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Microbiology > Bacteriology Exam 3 (Staph vs Strep) > Flashcards

Bacteriology Exam 3 (Staph vs Strep) Flashcards

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Biology 101 flashcards
1
Q

Catalase Positive GPC

A

Staphylococcus, Micrococcus, Aerococcus

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2
Q

Catalase Negative GPC

A

Streptococcus, Enterococcus

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3
Q

Novobiocin Resistant Staphylococcus

A

Staph saphrophyticus

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4
Q

Novobiocin Susceptible Staphylococcus

A

S. aureus, Staph epidermidis, Staph haemolyticus, Staph hominis, Staph lugdunensis

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5
Q

If I have a catalase positive organism, is it indicating Staph or Strep? What is the next steps?

A

Catalase positive –> Coagulase Test
Coagulase Positive –> Staph aureus
Coagulase Negative –> Novobiocin testing

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6
Q

T/F: Mostly all Staphylococcus species are normal flora.

A

True

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7
Q

Unique Features for Staphylococcus

A

Catalase Positive, Non-motile, non-spore forming, white/creamy colony with variable beta hemolysis

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8
Q

What bacterial infections are the leading cause of infections in US healthcare facilities?

A

Staph infections

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9
Q

Where is staph aureus primary resorvoir?

A

Nose

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10
Q

What types of coagulase does staph aureus form?

A

Bound and free coagulase

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11
Q

What type of hemolysis does staph aureus have?

A

Beta hemolytic

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12
Q

What cytolytic toxins does staph aureus have? What do they lyse?

A

alpha-hemolysin: lyses RBC
gamma-hemolysin: lethal to WBC

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13
Q

Name 3 mechanisms of virulence that staph aureus has

A

Capsule - prevents phagocytosis and opsonizatioon
Coagulase - helps prevent phagocytosis
Hyaluronidase - hydrolyzes hyaluronic acid

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14
Q

What diseases can staph aureus cause?

A

Toxic Shock Syndrome, sepsis, folliculitis, Scaled Skin Syndrome, Impetigo, skin infections

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15
Q

What is staph aureus virulence factor TSST-1 associated with?

A

toxic shock syndrome

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16
Q

What is staph aureus Exfoliative Toxins cause?

A

Ritter disease AKA scalded skin syndrome and Bullous Impetigo

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17
Q

What bacteria can cause folliculitis, furuncles, carbuncles, and bullous impetigo?

A

staph aureus

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18
Q

Staph aureus enterotoxins

A

contains enterotoxins A, D, and B that can cause food poisoning

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19
Q

Toxic Epidermal Necrolysis (TEN)

A

caused by staph aureus; similar to scalded skin syndrome

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20
Q

What can staphylococcal bacteremia/sepsis lead to?

A

secondary pneumonia and endocarditis among IV drug users

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21
Q

Staphylococcal pneumonia

A

can occur secondary to influenza viral infection

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22
Q

Osteomyelitis (septic arthritis)

A

caused by S. aureus; occurs secondary to bacteremia

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23
Q

Coagulase negative staph

A

S. epidermidis, S. haemolyticus, S. lugdenensis, S. saprophyticus

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24
Q

coagulase negative staph pathogenicity (what are they attributed to in hospital-aquired infections)

A

epidermidis - blood cultures/medical devices
haemolyticus and lugdenensis - medical devices
saprophyticus - UTI in young females

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25
Q

staph epidermidis

A

catalase positive, coagulase negative, weakly or non-hemolytic

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26
Q

what is staph saprophyticus associated with?

A

UTIs in young women

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27
Q

which staph is known to contain the mecA gene? (MRSA)

A

staph lugdunensis

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28
Q

which staph is positive for clumping factor but negative for coagulase?

A

S. lugdunensis

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29
Q

Where is micrococcus found? How can this be differentiated from staphylococcus by fermentation and motility?

A

Micrococcus is found in the environment and normal skin flora
It does not ferment glucose, while staph does ferment glucose.
Micrococcus is motile, staph is non-motile

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30
Q

What is the traditional culture and workup to identify a species?

