Susceptibility

Question 1

B-lactam antibiotics

Answer 1

Penicillins
Cephalosporins
Carbapenems
Monobactams

Question 2

B-lactam antibiotics mechanism of attack

Answer 2

B-lactam is 4 membered ring that takes the place of the normal structure in transpeptidase reaction, disrupting the formation of the cell wall

Question 3

Resistance to B-lactam

Answer 3

Caused by bacterial enzymes that destroy the antibiotic

Ex. altered targets (PBP), decreased intracellular uptake

Question 4

Streptomycin
Gentamicin
Neomycin
Kanamycin
Amikacin
Trobramycin

Answer 4

Aminoglycoside antibiotics

Question 5

Aminoglycoside antibiotics mechanism of attack

Answer 5

Binds specifically to 16S ribosomal unit @ the A binding site in the 30S ribosomal unit, prevents the docking of aminoacyl transfer RNA, causing it to be misread, leaving org unable to synthesize proteins vital to growth

Question 6

1st, 2nd, 3rd gen cephalosporins

Answer 6

B-lactam ring is 6-member dihydrothiazine ring, allowing more resistance to hydrolysis than 5-member ring
Basic structure has more modifiable sites to increase action against bacteria

Question 7

Differences in 1st, 2nd, 3rd gen cephalosporins

Answer 7

Alterations of positions R1 & R2

Question 8

What effect does a bacteriostatic antibiotics have on the microbe?

Answer 8

Inhibits microbial growth, doesn’t kill it

Question 9

What effect does a bactericidal antibiotic have on the microbe?

Answer 9

The antimicrobial agent actually kills the organism

Question 10

CLSI recommendations for selective reporting for Group A

Answer 10

Antimicrobial agents that are done & reported routinely

Question 11

CLSI recommendations for selective reporting for Group B

Answer 11

Reported only if an organism shows resistance to A agents/patients cannot tolerate A agents/infection is not responding/or it is a multi organism infection

Question 12

CLSI recommendations for selective reporting for Group C

Answer 12

Broad-spectrum activity, orgs resistant to A & B agents

Question 13

CLSI recommendations for selective reporting for Group D

Answer 13

Urine antimicrobials

Question 14

Quinoline group affect on microbes.

Answer 14

Inhibition of DNA gyrase by binding to the A subunit of DNA gyrase. Enzymes needed are topoisomerases I, II, III, IV
Specifically targets the topoisomerase I & II & prevents the supercoiling of DNA by inhibiting synthesis

Question 15

Members of quinoline group

Answer 15

Nalidixic acid, cinozacin, farehoxacin, ciproflaxacin

Question 16

Cinoxacin, loracarbef, nitrofurantoin, sulfixoxazole, trimethoprim

Answer 16

Group D antibiotics

Question 17

Ceftazidime, Kanamycin, netilmicin, tobramycin, tetracycline, chloramphenicol

Answer 17

Group C antibiotics

Question 18

Mezlocillin, ticarcillin, amoxicillin group, cephalosporins other than ceftazidime, amikacin, T/S

Answer 18

Group B antibiotics

Question 19

Group A antibiotics

Answer 19

Ampicillin, cefazolin, cephalothin, gentamicin

Question 20

Purpose of MBC

Answer 20

For immunosuppressed patients or very serious infections
The synergistic combination of the antimicrobial & patient’s own immune system is weak
To just inhibit the microbe may not sufficient & bactericidal levels are needed

Question 21

Calculate MBC

Answer 21

1. From growth well, dilute organism to 1:1000 (.01 mL in 10mL saline)
2. 0.01 mL aliquot is plated from a clear well
3. 18 hours - growth plate = # of colonies x 10^4

MBC end point is calculated if 99.9% killing has occurred

Question 22

Important criteria for Kirby-Bauer disk diffusion

Answer 22

Lawn correct conc. of microbe on media
Select appropriate disks
Press lightly on surface within 15 mins of inoculation
Incubate 16-18 hrs
NO CO2 unless required
Standardized depth of media

Question 23

Susceptible

Answer 23

A regression analysis plot is used by CLSI & US FDA to develop zone interpretation criteria

Question 24

Resistant

Answer 24

Antimicrobial will most likely be ineffective

Question 25

Sensitive

Answer 25

Antimicrobial will most likely be effective at standard dose

Question 26

Intermediate

Answer 26

Antimicrobial is not likely be effective at standard dose

Question 27

E-test

Answer 27

Standardized conc. of bacteria is lawned on media. A plastic test strip with antimicrobial (with conc. gradient) is on back is placed on inoculated media. An elliptical inhibitory area is formed around each strip. The MIC is determined where the growth ellipse intersects the E test strip

Question 28

When the E-test is used

Answer 28

Anaerobes, fastidious orgs

Question 29

MRSA

Answer 29

Methicillin Resistant Staph aureus

Question 30

Treatment of MRSA

Answer 30

Vancomycin is the drug of choice | Patient isolation & control of microbe is critical

Question 31

VRE

Answer 31

Vancomycin resistant erythromycin

Question 32

VRE implications for patients

Answer 32

Control of nosocomial infections with patient isolation is imperative

Question 33

Why are disk diffusion plates not incubated under increased carbon dioxide atmosphere?

Answer 33

Unless specifically recommended for a particular fastidious microbe, ambient atmosphere should be used because CO2 lowers the pH, which affects the activity of some antimicrobial agents

Question 34

Zone of 80% or more inhibition is considered susceptible with which antimicrobial agents?

Answer 34

Sulfonamides, trimethroprim, trimethoprim/sulfamethoxazole

Question 35

Klebsiella susceptibility pattern

Answer 35

Amp res | Ceph sens

Question 36

Enterobacter cloacae susceptibility pattern

Answer 36

Amp res | Ceph res

Question 37

E. coli susceptibility pattern

Answer 37

Amp variable | Ceph usually sens

Question 38

Pseudomonas aeruginosa susceptibility pattern

Answer 38

Aminoglycoside sens

Question 39

Staph aureus susceptibility pattern

Answer 39

Vancomycin sens | Oxacillin sens

Question 40

What are purity checks for Vitek & microscan systems?

Answer 40

Plate set up from dilution of microbe that was used in the automated system. A visual scan is done to verify that a single colony morphology alone was used & not a mix

Question 41

What is the turbidity standard for microbe dilution used in the Kirby-Bauer technique

Answer 41

0.5 McFarland

Question 42

What is the CFU/mL of the dilution standard?

Answer 42

1.5 x 10 (8) CFU/mL

Question 43

What is the CFU/mL of the dilution placed in automated systems?

Answer 43

5 x 10 (5) CFU/mL in each microtiter well