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Streptococci Flashcards

1
Q

are streps gram positive or negative?

A

positive

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2
Q

are streps catalase positive or negative?

A

negative

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3
Q

what kind of anaerobes/aerobes are streps?

A

facultative anaerobes

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4
Q

how are streps classified?

A

haemolysis

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5
Q

what is alpha haemolysis?

A

partially broken down blood

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6
Q

what colour is alpha haemolysis?

A

green tinge

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7
Q

what is beta haemolysis?

A

completely breaks down the blood

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8
Q

what is gamma haemolysis?

A

not really haemolytic - enterococci

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9
Q

what is viridans group?

A

alpha haemolysis

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10
Q

where do viridans streptococci live?

A

mouth, pharynx, genital tract

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11
Q

what are viridans strep susceptible to?

A

penicillin

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12
Q

if a patient is immunocompromised, what can viridans strep cause? (opportunistic pathogens)

A

endocarditis, meningitis

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13
Q

what kinds of strep cause dental decay?

A

strep mutans

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14
Q

how does strep pneumoniae haemolyse when grown anaerobically?

A

beta haemolysis

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15
Q

how does strep pneumoniae haemolyse normally?

A

alpha haemolysis

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16
Q

what does strep pneumoniae cause?

A

pneumonia, sinusitis, endocarditis, meningitis

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17
Q

what is different about virulent strep pneumoniae strains?

A

capsulated

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18
Q

how many strains of strep pneumoniae are there?

A

92

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19
Q

how are the different strains of strep pneumoniae serotyped?

A

capsular antigens

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20
Q

who does strep pneumoniae usually infect?

A

children and the elderly

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21
Q

case study:

  • Elderly patient
  • cough and chest pain
  • purulent sputum
  • shaking chill and developed fever
  • high temp and severe chest pain

what is the diagnosis?

A

pneumonia

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22
Q

how would you examine pneumonia?

A

chest radiograph: infiltrate
high wbc count
Gram stain of sputum
blood & sputum sent to lab for culture

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23
Q

what could you do to diagnose pneumonia?

A

Gram stain – easy to spot in sputum smears
Quellung reaction -anti capsular antibodies cause capsule to swell
Typical dimpled colonies
Bile solubility
Optochin sensitivity test

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24
Q

what is quellung reaction?

A

Anticapsular antibodies cause capsule to swell

Stain with Indian ink, capsule easily visible

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25
is strep pneumoniae optochin sensitive or resistant?
sensitive
26
how are beta haemolytics classified?
lancefield groups - based on antigens
27
how is lancefield grouped?
agglutination tests
28
what are the lancefield groups?
A, B, C, D, F, G
29
which lancefield groups are most medically important and which are rare?
most medically important - A, B, D | most rare - C, G, F
30
why cant you identify strep pneumoniae or strep viridans by lancefield grouping?
only beta haemolytics
31
what is a key feature of lancefield group A?
sore throat, scarlet fever, impetigo
32
what is a key feature of lancefield group B?
neonatal sepsis & meningitis
33
what are key features of lancefield groups C and G?
abscesses
34
what is a key feature of lancefield group D?
endocarditis & dental caries
35
which lancefield group does strep pyogenes belong to?
group A
36
enterococcus used to be classified as which lancefield group?
group D
37
where is strep pyogenes found?
Skin, mucous membranes
38
how is strep pyogenes spread?
person-person, droplets & direct contact
39
what 4 things does non-invasive strep pyogenes cause?
Pharyngitis (strep throat) Impetigo Scarlet fever cellulitis
40
what 4 things does invasive strep pyogenes cause?
Toxic shock-type syndrome Necrotizing fasciitis Rheumatic fever Glomerulonephritis
41
what virulence factors does strep pyogenes have and what do they do?
fimbrae: protein F M protein hyaluronic acid lipoteichoic acid
42
what does fimbrae: protein F do?
attachment and adherence
43
what does M protein do?
resistance to phagocytosis
44
what does hyaluronic acid do?
prevents phagocytosis
45
what does lipoteichoic acid do?
adheres to molecules on host epithelial cells
46
how does strep pyogenes multiply?
M protein binds to fibrinogen and stops it from working. this blocks complement and binds to factor H
47
how does strep pyogenes spread infection?
skin- localised pharynx- ear, sinuses wound- rapid spread virulence factors - proteases, DNAse, streptokinase, hyaluronidase
48
what is the action of streptokinase?
Induces fibrinolysis which egrades fibrin and other proteins which affects clotting -> clotting localises infection so it spreads
49
what does hyaluronic acid do?
breaks down the hyaluronic acid in connective tissue bacteria turns off hyaluronidase production at epithelial surfaces instead of capsule formation
50
what pyrogenic toxins cause damage?
ABC
51
what are pyrogenic toxins?
erythrogenic toxins that suppress antibody responses and stimulate cytokines - septic shock
52
what are the symptoms of a strep pyogenes throat infection?
``` Hot flushed sore throat vomiting high temperature red throat greyish white exudate enlarged lymph nodes ```
53
what can be complications of strep pyogenes?
scarlett fever and rheumatic fever
54
what is acute rheumatic fever?
life threatening fever, affects the joints and heart
55
how does acute rheumatic fever affect the heart?
autoimmune response - antistrep antibodies cross react with heart cell antigens, causing scarring
56
how do you prevent acute rheumatic fever?
penicillin treatment of pharyngitis
57
what is necrotising fascitis?
'flesh eating bacteria' | faster than antibiotics work
58
what are the treatment options for necrotising fascitis?
amputation
59
how do you diagnose strep pyogenes?
culture of pus and blood | lancefield agglutination tests
60
is strep pyogenes bacitracin sensitive or resistant?
sensitive
61
group B lancefield - example
Strep. agalactiae
62
where are group B lancefields found?
Lower GI & female genital tracts
63
what can group B cause?
``` neonatal sepsis neonatal meningitis cellulitis arthritis meningitis ```
64
who does group B affect?
diabetics elderly alcoholics immunocompromised
65
are group B bacitracin sensitive or resistant?
resistant
66
how do you treat group B infections?
penicillin at high concentrations
67
how do group F grow?
microaerophilic/anaerobic
68
where is group F found?
Normal flora oropharynx
69
what is the appearance of group F on media?
tiny colonies
70
what can group F cause?
abscesses in soft tissue
71
what is an example of a group F?
Strep milleri
72
where is enterococci found?
the gut
73
is enterococci bile resistant or sensitive?
resistant

X Infectious Diseases (9 decks)

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