surface antigens
one method is lance field A-H and K-V

22
Q

describe lance field A-H and K-V

A

Antiserum to each group added to a suspension of bacteria
clumping indicates recognition

23
Q

what are the two groups of lancefield sero grouping?

A

group A- S.pyogenes; important pathogen
Group B - S.agalactiae neonatal infections

24
Q

S.pyogenes virulence factors- exported factors

A

Hyaluronidase - spreading
Streptokinase - breaks down clots
C5a peptidase - reduces chemotaxis

25
Q

S.pyogenes virulence factors- surface factors

A

Capsule - hyaluronic acid

M protein – surface protein
(encourages complement degradation)

26
Q

S.pyogenes virulence factors- toxins

A

Streptolysins O&S - binds cholesterol
Erythrogenic toxin - SPeA – exaggerated response

27
Q

name some infections caused by S. pyogenes

A

Wound infections&raquo_space; cellulitis, puerperal fever
Tonsillitis & pharyngitis
Otitis media
Impetigo
Scarlet fever
Complications
rheumatic fever
glomerulonephritis

28
Q

what is s.pneumoniae?

A

Normal commensal in oro-pharynx ~ 30% of population

29
Q

causes of s.pneumoniae?

A

pneumonia, otitis media, sinusitis, meningitis

30
Q

what are the predisposing factors of s.pneumoniae?

A

impaired mucus trapping (e.g. viral infection)
hypogammaglobulinaemia
asplenia

31
Q

what are the virulence factors of S.pneumoniae?

A

Capsule
Inflammatory wall constituents
teichoic acid (choline)
peptidoglycan
Cytotoxin

32
Q

what are the virulence factors of S.pneumoniae?- capsule

A

polysaccharide (84 types), antiphagocytic
polyvalent vaccine
23-valent polysaccharide
13-valent conjugate vaccine

33
Q

what are the virulence factors of S.pneumoniae?- inflammatory wall constituents

A

teichoic acid (choline)
peptidoglycan

34
Q

what are the virulence factors of S.pneumoniae?- cytotoxin

A

pneumolysin

35
Q

what are viridian’s group streptococci?

A

- haemolytic (or non-haemolytic)
Some cause dental caries & abscesses

36
Q

when Is viridian’s group streptococci important?

A

Important in infective endocarditits
S. sanguinis, S. oralis

37
Q

what causes viridian’s group streptococci?

A

Cause deep organ abscesses (e.g. brain, liver)

38
Q

what are the most virulent-viridian’s group streptococci?

A

the “milleri group”
S.intermedius, S.anginosus, S.constellatus

39
Q

gram positive bacilli

A

Clostridia

C. tetani
Tetanus

C. botulinum
Botulism

C. difficile
antibiotic associated diarrhea
pseudomembranous colitis

Listeria monocytogenes

Bacillus anthracis

Corynebacterium diphtheriae

40
Q
A

phase 2a (67 decks)

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