(Lecture) Antimicrobial Susceptibility Testing Flashcards
A laboratory procedure in which it determines the susceptibility pattern of an isolate
Antimicrobial Susceptibility Testing
Substance that inhibit the growth of microorganisms
Antibiotics
Products of microorganisms that reacts with and inhibit the growth of another microorganism
Antibiotics
This is performed on bacteria causing an individual’s infection after they have been recovered in a culture of the specimen.
Antibiotic Susceptibility Testing
What are the 2 Methods of AST?
Diffusion Method
Dilution Method
It is used to determine the potential effectiveness of specific antibiotics on the bacteria and/or to determine if the bacteria have developed resistance to certain antibiotics.
Antibiotic Susceptibility Testing
List down the methods under Diffusion Methods:
- Kirby-Bauer Diffusion Method
- Agar Cup Diffusion Method
- Agar Cylinder Diffusion Method
- Epsilometer or Gradient Diffusion Method
List down the methods under Dilution Methods:
- Macrobroth Method or Tube Dilution Method
- Microtube Dilution Method
It is a suspension of bacteria that has been isolated from a patient.
Pure Inoculum
Required number of bacteria that must be present in a pure inoculum:
1.5 x 10^8 CFU/mL
Required number of bacteria that must be present in a pure inoculum:
1.5 x 10^8 CFU/mL
This is used to standardize the approximate number of bacteria in a liquid suspension by visually comparing the turbidity of a test suspension with the turbidity of a McFarland standard
Pure Inoculum
Pure Inoculum is used to standardize the approximate number of bacteria in a liquid suspension by visually comparing the turbidity of a test suspension with the turbidity of a _____
McFarland Standard
McFarland Standard is prepared by adding _____ to sulfuric acid to obtain a barium sulfate precipitate
Barium chloride
Pure Inoculum is prepared by adding barium chloride to _____ to obtain a barium sulfate precipitate
Sulfuric acid
Pure Inoculum is prepared by adding barium chloride to sulfuric acid to obtain a _____
Barium sulfate precipitate
Recommended population density:
1.5 x 10^8 CFU/mL
_____ of 1% Sulfuric acid + 0.5 mL of 1.175% Barium chloride
99.5 mL
99.5 mL of _____ Sulfuric acid + 0.5 mL of 1.175% Barium chloride
1%
99.5 mL of 1% Sulfuric acid + _____ of 1.175% Barium chloride
0.5 mL
99.5 mL of 1% Sulfuric acid + 0.5 mL of _____ Barium chloride
1.175%
A tube that has barium chloride and sulfuric acid and it doesn’t have any bacteria.
McFarland Standard
Also known as Agar Diffusion Method or Disk Diffusion Method
Kirby-Bauer Method
Kirby-Bauer Method is also known as _____ or _____
Agar Diffusion Method
Disk Diffusion Method
Principle of Kirby-Bauer Method
- A standardized suspension of organism is inoculated into MHA (Mueller-Hinton Agar)
- Paper disk impregnated with specific antibiotics concentration are placed into the agar
- After 16-20 hours incubation, the diameters of the zone of inhibitions are measured
- Results are compared to determine susceptibility or resistance
A Method wherein you will inoculate the bacteria to the whole surface of culture media without space.
Lawn Culture Method
Kirby-Bauer Method is isolated using _____ - meaning you will inoculate the bacteria to the whole surface of culture media without space. Then put on an antibiotic disc. Each antibiotic disc has different antibiotics.
Lawn Culture Method
The area surrounding the antibiotics wherein it doesn’t have a growth.
Zone of Inhibition
An area with no zone of inhibition is equivalent to _____
6
Lowest Zone of Inhibition Measurement
6
Step-by-Step Procedure for Kirby-Bauer Method
- Preparation of pure inoculum
- Standardize pure inoculum, using 0.5 McFarland Standard
- Streak the pure inoculum into the medium
- Apply antibiotic discs
- Incubate
- Measure the zone of inhibition
In Kirby-Bauer Diffusion Method, we prepare the pure inoculum using the following:
- Mueller-Hinton Broth
- Trypticase Soy Broth
- Sterile Distilled Water
- Natural Saline Solution
- Brain Heart Infusion Broth
If the standard is more turbid than inoculum, what do we do?
Add Colonies or Incubate Inoculum
If the inoculum is more turbid than standard, what do we do?
We add distilled water into the inoculum
A heavy inoculum will result in _____, whereas a lighter inoculum will give _____
Small Zone Sizes
Larger Zone Sizes
A _____ will result in small zone sizes, whereas a _____ will give larger zone sizes
Heavy Inoculum
Lighter Inoculum
In streaking the pure inoculum into the medium, we use _____ and we streak with _____
Sterile Cotton Swab
No Spaces in Between
In applying antibiotic discs, we use _____.
Forceps or Tweezers
Preferred spaces in applying antibiotic discs
At least 25mm each antibiotic
Incubation period for Kirby-Bauer Method
35 degree Celsius for 16/18-20 hours
In measuring the zone of inhibition, what instrument/s is/are used?
Ruler or Microcaliper
Unit used in measuring the zone of inhibition
mm or millimeter
Bacterias are being killed fast. What is the interpretation of the result?
Susceptible or Sensitive
Indicates that the organism is inhibited by the recommended dose, at the infection site of an antimicrobial agent
Susceptible or Sensitive
Represents an organism that may require a higher dose of antibiotic for a longer time period to be inhibited
Intermediate
Antibiotics are not effective for that particular bacteria. This indicates that the microorganisms are _____ to the antibiotics.
Resistant
Organism is not inhibited by recommended dose
Resistant
Considerations in Antimicrobial Susceptibility Testing;
- Growth Medium
- Inoculum
- Temperature and Atmospheric Conditions
- Choice of Antibiotic Panel
- Reading and Interpreting Results
pH required for the Growth of Medium
7.2-7.4
Agar depth required for the Growth of Medium
3-5mm
If the medium is _____ the zones will be falsely small
Too thick
If the medium is too thick the zones will be falsely _____
Small
If the medium is _____ the zones will be falsely large
Too thin
If the medium is too thin the zones will be falsely _____
Large