A
  1. Culture on BAP for hemolysis, CHOC, and selective agars (MAC/CNA)
  2. Look at colony morphology
  3. Gram staining
  4. Catalase and coagulase testing
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31
Q

Micrococcus hemolysis pattern

A

non-hemolytic (gamma)

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32
Q

beta-hemolytic staph

A

s. aureus, s. haemolyticus, sometimes s. lugdunensis

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33
Q

Special agar used for MRSA

A

CHROMagar (pink/mauve color is positive for MRSA organism)

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34
Q

what does a slide coagulase test show the presence of?

A

bound coagulase/clumping factor

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35
Q

what is tube coagulase detecting?

A

free coagulase/extracellular

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36
Q

What does the staphyloslide test/bound coagulase test detect?

A

clumping factor and protein A (characteristic of S. aureus)

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37
Q

What does lysostaphin and microdase testing help differentiate? Which is positive (lysostaphin resistant) and which is negative (lysostaphin susceptible)?

A

Micrococcus sp. which is lysostaphin positive/microdase positive and staphyloccocus sp. which is lysostaphin negative/microdase negative

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38
Q

Is staph bacitracin sensitive or resistant? Micrococcus?

A

Staph is bacitracin resistant.
Micrococcus is bacitracin sensitive

39
Q

mecA positive strains are considered resistant to all ________.

A

penicillins

40
Q

msrA gene

A

resistant erythromycin will not induce clindamycin resistance

41
Q

erm gene

A

resistant erythromycin will induce clindamycin resistance

42
Q

what is used to screen for MRSA?

A

Cefoxitin disks (PB2a testing), Chromogenic selective differential media

43
Q

What is the drug of choice for MRSAs?

A

Vancomycin

44
Q

What are false positives associated with coagulase testing?

A

GNR (which is why you do gram stain before coagulase)
S. intermedius (dog bite wounds)
S. saphrophyticus, S. haemolyticus, S. hominis

45
Q

What streptococcus species are almost always pathogens?

A

Strep pyogenes, Strep pneumonia, and Enterococcus

46
Q

All streptococci are LAP _______

A

positive

47
Q

Hemolytic pattern for streptococcus sp.

A

Varies - can be alpha beta or gamma

48
Q

Pyogenic streptococcus hemolysis

A

beta

49
Q

Enterococcus species hemolysis

A

gamma or alpha

50
Q

Enterococcus is PYR ______

A

positive

51
Q

What streptococci group is not part of the Lancefield group?

A

Viridans streptococci

52
Q

Lancefield Group A streptococci

A

Streptococcus pyogenes

53
Q

Lancefield group B streptococci

A

Streptococcus agalactiae

54
Q

Lancefield group C streptococci

A

Streptococcus equi, Streptococcus dysgalactiae

55
Q

Lancefield Group D strep

A

Enterococcus faecalis, Enterococcus faecium, Enterococcus durans and Streptococcus bovis

56
Q

Lancefield Group F, G & L streptococcus

A

Streptococcus anginosus or S. dysgalactiae

57
Q

What kind of hemolysis pattern do you do Lancefield typing on?

A

Beta hemolysis only

58
Q

What are the two most common enterococcus associated with human infections?

A

E. faecalis and E. faecium

59
Q

Pyogenic streptococci vs non-pyogenic streptococci

A

Pyogenic streptococci are mostly beta hemolytic and part of the Lancefield typing.
Non-pyogenic streptococci are most alpha/gamma hemolytic and are not part of the Lancefield typing.

60
Q

Streptococcus pyogenes virulence factors

A

Protein F - epithelial cell attachment
Streptolysin O, S, Streptokinase, Hyaluronidase - tissue invasion and destruction
SPEs - mediate production of rash

61
Q

Streptolysin O

A

virulence factor found in strep pyogenes that is oxygen unstable and only lyses cells when oxygen is not present

62
Q

Streptolysin S

A

virulence factor in strep pyogenes that is oxygen stable and only lyses cells when oxygen is present

63
Q

What is responsible for strep pyogenes beta hemolytic pattern?

A

Streptolysin O and Streptolysin S

64
Q

What clinical infections does strep pyogenes cause?

