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MLS 223/L MIDTERMS > LAB S18 > Flashcards

LAB S18 Flashcards

1
Q

an in vitro measure to determine the susceptibility of microorganisms to one or several antimicrobial agents

A

Antimicrobial susceptibility testing (AST)

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2
Q

Data from the evaluation of microorganisms’ antibiogram are reported in the form of

A

minimum inhibitory concentration (MIC)

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3
Q

Latin for “within the glass”

A

In vitro

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4
Q

Latin for “within the living”

A

in vivo

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5
Q

compounds which act against microorganisms by blocking essential cellular processes

A

Antimicrobial agents

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6
Q

what cellular processes are blocked by antimicrobial agents

A
  • cell wall synthesis
  • protein synthesis
  • DNA replication/transcription
  • cellular respiration
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7
Q

antimicrobial agents that inhibit microbial growth are called

A

microbistatic

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8
Q

antimicrobial agents that kill microorganisms are called

A

microbicidal

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9
Q

the susceptibility profile of a microorganism

A

antibiogram

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10
Q

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

A

Minimum Inhibitory Concentration

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11
Q

Antimicrobial susceptibility tests are widely used for bacterial infections but are less frequently used for fungal, viral, and parasitic infections. T or F

A

True

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12
Q

uses of antimicrobial susceptibility testing

A
  • As a chemotherapeutic guide
  • As an epidemiological surveillance tool
  • As a laboratory diagnostic tool
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13
Q

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

A

antimicrobial drugs

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14
Q

antimicrobial drugs often act within the host and subsequently damage the host, which is an important principle of selective toxicity. T or F

A

False. They often act within the host without damaging the host, which is an important principle of selective toxicity.

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15
Q

This result implies that therapy with the recommended dosage of a particular antibiotic is likely to be effective in eradicating the infection

A

susceptible

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16
Q

indicates that the antibiotic in the appropriate dose has not
been shown to have a high likelihood of treatment success in clinical trials

A

resistant

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17
Q

AST plays an essential role in guiding the clinician in the prescription of
antibiotics for treatment of an infection

A

AST as a chemotherapeutic guide

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18
Q

If the susceptibility profile is predictable, it is still necessary to do testing on an isolate. T or F

A

False. if the susceptibility profile is predictable, it is not necessary, in most
cases, to do testing on an isolate.

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19
Q

When is it not necessary to do a testing on an isolate

A

– Streptococcus pyogenes is usually susceptible to penicillin
– Anaerobes are susceptible to metronidazole
– Klebsiella pneumoniae is generally ampicillin-resistant
– Proteus species are generally resistant to nitrofurantoin and
tetracyclines.

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20
Q

Testing should be limited to those isolates that are definite pathogens, why?

A

testing of isolates that are “contaminants” or “normal flora” is
expensive and time-consuming and may lead to unnecessary
administration of antibiotics

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21
Q

predicts the effectiveness of the antibiotic being tested against a particular bacterial species or strain.

A

Antimicrobial Susceptibility Testing

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22
Q

AST is intended to be a guarantee that a particular agent or drug combination will be effective in therapy. T or F

A

False. AST is intended to be a guide for the

clinician, not a guarantee that a particular agent or drug combination will be effective in therapy.

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23
Q

In vitro susceptibility is a prerequisite for the _______ of an
antibiotic

A

in vivo efficacy

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24
Q

advantages of epidemiological surveillance tool

A
  • aid to monitor susceptibility patterns of bacterial isolates
  • aid in initiating appropriate empiric antibiotic therapy
  • used to monitor emergence of acquired resistance.
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25
Q

bacterial pathogens of Community-acquired pneumonia (CAP)

A
  • streptococcus pneumoniae
  • haemophilus influenzae
  • chlamydophila pneumoniae
  • mycoplasma pneumoniae
  • moraxella catarrhalis

Senior High Cool MM

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26
Q

Penicillin remains the standard drug of choice in the treatment of
low-risk CAP in patients without comorbid illness.

A

False. amoxicillin remains the standard drug of choice in the treatment of
low-risk CAP in patients without comorbid illness.

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27
Q

more than 10-20% of isolates of group A streptococcus (S. pyogenes) are
susceptible to bacitracin. T or F

A

False. more than 99% of isolates of group A streptococcus (S. pyogenes) are susceptible to bacitracin

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28
Q

a very small percentage of isolates of group B streptococcus and 10% to 20% of isolates of groups C and G streptococcus are also susceptible. T or F

A

True

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29
Q

Agar disk diffusion susceptibility tests became standardized in the United States based on the work of

A

Kirby, Bauer and coworkers

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30
Q

Principle of agar disk diffusion susceptibility

A

Agar disk diffusion method relies on the diffusion of antimicrobial agent released from an impregnated paper disk through the agar. As soon as the antimicrobial agent-impregnated disk comes in contact with the moist agar surface, water is absorbed into the filter paper and the antimicrobial agent
diffuses into the surrounding medium.

