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Bacteriology Exam 3 (Staph vs Strep) 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
staph epidermidis
catalase positive, coagulase negative, weakly or non-hemolytic
26
what is staph saprophyticus associated with?
UTIs in young women
27
which staph is known to contain the mecA gene? (MRSA)
staph lugdunensis
28
which staph is positive for clumping factor but negative for coagulase?
S. lugdunensis
29
Where is micrococcus found? How can this be differentiated from staphylococcus by fermentation and motility?
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
30
What is the traditional culture and workup to identify a species?
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
31
Micrococcus hemolysis pattern
non-hemolytic (gamma)
32
beta-hemolytic staph
s. aureus, s. haemolyticus, sometimes s. lugdunensis
33
Special agar used for MRSA
CHROMagar (pink/mauve color is positive for MRSA organism)
34
what does a slide coagulase test show the presence of?
bound coagulase/clumping factor
35
what is tube coagulase detecting?
free coagulase/extracellular
36
What does the staphyloslide test/bound coagulase test detect?
clumping factor and protein A (characteristic of S. aureus)
37
What does lysostaphin and microdase testing help differentiate? Which is positive (lysostaphin resistant) and which is negative (lysostaphin susceptible)?
Micrococcus sp. which is lysostaphin positive/microdase positive and staphyloccocus sp. which is lysostaphin negative/microdase negative
38
Is staph bacitracin sensitive or resistant? Micrococcus?
Staph is bacitracin resistant. Micrococcus is bacitracin sensitive
39
mecA positive strains are considered resistant to all ________.
penicillins
40
msrA gene
resistant erythromycin will not induce clindamycin resistance
41
erm gene
resistant erythromycin will induce clindamycin resistance
42
what is used to screen for MRSA?
Cefoxitin disks (PB2a testing), Chromogenic selective differential media
43
What is the drug of choice for MRSAs?
Vancomycin
44
What are false positives associated with coagulase testing?
GNR (which is why you do gram stain before coagulase) S. intermedius (dog bite wounds) S. saphrophyticus, S. haemolyticus, S. hominis
45
What streptococcus species are almost always pathogens?
Strep pyogenes, Strep pneumonia, and Enterococcus
46
All streptococci are LAP _______
positive
47
Hemolytic pattern for streptococcus sp.
Varies - can be alpha beta or gamma
48
Pyogenic streptococcus hemolysis
beta
49
Enterococcus species hemolysis
gamma or alpha
50
Enterococcus is PYR ______
positive
51
What streptococci group is not part of the Lancefield group?
Viridans streptococci
52
Lancefield Group A streptococci
Streptococcus pyogenes
53
Lancefield group B streptococci
Streptococcus agalactiae
54
Lancefield group C streptococci
Streptococcus equi, Streptococcus dysgalactiae
55
Lancefield Group D strep
Enterococcus faecalis, Enterococcus faecium, Enterococcus durans and Streptococcus bovis
56
Lancefield Group F, G & L streptococcus
Streptococcus anginosus or S. dysgalactiae
57
What kind of hemolysis pattern do you do Lancefield typing on?
Beta hemolysis only
58
What are the two most common enterococcus associated with human infections?
E. faecalis and E. faecium
59
Pyogenic streptococci vs non-pyogenic streptococci
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
Streptococcus pyogenes virulence factors
Protein F - epithelial cell attachment Streptolysin O, S, Streptokinase, Hyaluronidase - tissue invasion and destruction SPEs - mediate production of rash
61
Streptolysin O
virulence factor found in strep pyogenes that is oxygen unstable and only lyses cells when oxygen is not present
62
Streptolysin S
virulence factor in strep pyogenes that is oxygen stable and only lyses cells when oxygen is present
63
What is responsible for strep pyogenes beta hemolytic pattern?
Streptolysin O and Streptolysin S
64
What clinical infections does strep pyogenes cause?
Bacterial pharyngitis (strep throat) Skin infections - scarlet fever Type 2 necrotizing fasciitis Toxin Shock Syndrome
65
Poststreptococcal sequelae complications
Rheumatic fever following strep throat Acute glomerulonephritis after throat infection
66
Drug of choice for strep pyogenes infection
Penicillin or erythromycin
67
Strep pyogenes PYR, LAP, CAMP, and Bacitracin results
PYR positive LAP positive CAMP negative Susceptible to bacitracin
68
Where is strep agalactiae normally found?
female genital tract
69
Where are infections of strep agalactiae normally found and in which patients?
Vaginal - Normally found in neonates and infants from childbirth processes
70
Drug of choice for strep agalactiae infections
Penicillin
71
Strep agalactiae hemolysis pattern, bacitracin result, CAMP, PYR and hippurate
Beta hemolytic (4% gamma hemolytic) Bacitracin resistant CAMP positive PYR negative Hippurate positive
72
Which strep shows a positive classic arrowhead result for CAMP tests?
Strep agalactiae
73
What would you expect to see on a gram stain for S. pneumoniae?
Gram positive cocci (LANCET shaped) in pairs or chains
74
What does S. pneumoniae look like on a culture (specific characteristic of their colonies)?
they have a cratered center
75
What does S. pneumoniae grow best with?
5-10% CO2
76
What is the drug of choice for S. pneumoniae?
Penicillin if antibiotic resistance is not present
77
What is S. pneumoniae associated with infection-wise?
Bacterial meningitis (CSF-related diseases) Respiratory diseases (pneumonia)
78
Viridans strep are _______ and some require CO2 to grow.
fastidious
79
Viridans strep hemolysis and notable features on culture
most are gamma hemolytic (some are alpha) and colonies may smell like butterscotch
80
Viridans Strep includes which group?
Bovis group (group D)
81
Why are viridans strep not groupable by Lancefield serology?
They do not have carbohydrate antigens on the cell surface
82
Viridans Strep - are they normal flora? which diseases may they cause?
Usually normal flora and are not highly invasive. Most common cause of sub-acute bacterial endocarditis (SBE)
83
Viridians Strep - LAP, PYR, BE, Salt growth results
LAP positive PYR negative BE negative Do not grow with salt
84
How do you differentiate S. pneumoniae from S. viridans?
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
What can enterococcus cause?
UTIs, bacteremia, or skin/wound infections
86
What two species express the group D antigen?
Enterococcus sp. and S. bovis
87
E. faecalis and E. faecium differentiate on a plate
E. faecalis is larger colonies with gamma hemolysis E. faecium is smaller and darker colonies with alpha hemolysis
88
Enterococcus: PYR, BE, LAP, Salt growth, Catalase
PYR positive BE positive LAP positive Able to grow in salt Catalase negative
89
Vancomycin resistance in Enterococcus sp. (what genes do they have causing this)
E. faecium - has VanA and VanB genes
90
What steps would you take to differentiate S. bovis group from Enterococcus sp.?
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
Nutritionally variant strep - why do they not grow? What would we grow them on?
Abiotrophia and Granulicatella are notable genera that require Vitamin B6 supplied in vitro.
92
Aerococcus sp. gram stain
GPC in tetrads/clusters
93
What are the main two species that are PYR positive?
S. pyogenes and Enterococcus sp.

Microbiology (24 decks)

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