A

Bacterial pharyngitis (strep throat)
Skin infections - scarlet fever
Type 2 necrotizing fasciitis
Toxin Shock Syndrome

65
Q

Poststreptococcal sequelae complications

A

Rheumatic fever following strep throat
Acute glomerulonephritis after throat infection

66
Q

Drug of choice for strep pyogenes infection

A

Penicillin or erythromycin

67
Q

Strep pyogenes PYR, LAP, CAMP, and Bacitracin results

A

PYR positive
LAP positive
CAMP negative
Susceptible to bacitracin

68
Q

Where is strep agalactiae normally found?

A

female genital tract

69
Q

Where are infections of strep agalactiae normally found and in which patients?

A

Vaginal - Normally found in neonates and infants from childbirth processes

70
Q

Drug of choice for strep agalactiae infections

A

Penicillin

71
Q

Strep agalactiae hemolysis pattern, bacitracin result, CAMP, PYR and hippurate

A

Beta hemolytic (4% gamma hemolytic)
Bacitracin resistant
CAMP positive
PYR negative
Hippurate positive

72
Q

Which strep shows a positive classic arrowhead result for CAMP tests?

A

Strep agalactiae

73
Q

What would you expect to see on a gram stain for S. pneumoniae?

A

Gram positive cocci (LANCET shaped) in pairs or chains

74
Q

What does S. pneumoniae look like on a culture (specific characteristic of their colonies)?

A

they have a cratered center

75
Q

What does S. pneumoniae grow best with?

A

5-10% CO2

76
Q

What is the drug of choice for S. pneumoniae?

A

Penicillin if antibiotic resistance is not present

77
Q

What is S. pneumoniae associated with infection-wise?

A

Bacterial meningitis (CSF-related diseases)
Respiratory diseases (pneumonia)

78
Q

Viridans strep are _______ and some require CO2 to grow.

A

fastidious

79
Q

Viridans strep hemolysis and notable features on culture

A

most are gamma hemolytic (some are alpha) and colonies may smell like butterscotch

80
Q

Viridans Strep includes which group?

A

Bovis group (group D)

81
Q

Why are viridans strep not groupable by Lancefield serology?

A

They do not have carbohydrate antigens on the cell surface

82
Q

Viridans Strep - are they normal flora? which diseases may they cause?

A

Usually normal flora and are not highly invasive.
Most common cause of sub-acute bacterial endocarditis (SBE)

83
Q

Viridians Strep - LAP, PYR, BE, Salt growth results

A

LAP positive
PYR negative
BE negative
Do not grow with salt

84
Q

How do you differentiate S. pneumoniae from S. viridans?

A

Optochin (P disk)
S. pneumoniae is susceptible
S. viridians is resistant

Bile solubility
S. pneumoniae is bile soluble
S. viridians is not bile soluble

85
Q

What can enterococcus cause?

A

UTIs, bacteremia, or skin/wound infections

86
Q

What two species express the group D antigen?

A

Enterococcus sp. and S. bovis

87
Q

E. faecalis and E. faecium differentiate on a plate

A

E. faecalis is larger colonies with gamma hemolysis
E. faecium is smaller and darker colonies with alpha hemolysis

88
Q

Enterococcus: PYR, BE, LAP, Salt growth, Catalase

A

PYR positive
BE positive
LAP positive
Able to grow in salt
Catalase negative

89
Q

Vancomycin resistance in Enterococcus sp. (what genes do they have causing this)

A

E. faecium - has VanA and VanB genes

90
Q

What steps would you take to differentiate S. bovis group from Enterococcus sp.?

A

S. bovis is PYR negative, Enterococcus is PYR positive
S. bovis does not grow with salt, enterococcus does grow with salt
S. bovis is susceptible to penicillin, enterococcus is resistant to penicillin

91
Q

Nutritionally variant strep - why do they not grow? What would we grow them on?

A

Abiotrophia and Granulicatella are notable genera that require Vitamin B6 supplied in vitro.

92
Q

Aerococcus sp. gram stain

A

GPC in tetrads/clusters

93
Q

What are the main two species that are PYR positive?

A

S. pyogenes and Enterococcus sp.

Microbiology (24 decks)

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