Staph & Strep Flashcards

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1
Q

Describe Staphylococcal Infection

A
  • infection occurs when staphylococci breaches the body’s physical barriers
  • transmission is via direct contact from person to person but also from contaminated clothing, sheets & medical instruments
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2
Q

What different factors affect infection ?

A
  • site infection
  • immune status of host
  • different virulence factors
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3
Q

What are the 3 categories of disease ?

A
  1. Noninvasive
  2. Cutaneous
  3. Systemic
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4
Q

What are 3 virulence factors ?

A
  • evasion from phagocytosis
  • production of enzymes
  • production of toxins
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5
Q

Describe Group A streptococci

A
  • infects the pharynx & skin
  • abscesses are short lived
  • large inoculum is required & usually disease results when competing microbiota are depleted or immune status is poor
  • can be spread from person to person
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6
Q

Describe Streptococcus pneumoniae

A
  • common pathogens = 92 strains known infect humans
  • lacks Lancefield antigens
  • alpha-haemolytic on blood agar in aerobic conditions
  • beta-haemolytic = anaerobic conditions
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7
Q

Describe Staphylococci Gram Stain

A
  • gram positive cocci
  • singly & grape-like clusters
  • facultatively anaerobic
  • non-motile
  • salt tolerant
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8
Q

Describe Streptococci Gram Stain

A
  • gram postive cocci
  • pair & chains
  • facultatively anaerobic
  • non-motile
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9
Q

How can you distinguish between staph & strep using a catalase test ?

A
  • Staphylococci = catalase positive
  • streptococci = catalase negative
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10
Q

Describe the Coagulase test

A
  • members of the genus Staphylococcus are differentiated by the ability to clot plasma by enzyme coagulase
  • enables the conversion of fibrinogen to fibrin
  • binds plasma fibrinogen, causing the organism to agglutinate/clot
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11
Q

What is the difference between S. aureus & S.epidermidis on blood agar?

A

-S. aureus appears as translucent colonies that often have a gold pigment
- S. epidermidis appear as greyish-white colonies

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