[2S] Exp 8 & 9 AT & Test for AR Flashcards by JULIA CASSANDRA RECCION

AST : KIRBY-BAUER DISK DIFFUSION

T/F: Once agent has been identified & deemed as clinically significant = proper selection of antimicrobial agents is performed

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Provide MIC (minimum inhibitory concentration) values or zones of inhibition established using cut-off
points/break off

Kirby-Bauer Disk Method

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AST : KIRBY-BAUER DISK DIFFUSION

Spreading of bacteria on an agar plate and placing paper discs impregnated with antibiotics on the plate

Disk Diffusion

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AST : KIRBY-BAUER DISK DIFFUSION

Area around antibiotic disk where no bacterial growth can be seen

Zone of Inhibition

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AST : KIRBY-BAUER DISK DIFFUSION

Zone indicates?

antibiotic is successful in stopping bacterial growth or killing bacteria

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AST : KIRBY-BAUER DISK DIFFUSION

Diameter is measured to?

compare efficacy of antibiotics and monitor antimicrobial resistance

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AST : KIRBY-BAUER DISK DIFFUSION

Specimen used

< 24 hour-old test culture on BAP, TSA or NAP

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AST : KIRBY-BAUER DISK DIFFUSION

Turbidity of suspension is visually compared to

0.5 McFarland standard

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AST : KIRBY-BAUER DISK DIFFUSION

Turbidity of inoculum is adjusted by

Adding sufficient sterile saline or adding more colonies

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AST : KIRBY-BAUER DISK DIFFUSION

Desired turbidity of the inoculum

same turbidity with McFarland Standard

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AST : KIRBY-BAUER DISK DIFFUSION - INOCULATION OF MHA PLATE

Material used to dip in standardized inoculum suspension

Sterile cotton swab

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AST : KIRBY-BAUER DISK DIFFUSION - INOCULATION OF MHA PLATE

Excess fluid in cotton swab

Pressed and rotated multiple times against wall of test tube

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AST : KIRBY-BAUER DISK DIFFUSION - INOCULATION OF MHA PLATE

Manner of streaking (surface medium)

Inoculated by overlap method of streaking

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AST : KIRBY-BAUER DISK DIFFUSION - INOCULATION OF MHA PLATE

Rotate plate ___ each time for even distribution

60°

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AST : KIRBY-BAUER DISK DIFFUSION - INOCULATION OF MHA PLATE

T/F: After streaking, rim-edge the medium

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AST : KIRBY-BAUER DISK DIFFUSION - INOCULATION OF MHA PLATE

Number of times plate is rotated

3-4x to ensure that it’s confluent

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AST : KIRBY-BAUER DISK DIFFUSION - INOCULATION OF MHA PLATE

Inoculation is done [time] from time of standard inoculum was prepared

<15 minutes

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AST : KIRBY-BAUER DISK DIFFUSION - INOCULATION OF MHA PLATE

Place ___ then apply antibiotic disks

3-5 minutes

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AST : KIRBY-BAUER DISK DIFFUSION - APPLICATION OF ANTIBIOTIC DISKS

Place disks evenly distributed
o At least ____ from each other
o At least ____ from edge of the plate

24mm
10mm

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AST : KIRBY-BAUER DISK DIFFUSION - APPLICATION OF ANTIBIOTIC DISKS

Plates are inverted and placed in incubator set at ____ for _____

35-37C; 16-18 hours

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Uses standardized amount of test inoculum present in Mueller Hinton Broth (MHB) and a selected antimicrobial agent

Broth Dilution

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AST : BROTH MACRODILUTION OR
MACROBTROTH DILUTION

Medium used

Mueller Hinton Broth (MHB)

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AST : BROTH MACRODILUTION OR
MACROBTROTH DILUTION

Antimicrobial agent is diluted ___-fold

two

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AST : BROTH MACRODILUTION OR
MACROBTROTH DILUTION

Lowest concentration of antimicrobial agent that
completely inhibits visible growth

MIC

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AST : BROTH MACRODILUTION OR MACROBTROTH DILUTION Interpretative categories

o Susceptible (S) o Intermediate (I) o Resistant (R)

AST : BROTH MACRODILUTION OR MACROBTROTH DILUTION 2 categories

Broth microdilution & Broth macrodilution

AST : BROTH MACRODILUTION OR MACROBTROTH DILUTION Main difference of the 2 categories

volume of the MHB used

AST : BROTH MACRODILUTION OR MACROBTROTH DILUTION Specimen used

Culture on BAP

AST : BROTH MACRODILUTION Final Bacterial Concentration

5x10^5 CFU/mL

AST : BROTH MACRODILUTION Adjusted inoculum is diluted _____ by adding 0.1mL of standardized inoculum in 19.9 mL MHB

1:200

AST : BROTH MACRODILUTION Test tube 1-10 is for

actual test

AST : BROTH MACRODILUTION How many test tubes are needed?

