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2.2 Microbiology > Staphylococcus Species > Flashcards

Staphylococcus Species Flashcards

(53 cards)

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1
Q

Give the preliminary ID Tests for staphylococci
(3)

A

Gram positive

Cocci

Catalase +

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2
Q

How do you speciate staphylococci?
(3)

A

Coagulase test

+ = S. aureus

  • = S. epidermidis or saprophyticus
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3
Q

What are the three clinically significant species of staphylococci

A

S.aureus

S. epidermidis

S. saprophyticus

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4
Q

What is a gram positive cocci but catalase negative species

A

Micrococcaceae

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5
Q

How many genera of staphyloccaceae are there

A

6

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6
Q

What is the most clinically significant micrococcaceae

A

Micrococcus

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7
Q

How are staphylococci arranged?

A

Grape like clusters

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8
Q

How many species of staphylococci are there?

A

40+

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9
Q

Why are there only a few species of staphylococci that are considered clinically significant

A

Most species only exist as commensals

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10
Q

Name four species of commensal staphylococci that have some varying pathogenic potential

A

S. aureus

S. epidermidis

S. saprophyticus

S. haemolyticus

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11
Q

What clinical specimens can staphylococcus be found in?
(6)

A

Skin wab
Pus specimen
Wound swab
Blood - blood cultures for BSI
Sputum
Urine

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12
Q

What must be done with specimens potentially containing staph
(2)

A

MRSA surveillance to detect carriage

Screening swabs can be taken from the nasal, axilla groin or carriage

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13
Q

In general what are the growth characteristics of staph?

A

Facultative aerobe
Halophilic

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14
Q

What does halophilic mean?

A

Can grow in NaCl as high as 15%

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15
Q

What is query staph put up on on day 1 of investigation
(4)

A

General purpose: Blood agar

Selective agar
- Mannitol salt agar
- Chromogenic media e.g. S. aureus ID or CHROMagar MRSA

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16
Q

How should you incubate staphylococcus on blood agar?

A

Incubate at 37 degrees for 24 hours

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17
Q

How should you incubate the selective and differential medias for Staphylococci?

A

Incubate for 24-48 hours at 37 degrees Celsius

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18
Q

What are the selective agents of Mannitol Salt agar and how do they work?

A

7.5% salt

High salt favours growth of salt-tolerant Staphylococcus species

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19
Q

What are the differential agents of mannitol salt agar and how do they work?
(3)

A

Mannitol is the differential agent

S. aureus can ferment mannitol producing yellow colonies

S. epidermidis cannot ferment mannitol and will grow as pink or white colonies

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20
Q

List the Chromogenic Mediums that can be used for Staphylococci
(3)

A

Oxoid Chromogenic MRSA Agar

BioMérieux Chrome ID

ChromID MRSA

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21
Q

How does Oxoid Chromogenic MRSA Agar work?
(3)

A

Chromogens detect phosphatase activity in S. aureus -> this will produce denim-blue colonies

Cefoxitin (methicillin) will inhibit MSSA colonies

This allows for the accurate detection of MRSA

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22
Q

How does the BioMérieux- Chrome ID work?
(3)

Study These Flashcards
A

SAID -> S. aureus ID

Chromogens detect alpha glucuronidase in S. aureus

This forms green colonies i.e. S, aureus = green colonies

23
Q

How does the ChromID MRSA agar work?

Study These Flashcards
A

MRSA stains indicated by green colonies

Results from alpha-glucuronidase producing colonies in the presence of cefoxitin

24
Q

How does the ChromID MRSA agar work?
(2)

