AST Flashcards
Products of microorganisms that reacts with and inhibit the growth of another microorganisms
Antibiotics
Performed on bacteria causing an individuals infection after they have been recovered in a culture of the specimen
Antibiotic susceptibility testing
What is the most common diffusion method?
Kirby-Bauer diffusion method
What is the population density?
1.5 x 10^8 CFU/mL
What is the recommended McFarland?
0.5 McFarland Standard
What is the component of McFarland?
Sulfuric acid and barium chloride
Enumerate the diffusion method
- kirby bauer diffusion method
- agarcup diffusion method
- agar cylinder diffusuon method
- epsilometer or gradient diffusion method
Enumerate the dilution method
- macrobroth method or tube dilution method
- microtube dilution method
What will you obtain if you mix barium chloride to sulfuric acid?
Barium sulfate
The zone of inhibition is measured in
Millimeter
Too thick medium will cause
Small zones
An inoculum as turbid as the 0.5 McFardland contains how many CFU/ml?
1.5x10^8
What is the recommended pH for AST?
7.2 pH (7.2-7.4)
What instrument is used when placing antibiotic discs on the media?
Forceps
What is the depth of the agar?
3 mm - 5 mm
What is the culture media of choice for disc diffusion AST?
Mueller Hinton Agar
What instrument is used to measure the zone of inhibition?
Microcaliper or ruler
The composition of a 10 no 0.5 McFarland standard is
99.5 ml of 1% sulfuric acid + 0.5 mL 1.175% of Barium chloride
Other term for kirby bauer method
Agar diffusion method or disk diffusion method
How long is the incubation for non-fastidious organisms?
16-20 hours
How long is the incubation for fastidious organisms?
20-24 hours
Enumerate the media that we can use in preparation of pure inoculum
- mueller hinton broth
- trypticase soy broth
- sterile distilled water
- natural saline solution
- brain heart infusion broth
If standard more turbid than inoculum…
Add colonies to inoculum
If inoculum more turbid than standard…
Add distulled water to inoculum
Heavy inoculum will result in
Small zone sizes
Lighter inoculum will result in
Larger zone sizes
Indicates that the organisms is inhibited by the recommended dose, at the infection site of an Antimicrobial agent
Susceptible or sensitive
Organisms is not inhibited by recommended dose
Resistant
Represents an organisms that may require a higher dose of antibiotic for a longer time period to be inhibited
Intermediate
Enumerate the step by step procedure for kirby bauer method
- preparation of pure inoculum using Mueller-Hinton broth
- standardize pure inoculum using 0.5 McFarland standard
- streak the pure inoculum into the media
- apply antibiotic discs
- incubate
- measure the diameter of zone of inhibition
- interpret the result
