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Clinical Micro > Gram positive bacteria identification > Flashcards

Gram positive bacteria identification Flashcards

1
Q

What is the main division between the gram positive cocci?

A

The ones that grow in chains/pairs and the ones that grow in clusters.

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2
Q

Which genus/genera of bacteria grow in clusters?

A

Staphylococcus

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3
Q

Which genus/genera of bacteria grow in chains/pairs?

A

Enterococcus and Streptococcus

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4
Q

What is the catalase test?

A

determines if the organism produces the enzyme “catalase”, which breaks down hydrogen peroxide (H2O2) to water and oxygen (O2).

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5
Q

What is the usefulness of catalase?

A

allows organisms to break down harmful metabolites of aerobic respiration and may be seen in aerobic and facultative anaerobic organisms

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6
Q

What are the two forms of the coagulase test? what makes them different?

A
  1. Slide coagulase: you’re not actually looking for coagulase, you’re looking for clumping factor
  2. Tube coagulase: put rabbit plasma and test organism in a tube, if it is positive it will solidify the sample
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7
Q

What makes an organism considered “coagulase negative”

A

Either negative for both tests or slide positive and tube negative

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8
Q

How common are coagulase negative staph?

A

Very. Everyone has them on their skin

- almost impossible to get rid of

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9
Q

What are the 4 species of staph that are commonly associated with human disease?

A

S. aureus, S.lugdunensis, S. epidermidis, and S. saprophyticus

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10
Q

Out of the gram positive cocci, which are positive for the catalase test and which are negative?

A

Positive for Staphylococcus, Negative for Enterococcus and Streptococcus

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11
Q

What is a key diagnostic (test) feature to identify S. aureus ?

A

It is both tube and slide coagulase positive

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12
Q

What are 2 common features of all Staphylococci? where are they commonly found?

A

Facultative anaerobes.
Catalase +
Commonly found on human skin and mucous membranes.

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13
Q

What gram positive cocci is the most frequent cause of hospital acquired infections?

A

S. aureus

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14
Q

What percentage of people carry S. aureus in their nose or other mucous membranes?

A

10-15% of people

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15
Q

What are two important coagulase negative Staph species?

A

S. lugdunensis and S. saprophyticus

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16
Q

What is the testing profile of S. lugdunensis?

A

Slide coagulase +
Tube coagulase - (considered coag. neg)
PYR +
Ornithine decarboxylase +

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17
Q

S. lugdunensis is considered just as virulent as?

A

S. aureus, has a similar clinical spectrum

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18
Q

What is S. saprophyticus commonly associated with?

A

UTIs in young women

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19
Q

What is the coagulase profile of S. pseudintermedius?

A

Slide coagulase -

Tube coagulase +

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20
Q

What is S. pseudintermedius a pathogen of typically?

A

Dogs

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21
Q

What is S. pseudintermedius frequently resistant to?

A

Methicillin

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22
Q

S. pseudintermedius was frequently identified incorrectly as __ before MALDI-TOF?

A

MRSA

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23
Q

Are the majority of Enterococci pathogenic to humans?

A

No

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24
Q

What are the common growth characteristics of the enterococci? (3 features)

A

Growth at 6.5% NaCl at pH 9.6
Growth between 10-45oC
Growth in 40% bile

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25
Q

What is the testing profile of the Enterococci?

A

PYR +
Esculin hydrolysis +
LAD (?)

26
Q

What are the Enterococci intrinsically resistant to? What antibiotic is there growing resistance to?

A

Intrinsically resistant to cephalosporins. Increased resistance to Vancomycin

27
Q

What are two common clinical Enterococcal isolates ? what percentages?

A

E. faecalis (80-90%)
E. faecium (5-10%)
- faecium is harder to treat

28
Q

What are 3 general characteristics of the Streptococci?

A

Gram positive cocci in chains/pairs
Facultative anaerobes
Catalase negative

29
Q

What are the 3 groups of Streptococci we discussed (on the chart)? What do they do?

A
  1. Pyogenic strep: pus and fever forming
  2. Anginosis strep: abscess forming
  3. Viridans strep: “green”, part of the oral flora, includes Strep. pneumoniae
30
Q

What are the 3 different forms of hemolysis?

