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Clinical Bacteriology > LAB S18 > Flashcards

LAB S18 Flashcards

1
Q

determine the susceptibility of microorganisms to one or several antimicrobial agents

A

Antimicrobial Susceptability Test

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2
Q

act against microorganisms by blocking essential cellular processes

A

antimicrobial agents

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3
Q

Antimicrobial agents block essential cellular processes which are: (4)

A

> cell wall synthesis
protein synthesis
DNA replication/ transcription
cellular respiration

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4
Q

the property of being able to inhibit microbial growth

A

microbiostatic

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5
Q

the property of being able to kill microbes

A

microbicidal

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6
Q

pharmaceutical agents that include antibiotics (antibacterials), antifungal, antiviral , and antiparasitic drugs

A

antimicrobial drugs

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7
Q

susceptibility profile of a microorganism

A

antibiogram

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8
Q

lowest concentration of an antibiotic that inhibits visible growth of a microorganism in an in vitro system

A

Minimum Inhibitory Concentration (MIC)

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9
Q

Three major uses of AST

A
  1. As a chemotherapeutic guide
  2. As an epidemiological surveillance tool
  3. As a laboratory diagnostic tool
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10
Q

AST is used when susceptibility of bacteria cannot be predicted from its identity. However, it is not needed if the susceptibility profile is predicatable.

Streptococcus pyogenes is predictably susceptible to:

A

penicillin

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11
Q

Anaerobes are predictably susceptible to:

A

metronidazole

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12
Q

Klebsiella pneumoniae is predictably resistant to:

A

ampicillin

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13
Q

Proteus species is predictably resistant to:

A

nitrofurantonin and tetracyclines

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14
Q

Susceptibility:

Streptococcus pyogenes

A

penicillin

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15
Q

Suscpetibility:

Anaerobes

A

metronidazole

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16
Q

Resistance:

Klebsiella pneumonae

A

ampicillin

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17
Q

Resistance:

Proteus species

A

nitrofurantoin and tetracyclines

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18
Q

property of antimicrobial drugs wherein it acts within the host without damaging the host

A

selective toxicity

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19
Q

Three purposes of AST as an epidemiological surveillance tool

A

Aid in

  1. monitoring susceptibility patterns in a region or hospital
  2. appropriate empiric antibiotic therapy (giving amoxicillin for community acquired pneumonia)
  3. monitoring emergence of acquired resistance
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20
Q

Five most common bacterial pathogens for communith-acquired pneumonia (CAP)

A
  1. Streptococcus pneumoniae
  2. Haemophilus influenzae
  3. Chlamydophila pneumoniae
  4. Mycoplasma pneumoniae
  5. Moraxella catarrahlis
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21
Q

Most community acquired pneumonia bacterial pathogens are susceptible to:

A

amoxicillin

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22
Q

Streptococcus bacteria can be identified in laboratpry diagnosis through its susceptibility to:

A

Bacitracin

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23
Q

Bacitracin inhibits what groups of Streptococcus bacteria:

A

99% group A (S. pyogenes)
small percentage of group B
10-20% of group C and G

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24
Q

used routinely for testing common, rapidly growing, and certain fastidious bacterial pathogens

A

Kirby-Bauer Agar Disk Diffusion method

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25
Q

Principle of Kirby Bauer Agar Disk Diffusion Method

A

Diffusion

movement of molecules from area of high to low concentration

26
Q

Mode of Action of Kirby Bauer Agard Disk Diffusion Method

A

a. Impregnated disk of antimicrobial agent comes in contact with the moist agar surface
b. water is absorbed into the filter paper
c. antimicrobial agents diffuse into the surrounding medium

27
Q

The concentration of diffused antimicrobial agent at the interface of growing and inhibited bacteria, approximates the MIC

A

Critical Concentration

28
Q

Standards for agar disk diffusion method used to determine the in vitro antimicrobial susceptibility of bacteria that grow aerobically and can be modified for fastidious bacteria

29
Q

Standards for antimicrobial susceptibility of bacteria that grow aerobically using dilution methods

30
Q

Standards for antimicrobial susceptibility of bacteria that grow anaerobically

31
Q

contains tables that represent the most current information for drug selection, interpretation, and quality control

32
Q

Broth used in Kirby Bauer Inoculum

A

Trypticase Soy Broth (TSB)

33
Q

Turbidity of onoculum is compared ro

A

0.5 Mcfarland Standard

34
Q

Agar used in Kirby Bauer method

A

Mueller- Hinton Agar

35
Q

Inoculum variables that affect the test

A
  1. purity
  2. age (should be in log phase)
  3. density (0.5 Mcfarland Standard)
36
Q

Two types of Inoculum preparation

A
  1. Broth culture method (TSB incubated 2-6 hours)

2. Colony suspension method (direct suspension of 18-24 hrs old colony)

37
Q

Inoculum preparation method used for non fastidious bacteria (except staphyllococci)

A

broth culture method

38
Q

Inoculum preperation method used for fastidious bacteria

A

Colony suspension method

39
Q

Effect on ZOI:

Lighter turbidity of inoculum

A

larger ZOI

40
Q

Effect on ZOI:

Denser or more turbid inoculum

A

smaller ZOI

41
Q

4 test medium variables that affect the test:

A
  1. Type (should be MHA)
  2. pH
  3. Depth
  4. Moisture
42
Q

Most recommended Test medium type

A

Mueller- Hinton Agar (MHA)

43
Q

Physiologic concentration of divalent magnesium

A

20-35 mg/L

44
Q

physiologic concentration of divalent calcium

A

50-100 mg/L

45
Q

CFU/ml of Mcfarland compared inoculum

A

1-2 × 10^8

46
Q

Effect on ZOI:

less cation

A

larger ZOI

47
Q

Effect on ZOI:

more cation in test medium

A

smaller ZOI

48
Q

Effect on ZOI:

high thymidine

A

smaller ZOI

49
Q

recommended pH of test medium

A

7.2 to 7.4

50
Q

Effect on ZOI:

low pH of test medium on aminoglycosides and macrolides like erythromycin

A

smaller ZOI

51
Q

Effect on ZOI:

low pH of test medium for tetracyclines

A

larger ZOI

52
Q

Effect on ZOI:

high pH of test medium for aminoglycosides and macrolides like erythromycin

53
Q

Effect on ZOI:

high pH of test medium of tetracyclines

A

smaller ZOI

54
Q

recommended depth of test medium

55
Q

recommended mL for 100 mm plate

56
Q

recommended mL for 150 mm plate

57
Q

Effect on ZOI:

too shallow test medium

A

larger ZOI

58
Q

Effect on ZOI:

too deep test medium

A

smaller ZOI

59
Q

effect on ZOI

too dry test medium

A

smaller ZOI

60
Q

effect on ZOI

too moist test medium

A

larger ZOI

61
Q

diameter of antimicrobial disk

Clinical Bacteriology (12 decks)

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