ANTIBIOTIC SUSCEPTIBILITY TESTING

Question 1

pH

Answer 1

7.2-7.4

Question 2

<7.2 pH:

Answer 2

FALSE RESISTANCE
🌼 Lose potency → Aminoglycosides, quinolones, macrolides
🌼 Excessive activity → Tetracycline

Question 3

> 7.4

Answer 3

FALSE SUSCEPTIBLE

Question 4

Density of Inoculum

Answer 4

0.5 MacFarland or 1.5 x 10^8 CFU/mL

Question 5

Inoculum too heavy

Answer 5

smaller zone / False Resistant

Question 6

Commonly used amount of inoculum

Answer 6

1% Sulfuric acid and 1.175% Barium Chloride

Question 7

Inoculum too light

Answer 7

lager zone / False Sensitive

Question 8

Thickness of the agar
Depth:

Answer 8

4-6mm

Question 9

Too thick (Deep):

Answer 9

Smaller zone size = False Resistant

Question 10

Antimicrobial agent diffuses down through the agar as well as outward.

Answer 10

Too thick (Deep) agar

Question 11

Too thin (Shallow):

Answer 11

Larger zone size = False Susceptible

Question 12

Usually read after

Answer 12

16-18 hours

Question 13

Read after 24 hours if:

Answer 13

✔Staphylococcus against oxacillin or vancomycin
✔ Enterococcus against Vancomycin

Question 14

Prolong incubation

Answer 14

smaller zone / False Resistance

Question 15

Shortened incubation

Answer 15

larger zone / False Susceptible

Question 16

Too moist =

Answer 16

Smaller Zone / False Resistance

Question 17

Too dry =

Answer 17

Larger Zone / False Susceptible

Question 18

Standard susceptibility medium for non-fastidious bacteria.

Answer 18

Mueller-Hinton Agar (МНА)

Question 19

Recommended medium for susceptibility testing because it has reduced concentration of inhibitors.

Answer 19

Mueller-Hinton Agar (МНА)

Question 20

concentration of an antimicrobial agent that coincides w/ a susceptible or intermediate MIC breakpoint for a particular drug.

Answer 20

Breakpoint
(cutoff)

Question 21

lowest concentration of the antimicrobial agent that is needed to kill the bacterial growth.

Answer 21

Minimum bactericidal concentration (MBC)

Question 22

lowest concentration of the antimicrobial agent that inhibits the bacterial growth.

Answer 22

Minimum inhibitory concentration (MIC)

Question 23

lowest concentration of antimicrobial agent that kills the bacterial growth when subculture in a fresh medium.

Answer 23

Minimum lethal concentration (MLC)

Question 24

decreased bactericidal activity at a higher drug concentration.

Answer 24

Paradoxic (eagle) effect

Question 25

involves growth at higher concentrations and no growth at 1 or more of the lower concentrations (contamination, improper incubation, improper concentration of antimicrobials & presence of unusual resistant isolate).

Answer 25

Skipped wells

Question 26

the ability of an organism to be inhibited by a drug which is normally bactericidal.

Answer 26

Tolerance

Question 27

involves heavy bacterial growth at lower concentrations that is followed by one or more wells that show greatly reduced growth in the form of a small button or a light haze

Answer 27

Trailing growth