A

Alpha: weakly hemolytic, partial, “greening”
Beta: complete hemolysis
Gamma: no hemolysis

31
Q

How many different groups of Strep are there?

A

18

32
Q

S. pyogenes: what is the hemolysis profile, PYR test result, and antibiotic susceptibilities?

A

Beta hemolytic
PYR +
Susceptible to ß-lactams and Bacitracin

33
Q

Why is S. pyogenes susceptibility to Bacitracin important?

A

Because other Strep are resistant to bacitracin

34
Q

What is the PYR test looking for?

A

Tests for the presence of pyrrolidonyl arylamidase (enzyme)

35
Q

Which organisms are positive for the PYR test/which ones are negative?

A

Enterococcus and Gp A Strep +ve

S. bovis and other Streptococci -ve

36
Q

Which population of patients should be screened for Group B strep? Why? What species is an example of this?

A

Pregnant women because infections with group B strep tend to affect neonates

S. Agalactiae is an example

37
Q

What is the hemolysis profile of S. Agalactiae ?

A

Weakly ß hemolytic

38
Q

What is the result of the CAMP test for S. Agalactiae ?

A

Positive

39
Q

What is the CAMP test used for? How does it work? What is a positive result?

A

Differentiates Gp B from otherStreptococci

Synergistic haemolysis observed between S. aureus and Gp B Streptococci

Positive reaction: arrow head haemolysis pattern

40
Q

What is another name for the Streptococcus anginosus group?

A

the milleri group

41
Q

What 3 species are part of the Streptococcus anginosus group?

A

S. anginosus
S. intermedius
S. constellatus

42
Q

What Lancefield group are the Streptococcus anginosus group mainly a part of ?

A

Group F

- some A, G and C though

43
Q

What is the growth/hemolysis profile of the Streptococcus anginosus group?

A

Pinpoint colonies with ß hemolysis

44
Q

What does the Streptococcus anginosus group smell like when grown in culture?

A

Butterscotch

45
Q

What pathology is the Streptococcus anginosus group associated with?

A

Deep seated brain abscesses

46
Q

What 4 related species make up the Strep. bovis group?

A

S. equinus, S. gallolyticus, S. infantarius, and S. alactolyticus

47
Q

What Lancefield group are the S. bovis group part of?

A

Group D

48
Q

What typically harsh conditions are the S. bovis group members capable of growing in?

A

Bile

49
Q

What specific test is the S. bovis group members positive for?

A

Esculin bile test +

50
Q

What two features of Enterococci differentiates them from the S. bovis group ?

A

they are PYR + and can grow in 6.5% NaCl

51
Q

What two tests are used to differentiate S. pneumoniae from the other Viridans strep? What are the results ?

A

Optochin test and bile solubility

S. pneumoniae is sensitive to Optochin and soluble in bile

other viridans strep are Optochin resistant and insoluble in bile

52
Q

All viridans strep members display what kind of hemolysis?

A

Alpha

53
Q

What group of Strep are biochemically similar to the Viridans group?

A

Nutritionally variant strep

54
Q

What is the testing/hemolysis profile of nutritionally variant strep (optochin, bile, PYR)

A

Optochin resistant
Bile insoluble
PYR+
Alpha hemolytic

55
Q

What do the nutritionally variant strep require for growth ?

A

PYRIDOXAL (vitamin B6)

56
Q

What are 2 gram positive bacilli?

A

Listeria monocytogenes and Corynebacterium

57
Q

What are two tests that listeria is positive for?

A

CAMP and Catalase positive

58
Q

What is the hemolysis pattern of listeria?

A

ß-hemolytic

59
Q

What is listeria intrinsically resistant to ?

A

Cephalosporins

60
Q

What is the classic gram stain depiction of Corynebacterium?

A

Chinese lettering

61
Q

What test is Corynebacterium positive for?

A

Catalase

62
Q

What are 3 pathogenic species of Corynebacterium?

A

C. diphtheriae
C. pseudodiptheriticum
C. urealyticum

Clinical Micro (28 decks)

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