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Bacteriology > AST PT.2 > Flashcards

AST PT.2 Flashcards

1
Q

Kirby Bauer Method Test Performance/Procedure
Disk Storage:
Working Supply (1week): 1.
Stocks (Long Term): 2.
Store in a tightly sealed container with dessicant
* Culture Medium: 3
 May be supplemented with 4. or other nutrients

A
  1. 2-8C
  2. -20C in a non frost freezer
  3. Mueller Hinton
  4. 5% sheep blood
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2
Q

Kirby Bauer Method Test Inoculum and Inoculation:

0.5 McFarland Standard Inoculum
* 1. is dipped onto the inoculum and swabbed evenly on the culture medium
* 2. mm diameter 3. plate is used
 It can accommodate up to 4. antibiotic disks
* After __ minutes, the disks are then placed

A
  1. Sterile Cotton Swab
  2. 150
  3. MHA (Mueller hinton agar)
  4. 12
  5. 15 mins
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3
Q

Advantages of Kirby Bauer Method

A

convenient and user friendly

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4
Q

Disadvantages of Kirby Bauer Method

A
  • Not all organisms have interpretative criteria
  • Unable to provide more precise data about the level of resistance
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5
Q

Determine Minimum Inhibitory Concentration (MIC)
* Use of serial 2-fold dilutions of the antimicrobial agent (expressed as ug or mcg/ml)
* Once MIC is determined, it is interpreted as S, I, R

A

DILUTION SUSCEPTIBILITY TESTING

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6
Q

DILUTION SUSCEPTIBILITY TESTING Principle
* Standard Culture: _
* Final Standard Bacterial Inoculum: ___

A

MHA( Mueller Hinton agar), 5x10^5 CFU/ml

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7
Q
  • Challenging the organism with antimicrobial agents in a liquid environment
  • Use of different range of antimicrobial agent concentrations
    Determination of MIC (Minimal Inhibitory Concentration)
A

DILUTION SUSCEPTIBILITY TESTING

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8
Q

Prepared from reference standard antimicrobial powders

A

Stock Solutions

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9
Q

What is the storage for DST: Stock solutions?

A

-60C

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10
Q

Use of test tubes
Volume: 1-2 ml

A

Macrodilution

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11
Q

Use of wells
Volume: 0.05-0.1ml

A

Microdilution

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12
Q
  • The first tube or well showing no visible bacterial growth is the MIC
  • Maximum of Number of Disks per 150mm diameter plate: 12 disks
  • Culture Plates should not be stacked more than 5 plates high
A

Broth Dilution

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13
Q

Antimicrobial Concentrations and organisms to be tested are placed together on an agar medium (Spot inoculation)
Series of dilutions, with one dilution per plate
Standard Inoculum: 1x104 CFU
MIC: lowest concentration of an antimicrobial agent in agar that completely inhibits visible growth

A

Agar Dilution

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14
Q

Broth Microdilution Methods

A

BBL Sceptor, MicroScan touch SCAN-SR

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15
Q

Agar Dilution Derivations

A

Spiral Biotech

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16
Q

Diffusion in Agar Derivatio

A

E-test: Gradient Diffusion Susceptibility Test

17
Q
  • Establishment of an antimicrobial density gradient
    Uses thin plastic strips (with gradations) placed in a radial fashion on an inoculated plate.
    Interpretation: MIC is read wherein the growth ellipse intersects the Etest strip
    Useful for fastidious organisms
A

E-test

18
Q

Test for the presence of Beta-lactamas

A

Phenotypic Methods

19
Q

Use of filter paper disks impregnated with nitrocefin

Moisten with water or NSS and add a loopful of the colony onto the disk

 (+) Result: RED COLORATION

A

Cephalosporinase test (Cefinase Test)

20
Q

other methods for Beta-lactamse

A

Iodometric
Acidometric Methods

21
Q

Determination of chloramphenicol resistance

A

Chloramphenicol Acetyltranferase Detection

22
Q

Detection of Methicillin (Oxacillin) resistant S. aureus

A

Use of chromogenic agar (ex. CHROM Agar)
For Reliable Detection: MIC
MIC of >/= 4ug/ml (Oxacillin) = MRSA

23
Q

VRSA
VISA

A

Vancomycin Resistance in Staphylococcus

24
Q

Inducible Clindamycin Resistance Test)

A

D-zone test – for Staphylococcus

25
Q

Molecular Methods to determine presence of resistant genes

*Detection of mecA gene and Detection of vanA gene

A

Genotypic Methods

26
Q

– gold standard for confirmation of phenotypic oxacillin resistance
* Latex Agglutination Test
*Molecular Methods

A

Detection of mecA gene

27
Q

Tests that Predict Effectiveness of Therapy

A
  • MIC
  • Disk Diffusion
  • Etest
  • Growth Curve Calculation

Bacteriology (3 decks)

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