Study These Flashcards
A

MRSA stains indicated by green colonies

Results from alpha-glucuronidase producing colonies in the presence of cefoxitin

25
What tests are carried out on Day 2 to identify Staphylococcus? (9)
Colonial morphology Gram stain -> GPC, grape-like clusters Catalase positive Coagulase Protein A DN'ase Biochemical profile - Vitek/Phoenix Protein profile - MALDI Molecular ID systems - Real Time PCR
26
What are the four classifications of tests carried out on day 2 for the identification of an organism
Basic characterisation tests Manual Conventional confirmatory tests Automated conventional confirmatory tests Molecular confirmatory tests
27
What manual conventional confirmatory tests are carried out for Staphylococcus (3)
Coagulase Protein A DN'ase
28
What automated conventional confirmatory tests are carried out for staphylococcus?
Biochemical profile on the Vitek/Phoenix Protein profile on the MALDI
29
What molecular confirmatory tests are carried out for Staphylococcus?
Molecular ID systems - Real Time PCR
30
What is the definitive test to identify S. aureus?
Coagulase test Test for the detection of coagulase enzyme
31
What are the two ways of carrying out coagulase test?
Slide coagulase/clumping factor test Tube method
32
What is the slide coagulase/clumping factor test and how do you carry it out?
Detects bound coagulase only Mix bacterial saline suspension with rabbit plasma (source of fibrinogen), observe agglutination
33
What is the slide coagulase/clumping factor test and how do you carry it out?
Detects bound coagulase only Mix bacterial saline suspension with rabbit plasma (source of fibrinogen), observe agglutination
34
What is the tube method of coagulase test and how is it carried out?
Detects free and bound coagulase Mix 9 drops of 3hr incubated test suspension with 1 drop rabbit plasma -> incubate over night -> observe clot
35
What does a positive coagulase test mean?
This is sufficient to identify S. aureus
36
What does a negative coagulase mean?
Coagulase negative staphylococcus species These are collectively called CNS
37
What is the most common way of detecting coagulase
Staphaurex Plus
38
What is Staphaurex Plus
Rapid latex agglutination test for the identification of S. aureus
39
Why should Staphaurex be used instead of methods of testing for coagulase? (3)
In addition to coagulase, protein A is also found on the surface of 95% of human strains of S. aureus Certain MRSA possess a capsule that masks both protein A and the coagulase With Staphaurex, rapid agglutination will occur using any three of these components
40
What will cause rapid agglutination in the Staphaurex Plus test? (3)
Reaction between fibrinogen and coagulase Binding between Protein A and the Fc portion of IgG Binding between MRSA capsular polysaccharide and specific IgG
41
Explain in your own words how the Staphaurex Plus test works (4)
Test latex beads are coated in porcine fibrinogen which will detect coagulase Latex bead also coated with IgG antibodies IgG anti capsular polysaccharide to detect MRSA capsule Fc portion of IgG will detect Protein A
42
What is the DN'ase test?
Deoxyribonuclease Agar Nutrient agar that has 0.2% DNA added
43
How is DN'ase agar used? (5)
Spot inoculate DNase agar and incubate overnight Flood with 1 molar HCL HCL precipitates DNA which turns the medium cloudy DNase-positive cultures -> DNA is unavailable for precipitation so there will be a clear zone around the inoculum e.g. S. aureus DNase negative will have no zone of clearing e.g. CNS
44
What automation is used in the identification of Staphylococcus (5)
VITEK GP Card - biochemical reactions MALDI-TOF -> protein profile These are used to ID S. aureus and speciate Coagulase negative staff if it's required Molecular ID systems- real time PCR detection systems such as the Xpert MRSA/SA assay can be used - these target protein A (SA) or mecA (meth resistance) DNA sequences - mostly used in MRSA surveillance for direct screening or confirmation of MRSA from nasal swabs
45
How does the Xpert MRSA/SA assay work? (2)
Molecular ID system which uses real-time PCR It detects targets such as Protein A (found in S. aureus) or mecA (found in methicilin resistant strains) DNA sequences
46
When is the Gene Xpert used for Staphylococci
Used in MRSA surveillance -> for direct screening or confirmation of MRSA from nasal swabs
47
What test do you carry out on Coagulase negative staph to speciate them?
Automated VITEK/MALDTOF Novobiocin resistance
48
How do you carry out the novobiocin test, what are the results (4)
Nutrient agar with novobiocin discs Lawn inoculum S. aureus/CNS are novobiocin susceptible S. saprophyticus are novobiocin resistant
49
How is methicillin susceptibility performed?
Using cefoxitin
50
What are the three classifications of S. aureus infection
Superficial infection Serious infection with S. aureus Serious infection with MRSA
51
How is a superficial staph infection treated?
Topical = mupirocin Oral = augmentin
52
How is a serious infection with S. aureus treated?
Requires aggressive treatment including incision and drainage of lesions Systemic antibiotic needed = Methicillin
53
How is a serious infection with MRSA treated?
Aggressive treatment including incision and drainage of lesions Systemic antibiotic = Vancomycin

2.2 Microbiology (60 decks)

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