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Microbiology 484 > Susceptibility > Flashcards

Susceptibility Flashcards

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1
Q

B-lactam antibiotics

A

Penicillins
Cephalosporins
Carbapenems
Monobactams

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2
Q

B-lactam antibiotics mechanism of attack

A

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

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3
Q

Resistance to B-lactam

A

Caused by bacterial enzymes that destroy the antibiotic

Ex. altered targets (PBP), decreased intracellular uptake

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4
Q 
Streptomycin
Gentamicin
Neomycin
Kanamycin
Amikacin
Trobramycin
A

Aminoglycoside antibiotics

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5
Q

Aminoglycoside antibiotics mechanism of attack

A

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

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6
Q

1st, 2nd, 3rd gen cephalosporins

A

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

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7
Q

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

A

Alterations of positions R1 & R2

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8
Q

What effect does a bacteriostatic antibiotics have on the microbe?

A

Inhibits microbial growth, doesn’t kill it

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9
Q

What effect does a bactericidal antibiotic have on the microbe?

A

The antimicrobial agent actually kills the organism

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10
Q

CLSI recommendations for selective reporting for Group A

A

Antimicrobial agents that are done & reported routinely

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11
Q

CLSI recommendations for selective reporting for Group B

A

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

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12
Q

CLSI recommendations for selective reporting for Group C

A

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

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13
Q

CLSI recommendations for selective reporting for Group D

A

Urine antimicrobials

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14
Q

Quinoline group affect on microbes.

A

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

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15
Q

Members of quinoline group

A

Nalidixic acid, cinozacin, farehoxacin, ciproflaxacin

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16
Q

Cinoxacin, loracarbef, nitrofurantoin, sulfixoxazole, trimethoprim

A

Group D antibiotics

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17
Q

Ceftazidime, Kanamycin, netilmicin, tobramycin, tetracycline, chloramphenicol

A

Group C antibiotics

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18
Q

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

A

Group B antibiotics

19
Q

Group A antibiotics

A

Ampicillin, cefazolin, cephalothin, gentamicin

20
Q

Purpose of MBC

A

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

21
Q

Calculate MBC

A
  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

22
Q

Important criteria for Kirby-Bauer disk diffusion

A 
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
23
Q

Susceptible

A

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

24
Q

Resistant

A

Antimicrobial will most likely be ineffective

25
Q

Sensitive

A

Antimicrobial will most likely be effective at standard dose

26
Q

Intermediate

A

Antimicrobial is not likely be effective at standard dose

27
Q

E-test

A

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

28
Q

When the E-test is used

A

Anaerobes, fastidious orgs

29
Q

MRSA

A

Methicillin Resistant Staph aureus

30
Q

Treatment of MRSA

A

Vancomycin is the drug of choice

Patient isolation & control of microbe is critical

31
Q

VRE

A

Vancomycin resistant erythromycin

32
Q

VRE implications for patients

A

Control of nosocomial infections with patient isolation is imperative

33
Q

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

A

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

34
Q

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

A

Sulfonamides, trimethroprim, trimethoprim/sulfamethoxazole

35
Q

Klebsiella susceptibility pattern

A

Amp res

Ceph sens

36
Q

Enterobacter cloacae susceptibility pattern

A

Amp res

Ceph res

37
Q

E. coli susceptibility pattern

A

Amp variable

Ceph usually sens

38
Q

Pseudomonas aeruginosa susceptibility pattern

A

Aminoglycoside sens

39
Q

Staph aureus susceptibility pattern

A

Vancomycin sens

Oxacillin sens

40
Q

What are purity checks for Vitek & microscan systems?

A

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

41
Q

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

A

0.5 McFarland

42
Q

What is the CFU/mL of the dilution standard?

A

1.5 x 10 (8) CFU/mL

43
Q

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

A

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

Microbiology 484 (15 decks)

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