13 sterile test tubes

AST : BROTH MACRODILUTION Test tube 12 is for

Broth Control (BC)

AST : BROTH MACRODILUTION Test tube 11 is for

Inoculum Control (IC)

AST : BROTH MACRODILUTION Test tube 13 is for

Antibiotic Control (AC)

AST : BROTH MACRODILUTION Incubate ____ ambient air for ____

35-37°C; 18-24 hrs

AST : BROTH MACRODILUTION Growth on control tube 11

Visible growth

AST : BROTH MACRODILUTION Growth on control tube 12 & 13

No visible growth

AST : BROTH MACRODILUTION determine tube with lowest antibiotic concentration with no visible growth

MIC

DETERMINATION OF MBC T/F: Pipette 1 mL from each tube showing no visible growth and subculture to agar plates

F; 0.01 mL

DETERMINATION OF MBC T/F: After pipetting 0.01 mL from each tube showing no visible growth to agar plates, incubate 18-24 hrs at 35-37°C ambient air

AST : BROTH MACRODILUTION lowest antibiotic concentration that results in 99% killing

MBC

AST : BROTH MACRODILUTION Determined by identifying the plate with lowest antibiotic concentration showing no visible growth

MBC

Due to different external and internal factors that prevent the action of antimicrobials

Antibiotic Resistance

TEST FOR ANTIMICROBIAL RESISTANCE Cleaves beta lactam ring of penicillin and cephalosporins

Beta lactamase enzyme

TEST FOR ANTIMICROBIAL RESISTANCE Detected in Gr (+) & Gr (-) Bacterias

Beta Lactamase

TEST FOR ANTIMICROBIAL RESISTANCE

TEST FOR BETA LACTAMASE Bacterias detected

o Staphylococcus o H. Influenzae o N. gonorrhoeae

TEST FOR BETA LACTAMASE 3 Methods used

Iodometric Acidimetric Chromogenic

TEST FOR BETA LACTAMASE

TEST FOR BETA LACTAMASE Most sensitive method

Chromogenic

TEST FOR BETA LACTAMASE Positive result

Color change from yellow to red

TEST FOR BETA LACTAMASE Bacteria that take up to 1 hr to develop a color change

Staphylococcus

TEST FOR BETA LACTAMASE Specimen

Culture of Staphylococcus growing in BAP or TSA

TEST FOR ANTIMICROBIAL RESISTANCE For determining MRSA

Cefoxitin Screen Test

CEFOXITIN SCREEN TEST PROCEDURE Streak standardized inoculum using _________

Disk Diffusion Method

TEST FOR ANTIMICROBIAL RESISTANCE Excellent induced or mecA gene

Cefoxitin

TEST FOR ANTIMICROBIAL RESISTANCE Code for PBP2a responsible for methicillin and oxacillin resistance

mecA gene

CEFOXITIN SCREEN TEST Specimen

Culture of Staphylococcus aureus in BAP or TSA

CEFOXITIN SCREEN TEST PROCEDURE Place a __ ug cefoxitin disk at the center

CEFOXITIN SCREEN TEST PROCEDURE Measure zone inhibition of S. aureus ≥ 22 mm

Susceptible

CEFOXITIN SCREEN TEST PROCEDURE Incubate plate at ___. Do not incubate above __

30-35°C

CEFOXITIN SCREEN TEST PROCEDURE Measure zone inhibition of S. aureus ≤ 21 mm

Resistant

AST uses plastic strip

E-test

AST uses paper strip

Liofilchem

AST Quantitative assay for determining MIC

E-test

AST E-test test strip is applied onto?

an inoculated agar surface

AST : GRADIENT DIFFUSION – E-TEST T/F: After 18 hours incubation or longer, a symmetrical inhibition ellipse centered along the strip is formed

AST Preformed exponential gradient of antimicrobial agent is transferred into the agar matrix

Test Strip

AST : GRADIENT DIFFUSION – E-TEST E-test specimen

Culture on BAP

AST : GRADIENT DIFFUSION – E-TEST Medium used

Mueller-Hinton Broth

AST : GRADIENT DIFFUSION – E-TEST Streak the standardized inoculum using the [technique]?

Overlapping Streaking Technique

AST : GRADIENT DIFFUSION – E-TEST Apply the strip to the agar surface with the scale facing _______ and code of the strip to the outside of the plate

upwards

AST : GRADIENT DIFFUSION – E-TEST Set up time

<5 minutes

AST : GRADIENT DIFFUSION – E-TEST T/F: The antibiotic gradient should be in complete contact with the agar surface

AST : GRADIENT DIFFUSION – E-TEST Time to Result

16-20 hrs

AST : GRADIENT DIFFUSION – E-TEST T/F: Strip can be repositioned within 5 minutes from its application

F; 3 mins

AST : GRADIENT DIFFUSION – E-TEST Consult the?

MIC Test Strip Photographic Guide

AST : GRADIENT DIFFUSION – E-TEST Indicates that the value is greater than or equal to (≥) the highest value on the scale

Growth along the entire gradient i.e. no inhibition ellipse

AST : GRADIENT DIFFUSION – E-TEST An inhibition ellipse that intersects below the lower end of the scale is read as _______ the lowest value

less than (<)

AST : GRADIENT DIFFUSION – E-TEST T/F: Observe where the relevant inhibition ellipse intersects the strip and read the MIC at complete inhibition