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31
Q

used routinely for testing common, rapidly growing, and certain fastidious bacterial pathogens because of its ease of use and lower cost compared to other methods.

A

agar disk diffusion method

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32
Q

random molecular motion

A

diffusion. high concentration to low concentration

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33
Q

important note

A

The rate of extraction of the antimicrobial agent out of the disk is
greater than its outward diffusion into the medium, so
that the concentration immediately adjacent to the
disk may exceed that in the disk itself.

As the distance from the disk increases, however, there is a logarithmic
reduction in the antimicrobial agent concentration.

34
Q

When a critical cell mass of bacteria is reached, the inhibitory
activity of the antimicrobial agent is overcome and
bacterial growth occurs. T or F

A

True

35
Q

The points at which the critical cell mass is reached appear as

A

a sharp circle with a margin of bacterial growth, with the middle of
the disk forming the center of the circle

36
Q

The concentration of diffused antimicrobial agent at this interface of growing and inhibited bacteria is known as

A

critical concentration

-approximates the minimum inhibitory concentration (MIC) obtained in dilution tests

37
Q

The sizes of zones of growth inhibition vary with the pharmacologic characteristics of different antimicrobial agent.

A

True

38
Q

the zone size of one agent cannot be compared to the zone size of
another agent acting on the same organism. However, for any one agent, the zone size can be compared to a standard, provided that all conditions are controlled.

A

True

39
Q

Standards for the practice of microbiology are published by

A

Clinical and Laboratory Standards Institute (CLSI)

40
Q

covers the standards for agar disk diffusion method used to determine the in vitro antimicrobial susceptibility of bacteria that grow aerobically, and can be modified to test certain fastidious bacterial pathogens.

A

CLSI document M02

41
Q

It describes how to perform the agar disk

diffusion and the criteria for quality control testing

A

CLSI document M02

42
Q

presents tables that represent the most current information for drug selection, interpretation, and quality control using the procedures standardized in M02, M07, and M11

A

presents CLSI document M100

43
Q

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

A

M07

44
Q

Standards for antimicrobial susceptibility of bacteria that grow anaerobically.

A

M11

45
Q

Interpretative categories of the Agar Disk Diffusion Susceptibility Test

A
  • Susceptible
  • Resistant
  • Intermediate
  • Susceptible dose dependent (SDD)
  • Nonsusceptible
46
Q

Implies that the isolates are inhibited by the usually
achievable concentrations of antimicrobial agent when the
dosage recommended to treat the site of infection is used
resulting in likely clinical efficacy

A

Susceptible (S)
-A category defined by zone diameters at or above (or MIC at
or below) the susceptible breakpoint

47
Q

Implies that isolates are not inhibited by the usually
achievable concentrations of the agent with normal dosage
schedules, or specific microbial resistance mechanisms are
likely and clinical efficacy of the agent against the isolate has
not been reliably shown in treatment studies.

A

Resistant (R)
-A category defined by zone diameters at or below (or MICs
at or above) the resistant breakpoint

48
Q

Implies clinical efficacy in body sites where the drugs are
physiologically concentrated or when a higher than normal
dosage of the drug can be used. This category also includes
a buffer zone which should prevent small, uncontrolled,
technical factors from causing major discrepancies in
interpretations especially for drugs with narrow
pharmacotoxicity margins

A

Intermediate (I)
-A category defined by zone diameters (or MICs) within the
intermediate range that approach usually attainable blood
and tissue levels and for which response rates may be lower
than for susceptible isolates

49
Q

A category defined by a breakpoint that implies that
susceptibility of an isolate is dependent on the dosage
regimen that is used in the patient

A

Susceptible dose dependent (SDD)

50
Q

This should not be used when describing organism/drug
category with intermediate or resistant interpretive
categories.

