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MICRO – BACTERIOLOGY- MYCOLOGY-VIROLOGY > ANTIBIOTIC SUSCEPTIBILITY TESTING > Flashcards

ANTIBIOTIC SUSCEPTIBILITY TESTING Flashcards

1
Q

What is the purpose of dilution in microbiology, and what numerical values do MIC, MBC, and MLC represent?

A

• Dilution in microbiology is used to quantitatively determine the Minimum Inhibitory Concentration (MIC), Minimum Bactericidal Concentration (MBC), and Minimum Lethal Concentration (MLC), with MIC, MBC, and MLC
• Representing numerical values as a result

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2
Q

What is the reporting format for disk diffusion testing using the Kirby Bauer method for antibiotic susceptibility?

A

• The results are reported qualitatively as either “Sensitive,” “Intermediate,” or “Resistant.”

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3
Q

What does MIC stand for, and what does it represent in microbiology?

A

• Minimum Inhibitory Concentration
• It represents the lowest concentration of a substance that inhibits bacterial growth.

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4
Q

What does MBC/MLC stand for in the context of antibiotic effectiveness?

A

• Minimum Bactericidal Concentration or Minimum Lethal Concentration
• Indicating the lowest concentration of antibiotic that can kill bacteria.

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5
Q

What factors can lead to a “LARGER ZONE - FALSE SENSITIVE” result in Kirby Bauer disk diffusion testing?

A
  • too thin agar
    *a very dry agar surface,
  • a too light inoculum
  • Thin medium
  • Delay before incubation
  • Low temperature and old colonies
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6
Q

What are some factors that can lead to a FALSE RESISTANT result in a SMALLER ZONE when conducting microbiological testing?

A
  • Too thick,
    excessive moisture on the agar surface,
    a heavy inoculum
    extended incubation time,
    and delay before disc application.
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7
Q

What are the two categories of antimicrobial agents based on their spectrum of activity?

A

• Can be categorized as broad spectrum or narrow based on their spectrum of activity.

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8
Q

What is the maximum number of antibiotic disks allowed on a 150 mm plate when swarming on Kirby Bauer?

A

• The maximum number allowed is 12 antibiotic disks.

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9
Q

What is the maximum number of antibiotic disks allowed on a 100 mm plate when swarming on Kirby Bauer?

A

• No more than 5 mm of disks

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10
Q

What is the recommended storage temperature for antibiotic disks in a working supply?

A

• The recommended storage temperature is 2-8°C.

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11
Q

Where should antibiotic disks in the working supply be placed for storage?

A

• They should be placed in the refrigerator (REF) for storage.

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12
Q

Name two classes of cell wall inhibitors in the context of antibiotic medications.

A

• beta lactams (including Penicillin, Cephalosporins, and Carbapenems)
• glycopeptide (Vancomycin).

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13
Q

Which antibiotics are classified as protein synthesis inhibitors?

A

• Aminoglycosides: Gentamycin Tetracycline
• MLS (macrolide lincosamide streptogramin) -erythromycin, Clarithromycin

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14
Q

What type of media is commonly used for the AST (Antibiotic Susceptibility Testing) of Streptococci, and why is it used?

A

• Typically performed using MHA (Mueller-Hinton Agar) supplemented with blood.
• This medium is used because Streptococci are fastidious organisms

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15
Q

What does “Broad Spectrum” mean in relation to antibiotics?

A

• “Broad Spectrum” antibiotics can act against many different types of bacteria.

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16
Q

What is the primary characteristic of “Bacteriostatic” antibiotics?

A

• “Bacteriostatic” antibiotics have an inhibitory effect on bacteria.

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17
Q

What is a limitation of “Narrow Spectrum” antibiotics?

A

• Limited range of action and typically target only gram-positive bacteria.

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18
Q

What is the defining feature of “Bactericidal” antibiotics?

A

• “Bactericidal” antibiotics have a killing effect on bacteria.

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19
Q

What is the Kirby Bauer Technique used for?

A

• The Kirby Bauer Technique is used for antimicrobial susceptibility testing.

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20
Q

What type of method is used in Kirby Bauer technique?

A

• The disk diffusion method is used in the Kirby Bauer Technique.

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21
Q

What media is prepared for this technique, and how is it applied in Kirby Bauer Technique?

A

• Media prepared is Mueller-Hinton Agar (MHA),
• Applied using a sterile cotton swab with overlapping streaking.

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22
Q

What should be the depth of the agar in this Kirby Bauer technique?

A

• The depth of agar should be 3-5mm.

23
Q

In Kirby Bauer Technique, What is the size of the antibiotic disks used?

A

• The antibiotic disks used are 6mm in size.

24
Q

In Kirby Bauer Technique, What is the recommended distance of the antibiotic disk from the center of the agar plate?

A

• The recommended distance of the disk from the center is 24mm.

25
Q

What is the distance between two antibiotic disks on the same plate in Kirby Bauer Technique?

A

• The distance between two antibiotic disks on the same plate is 15mm.

26
Q

In the Kirby Bauer Technique, What are the incubation conditions for the agar plates?

A

• Incubate the plates at 37°C for 16-18 hours.

27
Q

How should the zone of inhibition be measured, and what’s the rule regarding numerical values in the context of Kirby Bauer technique?

