Antimicrobial Agents & AST

Question 1

Inhibits transport of lipid-bound precursors across the cytoplasmic membrane; from Bacillus licheniformis

Answer 1

Bacitracin (Taxo A)

Question 2

Act like detergents which interact with phospholipids, increasing permeability

Answer 2

Polymyxins

Question 3

Bacteria that possess OmpF and OmpC which decreases the permeability of B-lactams

Answer 3

E. coli

Question 4

Gene possessed by MRSA which encodes for PBP (B-lactamase-resistant transpeptidase) with a low affinity for B-lactams

Answer 4

mecA

Question 5

Gene possessed by S. agalactiae against macrolides

Answer 5

mreA

Question 6

Agar used for Kirby Bauer Disk Diffusion Method

Answer 6

Muller-Hinton Agar

Question 7

Aid for visualization between broth and McFarland standard

Answer 7

Wickerman card

Question 8

Automated inspection of turbidity

Answer 8

Nephelometer or spectrophotometer

Question 9

What does a large ZOI mean?

Answer 9

Effective antibiotic (susceptible)

Question 10

Standard disk width

Answer 10

6 mm

Question 11

Diameter of MHA used

Answer 11

150 mm

Question 12

How many disks can the plate accommodate?

Answer 12

12

Question 13

Distance between antibiotic disks to prevent overlapping

Answer 13

> 24 mm

Question 14

What are the temperature and time for incubation?

Answer 14

35C for 16-18 hours (5-10% for fastidious organisms)

Question 15

Broth used for broth dilution

Answer 15

Mueller-Hinton broth

Question 16

Testing 1 or 2 antibiotics with the use of 13 test tubes (1-2 mL)

Answer 16

Macrodilution

Question 17

What tube # will be the inoculum control in macrodilution?

Answer 17

Tube 11

Question 18

What tube # will be the antibiotic control in macrodilution?

Answer 18

Tube 13

Question 19

Standard inoculum for broth dilution

Answer 19

5x10^5 CFU/mL

Question 20

Standard inoculum for agar dilution

Answer 20

1x10^4 CFU/mL

Question 21

What is the lowest concentration of an antimicrobial agent in agar that completely inhibits visible growth?

Answer 21

Minimum inhibitory concentration (MIC)

Question 22

Standard inoculum for disk diffusion

Answer 22

1.5x10^8 CFU/mL

Question 23

What happens if the agar depth is <3mm?

Answer 23

False susceptibility

Question 24

What happens if the age of inoculum exceeds 24 hours?

Answer 24

False susceptibility

Question 25

Test for fastidious organisms where thin plastic strips (with gradations) containing antibiotics are placed in a radial fashion on an inoculated plate

Answer 25

Episolemeter test (E-test)

Question 26

What would be the MIC on CHROM agar if there is presence of MRSA?

Answer 26

> 4 ug/mL

Question 27

Measures the rate of killing pf bacteria by measuring the number of remaining viable bacteria

Answer 27

Time kill assay

Question 28

Measures susceptibility to a combination of antimicrobial agents

Answer 28

Synergy

Question 29

What antimicrobial level is the therapeutic indicator?

Answer 29

Peak level (15-20 minutes after dose is administered)