A

Nonsusceptible (NS)

51
Q 
Isolates for which the zone 
diameters below (or MICs above) the value indicated for the 
susceptible breakpoint should be reported as
A

nonsusceptible

52
Q

Variables of AST

A
  • Inoculum
  • test medium
  • antimicrobial disks
  • incubation
  • reading and interpretation of results
53
Q

Variables of the test found in the inoculum

A
  • Purity
  • Age
  • Density
54
Q

How to counter variabilities in the PURITY of inoculum

A
  • pure culture should be sampled to minimize variation in the bacterial population
  • select well-isolated colonies of the same morphological type
  • get 3-5 same-looking colonies to minimize the possibility of testing susceptible colonies only and missing the resistant mutants
55
Q

How to counter variabilities in the AGE of inoculum

A

-Bacteria to be tested must be in the logarithmic phase of
growth
-Broth culture method of inoculum preparation
-Colony suspension method of inoculum preparation

56
Q

The inoculum is prepared from broth culture (usually

Trypticase Soy Broth, TSB) that has been incubated for 2-6 hours

A

Broth culture method of inoculum preparation

57
Q

It is used for nonfastidious organisms (except
staphylococci) when fresh (18-24 hour) colonies are
not available

A

Broth culture method of inoculum preparation

58
Q

formerly called growth method

A

Broth culture method of inoculum preparation

58
Q

formerly called growth method

A

Broth culture method of inoculum preparation

59
Q

formerly called direct colony suspension method

A

Colony suspension method of inoculum preparation

60
Q

The inoculum is made by directly suspending 18- to 24-hour-old colonies from nonselective media (such as blood agar) in broth or saline

A

Colony suspension method of inoculum preparation

61
Q

is used with most organisms if the time does not permit

incubation for 2 to 6 hours.

A

Colony suspension method of inoculum preparation

62
Q

It is recommended for testing the fastidious organisms:

  • Haemophilus influenzae
  • Haemophilus parainfluenzae
  • Neisseria gonorrhoeae
  • Neisseria meningitidis
  • streptococci
  • for testing staphylococci to detect methicillin
    (oxacillin) resistance.
A

Colony suspension method of inoculum preparation

63
Q

Aging and autolysing bacteria may not produce confluent
lawn of bacterial growth on AST plate, for they tend to be more
susceptible

A

True

64
Q

How to counter variabilities in DENSITY of the inoculum

A

-The TSB culture must contain a concentration of bacteria that
approximates the 0.5 McFarland turbidity standard,
approximately 1-2 x 108 colony-forming units
(CFUs) per milliliter

65
Q

A lower inoculum concentration (too light)

may lead to

A

larger zone of inhibition;

66
Q

higher inoculum concentrations (too dense) may lead to

A

smaller zone of inhibition

67
Q

Use the inoculum suspension within 10 minutes

after adjusting the turbidity.

A

False. Use the inoculum suspension within 15 minutes

after adjusting the turbidity.

68
Q

Variables in the Test Medium

A
  • Type
  • pH
  • Depth
  • Moisture
69
Q

is considered the best medium for

the routine AST of non-fastidious bacteria

A

Mueller-Hinton Agar (MHA)

70
Q

Why is Mueller-Hinton Agar (MHA) considered the best medium for
the routine AST of non-fastidious bacteria

A

-it shows acceptable batch-to-batch reproducibility for
AST.
- it is low in inhibitors that affect sulfonamides,
trimethoprim, and tetracycline susceptibility test results.
- it supports satisfactory growth of most non-fastidious
pathogens.
- a substantial amount of data and experience has been
collected about AST performed with this medium.

71
Q

MHA has very low concentrations of divalent cations but is
adjusted (cation-adjusted MHA, CAMHA) to physiologic
concentrations ____________
during production

A

(20 to 35 mg/L Mg2+ and 50 to 100 mg/L Ca2+)

72
Q

Mg2+ and Ca2+ affects

A

results of aminoglycoside and tetracycline tests with

Pseudomonas aeruginosa.

73
Q

Excess cation content

A

reduces zone sizes,

74
Q

low cation content may result in

A

unacceptably

large zone of inhibition

75
Q

if there are variations in divalent cations, ________ must be used

A

MHA that is low in thymidine or thymine content (< 50 ug/ml)

76
Q

Excessive amounts of thymidine or thymine can

A

reverse the
inhibitory effect of sulfonamides and trimethoprim thus yielding
smaller and less distinct zones or no zone at all. Enterococci are
particularly affected.

77
Q

The MHA should have a pH between ______ at room

temperature.

A

7.2 and 7.4

78
Q

If the pH <7.2

A 
Erythromycin = smaller zone of inhibition
Tetracyclines = larger zone of inhibition
79
Q

check the pH of Test Medium by

A

-macerating enough agar to submerge the tip of a pH
electrode
- allowing a portion of agar to solidify around the tip of
a pH electrode in a beaker or cup
- using a properly calibrated surface electrode.

MLS 223/L MIDTERMS (5 decks)

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