A

• The zone of inhibition should be measured using a ruler or caliper.

28
Q

What is the maximum number of plates allowed in the Kirby Bauer technique?

A

• The maximum number of plates allowed is 5.

29
Q

How many antibiotics should be on each disk in the Kirby Bauer technique?

A

• Each disk should contain only 1 antibiotic.

30
Q

Are numerical values allowed in the Kirby Bauer technique?

A

• No, numerical values are not allowed in this technique.

31
Q

What does a zone size of 16 mm indicate in the context of Kirby Bauer technique?

A

• A zone size of 16 mm suggests an intermediate level of sensitivity or resistance.

32
Q

In Kirby Bauer technique, If the zone size for inhibition is greater than 16 mm, what does it indicate?

A

• If the zone size is greater than 16 mm, it indicates sensitivity.

33
Q

In the context of Kirby Bauer technique, What does a zone size less than 16 mm imply?

A

• A zone size less than 16 mm implies resistance to the substance being tested.

34
Q

What is the primary purpose of antibiotic susceptibility testing?

A
  • The primary purpose of antibiotic susceptibility testing is to detect the ability of antimicrobial agents to inhibit bacterial growth in vitro.
35
Q

What does antibiotic susceptibility testing help determine?

A
  • Helps determine the susceptibility or resistance of organisms against antimicrobial agents.
36
Q

What is the Tube or Broth Dilution Method used for?

A
  • Used for challenging the organism of interest with microbial agents in a broth environment
  • To determine MIC and MLC concentrations.
37
Q

How is the concentration of antibiotic prepared in the Tube or Broth Dilution Method?

A
  • A specific amount of antibiotic is prepared in a decreasing concentration
  • In the broth by using the serial dilution technique
38
Q

What is the standard inoculum size used in this method?

A
  • The standard inoculum size for the Tube or Broth Dilution Method is 5 x 10^5 CFU/mL.
39
Q

What is the basic principle of the agar dilution method?

A
  • Combining antimicrobial concentrations and test organisms on an agar-based medium.
40
Q

What is the typical shelf life of an agar dilution plate for most antimicrobial agents?

A
  • The shelf life of an agar dilution plate is usually only 1 week for most antimicrobial agents.
41
Q

What is the agar medium used for testing anaerobes and Neisseria gonorrhoeae?

A
  • For anaerobes, the agar medium used is Brucella agar with leaked blood and Vitamin K.
42
Q

What is the standard inoculum size for the agar dilution method?

A
  • The standard inoculum size for the agar dilution method is 1 x 10^4 CFU/mL.
43
Q

What does MIC stand for, and what does it represent in a laboratory setting?

A
  • MIC stands for Minimal Inhibitory Concentration
  • It represents the lowest concentration of a substance that inhibits visible growth in vitro (in a laboratory environment).
44
Q

What does MBC stand for in the context of antibiotic effectiveness?

A
  • MBC stands for Minimal Bactericidal Concentration
  • Which represents the lowest concentration of the antibiotic required to kill a bacterium.
45
Q

What is the principle behind Disk Diffusion – Kirby Bauer (Qualitative) testing?

A
  • Based on the inverse linear relationship between the diameter of the zone of inhibited growth around the antibiotic disk
  • And the logarithm of the MIC (Minimum Inhibitory Concentration) of the antibiotic.
46
Q

Which types of microorganisms is Disk Diffusion testing limited to?

A
  • Disk Diffusion testing is limited to Aerobes and Facultative anaerobes
47
Q

What is the procedure in Disk Diffusion testing?

A
  • Filter paper disks impregnated with various antimicrobial agents of specific concentrations are carefully placed on an agar plate
  • Previously inoculated with the bacteria being tested.
48
Q

What is the primary purpose of Disk Diffusion testing?

A
  • To determine the susceptibility or resistance of a pathogenic organism to various antimicrobial agents.
49
Q

What is the purpose of using Muller Hinton Agar (MHA) in disk diffusion testing?

A
  • MHA is used as the susceptibility standard medium
50
Q

What is the standard inoculum size for the Kirby Bauer disk diffusion test?

A
  • The standard inoculum size for the Kirby Bauer test is 1.5 x 10^8 colony-forming units per milliliter (CFU/mL).
51
Q

How is the 0.5 MacFarland standard prepared for the disk diffusion test?

A
  • The 0.5 MacFarland standard is prepared by mixing 99.5 mL of 1% H2SO4 (sulfuric acid)
  • With 0.5 mL of 1.175% BaCl (barium chloride)
52
Q

How does an acidic pH affect Tetracycline, Novobiocin, and Methiliccin?

A
  • An acidic pH can decrease the effectiveness of Tetracycline, Novobiocin, and Methiliccin.
53
Q

How does an alkaline pH affect the activity of Aminoglycosides, Clindamycin, and Erythromycin?

A
  • Can reduce the effectiveness of Aminoglycosides, Clindamycin, and Erythromycin,
  • Potentially leading to decreased antimicrobial activity.
54
Q

What is the recommended storage temperature for antibiotic disks (working supply)?

A
  • The recommended storage temperature for antibiotic disks (working supply) is 2-8°C.

MICRO – BACTERIOLOGY- MYCOLOGY-VIROLOGY (12 decks)

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