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Clinical Bacteriology > Antimicrobial Susceptibility Testing > Flashcards

Antimicrobial Susceptibility Testing Flashcards

1
Q

this is performed on bacteria and fungi isolated from clinical specimens to determine which anti-microbial agents might be effective in treating infections

A

antimicrobial susceptibility testing

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2
Q

T or F

only organisms that are likely to be contributing to an infection should be tested

A

true

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3
Q

testing organisms that are not involved in an infection may be misleading and could lead to a more serious infection with the development of?

A

antimicrobial resistance

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4
Q

one of the major purpose of clinical microbiology laboratory

A

identify organisms that cause infections

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5
Q

susceptibility testing on bacteria is often performed by what method?

A

disk diffusion or dilution method or minimal inhibitory concentration method (MIC)

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6
Q

standards that describe methods for susceptibility testing are published by this body

A

Clinical and Laboratory Standards Institute

formerly National Committee for Clinical Laboratory Standards

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7
Q

this is one of the most critical steps in susceptibility testing

A

inoculum preparation

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8
Q

false susceptible results occur if?

A

too few bacteria are tested

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9
Q

false resistant results occur if?

A

too many bacteria are tested

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10
Q

most widely used method of inoculum standardization involves comparing the turbidity of the inoculum preparation with?

A

McFarland turbidity standards

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11
Q

how to prepare McFarland standards?

A

adding specific volumes of 1% sulfuric acid and 1.175% barium chloride to obtain barium sulfate solution with a specific optical density

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12
Q

most commonly used McFarland standard

A

0.5 standard which contains 99.5 mL of 1% sulfuric acid and 0.5 mL of 1.175% barium chloride

stored in the dark at room temp

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13
Q

McFarland turbidity standard

bacterial inoculum size

A

1.5x10^8 colony forming units per mL

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14
Q

McFarland turbidity standard

standard medium

A

Mueller-Hinton Heated Agar

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15
Q

McFarland turbidity standard

standard depth

A

4-6mm

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16
Q

McFarland turbidity standard

standard pH

A

7.2-7.4

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17
Q

McFarland turbidity standard

atmosphere requirement

A

aerobic, no carbon dioxide

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18
Q

McFarland turbidity standard

temperature

A

35-37 degrees Celsius

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19
Q

once inoculum is standardized, inoculum suspension should be used within how many minutes?

A

15 minutes after preparation

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20
Q

a convenient and more precise alternative to visual adjustment to match McFarland standard is to use what instrument?

A

nephelometric or spectrophotometric device

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21
Q

McFarland turbidity standard

incubation time

A

18-24 hours

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22
Q

these methods are used to determine the MIC or the lowest concentration of antimicrobial agent required to inhibit the growth of the bacterium

A

dilution antimicrobial susceptibility test methods

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23
Q

final bacterial concentration

disk diffusion method

A

1.5x10^8 CFU/mL

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24
Q

final bacterial concentration

broth dilution

A

5x10^55 CFU/mL

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25
Q

final bacterial concentration

agar dilution

A

1x10^4 CFU/mL

26
Q

this method is when specific volumes of antimicrobial solutions are dispensed into premeasured volumes of molten and cooled agar which is subsequently pooured into standard petri dishes

A

agar dilution method

27
Q

recommended agar for testing aerobic isolates

A

Mueller-Hinton agar

28
Q

shelf life of agar dilution plates

A

1 week stored at 2 to 8 degrees Celsius

many drugs are labile

29
Q

it is generally performed in research settings

A

agar dilution method

30
Q

agar dilution method is currently considered the reference method for antimicrobial susceptibility testing of what microorganisms?

A

anaerobes and Neisseria gonorrhoeae

31
Q

it is commonly known as the Kirby-Bauer test and is the first standardized method described

A

disk diffusion test

32
Q

in this test, a McFarland 0.5 standardized suspension of bacteria in Mueller-Hinton broth is swabbed over the surface of a standardized Mueller-Hinton agar plate, and paper disks containing specific concentrations of antimicrobial agent are placed onto the inoculated surface

A

disk diffusion testing

33
Q

this is measured in the disk diffusion method

A

diameters of the zones produced by antimicrobial inhibition of bacterial growth

34
Q

reporting of results for disk diffusion testing

A
  • nonsusceptible
  • susceptible
  • intermediate
  • resistant
35
Q

disk diffusion test depends on the formation of this as the microbial agent radially diffuses into the agar

A

a gradient of antimicrobial concentrations

36
Q

T or F:

the drug concentration decreases at increasing distances from the disk

A

true

37
Q

this is related MICs and it is this relationship that has been used to determine breakpoints for interpretation of disk diffusion method

A

zone of inhibition

38
Q

composition of Mueller-Hinton agar

A
  • beef infusion solids
  • starch
  • casein
  • hydrolysate agar
39
Q

it is a test that measures the effectiveness with which penicillin in serum killed bacteria associated with endocarditis

A

serum bactericidal test

40
Q

it is analogous to the MIC-MBC test except that the medium used in patient’s serum

A

serum bactericidal test

41
Q

oxacillin agar screen is also known as:

A

oxacillin resistance screening agar

42
Q

it is a specialized medium used for the screening of oxacillin-resistant microorganisms

A

oxacillin agar screen

43
Q

oxacillin agar screen primarily focuses on detecting what?

A

MRSA

methylene resistant Staphylococcus aureus

44
Q

positive results of oxacillin agar screen

A

blue indicator - aniline blue

45
Q

negative result of oxacillin agar screen

A

white or pale color indicators

46
Q

it encodes the penicillin-binding protein, which has a low affinity for binding all beta lactam drugs

A

mec A gene

47
Q

this makes detecting oxacillin resistance difficult

A

heteroresistance or heteregoneous expression of resistance

48
Q

isolates of Staphylococcus aureus with reduced susceptibility to vancomycin

A

vancomycin-intermediate Staphylococcus aureus (VISA)

49
Q

this method is used to detect VRSA and enterococci resistant to VAN (vancomycin)

A

vancomycin agar screen

50
Q

what is the basal media used for vancomycin agar screen

A

brain heart infusion agar (BHIA)

51
Q

vancomycin agar screen

it is resistant to if:

A

there is more than one colony growth

developed mutations in the cell walls

52
Q

vancomycin agar screen

it is susceptible if:

plasmid containing vanA vancomycin resistance gene from vancomycin resistant enterococci

A

there is no growth

53
Q

it is used to detect inducible clindamycin resistance in bacteria, particularly in coagulasenegative staphylococci and S. aureus

A

d-test

54
Q

disks used for D-test

A

erythromycin and clindamycin disks

15-16cm distance

55
Q

synergy testing

counteractive effects result in much less activity than would be expected

A

antagonism

56
Q

synergy testing

the sum of the effects of the chemicals involved in the reaction is equal to the effect on the individual

A

indifference

57
Q

synergy testing

combined effect is greater than the additive effect

A

synergy

58
Q

it is a medthod used to study the antimicrobial activity of a compound over time

A

time kill assay

59
Q

time kill assay helps detemined what properties of an antimicrobial agent against a particular microorganism?

A

bactericidal or bacteriostatic

60
Q

it is a quantitative method used to determine the MIC of antimicrobial agents against specific microorganisms

A

E-test

61
Q

it is a drug used to treat infections caused by bacteria and other microorganism

A

antibiotics

62
Q

it is produced by microorganisms that it sends outside its cell to harm or kill another microorganism

A

antibiotics

Clinical Bacteriology (3 decks)

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