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Clinical Microbiology > Gram positive bacteria > Flashcards

Gram positive bacteria Flashcards

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Biology 101 flashcards
1
Q

What arrangements are:
1. Streptococcus
2. Staphylococcus
usually in?

A
  1. Pairs and chains

2. Clusters

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2
Q

General properties of staphylococci

A

Facultative anaerobes
Catalase +
Found on the skin and mucous membranes
More than 20 species, but 4 are commonly associated with disease

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3
Q

4 species of Staph that are commonly associated with human disease

A
  1. S. aureus
  2. S. ludgunensis
  3. S. epidermidis
  4. S. saprophyticus
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4
Q

Catalase test

A

Determines if the organism produces catalase
This enzyme breaks down H2O2 into water and oxygen
Catalase allows organisms to break down harmful metabolites of aerobic respiration and may be seen in aerobic and facultative anaerobic organisms

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5
Q

Catalase test results for:

  1. Staph
  2. Strep
  3. Enterococcus
A
  1. Positive
  2. Negative
  3. Negative
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6
Q

S. aureus

A

10-15% of people carry it in their nose or other mucus membranes - frequency increases in hospitals
Most frequent cause of hospital acquired infections
MRSA is an increasing concern
Slide and tube coagulase +
Golden colour

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7
Q

Slide coagulase

and which organisms are positive

A

Looking for clumping factor
Latex agglutination test
Positive: S. aureus and S. lugdenensis

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8
Q

Tube coagulase

and which organisms are positive

A

Looking for free coagulase
Performed in rabbit plasma
Positive: s. aureus and s. pseudintermedius
Only considered coagulase positive if you are tube +

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9
Q

Coagulase negative staphylococci

A

Every carries CNS on their skin
Virtually impossible to eradicate it, even with disinfectant use and hand washing
Produce slime and have a high affinity for synthetic materials - devices inserted through skin are frequently infected

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10
Q

S. lugdunensis

A 
Coagulase negative Staplococcus spp
Considered as virulent as S. aureus
Similar clinical spectrum
Produces clumping factor (slide coagulase +)
PYR +
Ornithine decarboxylase +
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11
Q

S. saprophyticus

A

UTI pathogen associated with young women

Resistant to novobiocin

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12
Q

S. pseudintermedius

A

Slide coag -‘ve, tube coag +’ve
Animal pathogen that is increasingly being reported in human disease
Methicillin resistant
Used to be misidentified as staph aureus

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13
Q

4 shared characteristics of enterococci

A
  1. Growth at 6.5% NaCl at pH 9.6
  2. Growth between 10-45 degC
  3. Growth in 40% bile
  4. Esculin hydrolysis, LAP, and PYR +
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14
Q

4 clinical isolates of enterococci and what are they all resistant to

A

Common:
E. faecalis (80-90%, and is susceptible to ampicillin)
E. faecium (5-10%, and is resistant to ampicillin)
Less common:
E. casseliflavus
E. gallinarum
All are intrinsically resistant to cephalosporins
Vancomycin resistant enterococci is a concern

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15
Q

3 General characteristics of streptococcaceae

A
  1. Gram positive chains/pairs
  2. Catalase negative
  3. Facultative anaerobes
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16
Q

3 strep species in Viridans group

A

S. mutans
S. sanuis
S. salavarius

17
Q

3 types of haemolysis

A

Beta: complete
Alpha: partial (greening of agar)
Gamma: none

18
Q

S. pyogenes

remember: sensitive to..

A

Group A strep
Highly beta hemolytic
Mid sized colonies with big zone of hemolysis
Use Taxo A disk - has Bacitracin - they are SENSITIVE
PYR +
Never resistant to penicillin or any beta lactam

19
Q

Beta hemolytic strep are never resistant to…

A

Penicillin or any beta lactam

20
Q

PYR test

which organisms are positive, and which are negative

A

Enterococcus and Grp A = +

S. bovis and other Streptococci = -

21
Q

S. agalactiae

A 
Grp B Strep
Weakly beta hemolytic
Colonies tend to be smaller than group A
CAMP test +
All women should be screened late in pregnancy, because it can cause major problems in newborns
22
Q

CAMP test

A

Differentiates Gp B from other strep
Synergistic hemolysis observed between S. aureus and Gp B strep
Positive reaction = arrow head hemolysis
Listeria also positive

23
Q

Streptococcus anginosus group

A 
3 species
Weakly beta, sometimes alpha
Primarily group F or A - also C and G
Colonies smell like caramel/butterscotch
Associated with deep seated abscesses (liver/brain)
24
Q

3 species in Streptococcus anginosus group

A

S. anginosus
S. intermedius
S. constellatus

25
Q

Streptococcus bovis group

A

Divided into 4 related species
Gp D antigen
Capable of growth in presence of bile, hydrolyzes esculin
May be linked to occult colon cancer if grown from blood
Important to differentiate from Enterococcus spp

26
Q

4 species in Streptococcus bovis group

A

S. equinus
S. gallolyticus
S. infantarius
S. alactolyticus

27
Q

3 similarities between S bovis and Enterococci

And 2 ways to distinguish

A

Both Gp D, bile esculin positive, and usually non-hemolytic

Enterococci is PYR + and capable of growth in 6.5% NaCl

28
Q

S. pneumoniae

A

Bile soluble and optochin sensitive

Alpha hemolytic strep

29
Q

Nutritionally variant streptococci

A

Key: require vitamin B6 for growth
Biochemically similar to viridians group (optochin R, bile insoluble, alpha hemolysis)
PYR positive

30
Q

Listeria monocytogenes

gram stain, catalase/CAMP test, resistant to, motility, hemolysis

A 
Gram positive
Catalase positive
Tumbling motility at 25 degC
Umbrella motility in semi-soft agar
Beta hemolytic
CAMP test +
Intrinsically resistant to cephalosporins
31
Q

Corynebacterium spp

A 
Gram positive bacilli
Commonly found on skin
Catalase +
Contaminant
3 pathogenic species
32
Q

3 pathogenic species of Corynebacterium

A

C. diphtheriae
C. pseudodiptheriticum
C. urealyticum

33
Q

MRSA is resistant to…

A

Penicillins and cephalosporins

any beta lactam

34
Q

What test is used to identify Staph aureus?

A

Coagulase

its is slide and tube +

35
Q

What test is positive for all staph organisms?

A

Catalase

Clinical Microbiology (25 decks)

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