Water Analysis

Question 1

What are antibiotics?

Answer 1

They are natural; antimicrobial agents produced by microorganisms.

Question 2

What is the general procedure of the experiment?

Answer 2

Plate is swabbed with organism to be tested, after it is dried antibiotic disks are added at least 15mm from edge of plate, and plates are incubated 16-18 hours at 37C

Question 3

if the organism is susceptible to it what will happen?

Answer 3

Zone of inhibition, a clearing surrounding the disk where the concentration is high enough to stop the growth

Question 4

Susceptibility Testing

Answer 4

Complete resistance = growth directly around the disk
.Susceptibility (or sensitivity) = bacteria cannot grow directly around the disk
.Area around the disk without bacterial growth = ZONE OF CLEARING or ZONE OF INHIBITION

Question 5

Sensitive

Answer 5

the bacteria begin to grow but ARE SENSITIVE or SUSCEPTIBLE to the antimicrobial drug
at a high concentration of the drug (i.e., close to the disk) the bacteria will be killed (no growth)
as the concentration of the drug decreases (i.e., further from the disk) there will be a point where the bacteria can survive the concentration of the drug and grow

Question 6

MINIMAL INHIBITORY CONCENTRATION (MIC)

Answer 6

moving away from the disk the antimicrobial drug concentration decreases
at a certain drug concentration the bacteria will be able to overcome the presence of the drug and grow
the periphery of the zone of clearing is the lowest drug concentration can kill or inhibit bacterial growth = MINIMAL INHIBITORY CONCENTRATION (MIC)

Question 7

What happens if the agar plate is too thick?

Answer 7

since the drug must diffuse down through a large amount of media before it can spread laterally the diameter of the concentration gradient will be small
narrow concentration gradient can result in a smaller zone of clearing and slows down lateral diffusion

Question 8

What happens if the agar plate is too thin?

Answer 8

ince drug has very little media to diffuse down into before it can spread laterally the diameter of the concentration gradient will be large
wide concentration gradient can result in large zone of clearing

Question 9

If bacterial concentration less than the approved McFarland standard then that means?

Answer 9

The drug more effective since there are fewer bacteria to act on = lower concentration of drug required to kill the bacteria = larger zone of clearing = incorrect interpretation of results

Question 10

If bacterial concentrations are higher than the approved McFarland standard then what does that mean?

Answer 10

The standard drug is not as effective since it must act on a much greater number of bacteria = a higher concentration of drug is required to kill the bacteria = smaller zone of clearing = incorrect interpretation of results

Question 11

You will measure the diameter of the zones in

Answer 11

millimeter and then convert it

Question 12

When treating an infected patient, we want to use the antibiotic that will both be the safest and most effective against the disease.

The widely used test for measuring the effectiveness of antibiotics is

Answer 12

Kirby-Bauer method

Question 13

Kirby-Bauer Test is routinely done to monitor

Answer 13

the prevalence of antibiotic-resistant bacteria

Question 14

Sensitive means

Answer 14

bacteria will be killed by the antibiotic

Question 15

Resistant means

Answer 15

ineffective to the antibiotic

Question 16

The Kirby- Bauer Antibiotic Sensitivity Test measures

Answer 16

the zone of inhibition

Question 17

what is the method to test for sensitivity that the Kirby- Bauer Antibiotic Sensitivity Test uses

Answer 17

disk diffusion method

Question 18

how deep must agar be

Answer 18

4mm deep

Question 19

temperature of incubation

Answer 19

35-37 degrees C

Question 20

Bacteria can be called what three things based on the zone of inhibition?

Answer 20

1) Sensitive
2) Resistant
3) Intermediate

Question 21

The larger the zone of inhibition, the _______ the bacterium is to the antibiotic.

Answer 21

Susceptible

Question 22

the smaller the zone of inhibition, the _______ the bacterium is to the antibiotic.

Answer 22

Resistant

Question 23

Give two examples of antibiotics used in the antimicrobial susceptibility test?

Answer 23

penicillin and tetracycline

Question 24

Why was E. coli and Staphylococcus aureus used in the antimicrobial susceptibility test?

Answer 24

they represent Gram - and + bacteria that are used to detect sensitive and resistant patterns