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Microbiology > Lecture 21: MALDI-TOF and Sensitire > Flashcards

Lecture 21: MALDI-TOF and Sensitire Flashcards

1
Q

MALDI-TOF is used to accurately and rapidly identify ___ and ___from clinical specimen or other sources

A

Bacteria, fungi

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2
Q

MALDI-TOF is a ___technique that uses a laser energy absorbing matrix ___ to create ions from large molecules with minimal fragmentation

A

Ionization, HCCA

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3
Q

What is time of flight

A

Time required to travel a distance through a medium

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4
Q

How does MALDI-TOF identify bacteria

A

Measures highly abundant proteins found in microorganisms and compares them to database

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5
Q

What are the MALDI-TOF reagents and supplies

A
  1. Target plate
  2. Toothpicks
  3. Target position
  4. HCCA matrix
  5. BTS
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6
Q

What does HCCA matrix do

A

Lyses bacterial cell walls and extract proteins, absorbs layer energy and plays role in desorption and ionization

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7
Q

What is BTS

A

Bacterial test standard used for calibration and quality control
Use E. Coli

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8
Q

What is calibration

A

Process to maintain accuracy of instrument. Configures instrument to provide result for a sample within an acceptable range

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9
Q

What is quality control

A

Way to maintain standards in manufactured products by testing a sample against the specification. Measures test performance

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10
Q

What are the MALDI-TOF steps for bacterial identification

A
  1. Collect sample
  2. Culture and incubate
  3. Examine plate for growth
    4a. If pure culture- proceed to MALDI-TOF
    4b. If mixed culture- subculture and then proceed to MALDI-TOF
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11
Q

What are the 3 types of extraction (lysis) methods

A
  1. Direct smear
  2. Formic acid extraction (smear/formic acid/ HCCA)
  3. Tube extraction (methanol/ acetonitrile/ formic acid)
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12
Q

How do you extract bacteria that produce a capsule or have excess exopolysaccharide matrix

A

Short/ 5 minute formic acid-acetonitrile extraction and centrifugation step before application on target plate

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13
Q

What is the purpose of the extracted method

A

Helps release internal proteins that can’t be extracted by matrix solution (HCCA) allowing for more efficient ionization and thus higher quality identification

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14
Q

What does a MALDI-TOF range of 2-3 indicate and what color would it be on results sheet

A

High confidence identification
Color: green

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15
Q

What does a MALDI-TOF range of 1.7-1.99 mean and what color

A

Low confidence identification
Color: yellow

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16
Q

What does a MALDI-TOF range of 0-1.69 mean and what color

A

No organism identification possible
Color: red

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17
Q

What does a category A MALDI-TOF result mean

A

High consistency: best match is a high confidence match. Second best match is high confidence in which species is identical to best match. Low confidence identification in which species or genus is identical to best match, or non-identification

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18
Q

What does a MALDI-TOF category B result mean

A

Low consistency- requirements for high consistency not met. Best match is a high or low confidence identification. Second best match is a high or low confidence identification in which genus is identical to best match or non-identification

19
Q

What is a category C MALDI-TOF result

A

No consistency- requirements for high or low consistency not met

20
Q

What could have occurred to result in no organism identification possible

A
  1. Organism not in MALDI-TOF database
  2. Too much bacterial cells on target plate
  3. Too little bacterial cells on target plate
  4. Reagent failure
  5. No peaks found- problem with preparation
21
Q

What are some advantages to MALDI-TOF

A
  1. Fast- 45 minutes
  2. Minimal sample preparation time
  3. No gram stain required
  4. Low cost
  5. Non-expert identification
22
Q

What are some limitations of MALDI-TOF

A
  1. Data base dependent
  2. Unable to discriminate phyletically related microorganisms such as Shigella and E. Coli
23
Q

T or F: MALDI-TOF low confidence interpretations (1.7-1.99) means there are matches in MALDI-TOF database but matches did not meet established criteria for high confidence identification

24
Q

What is sensititre MIC system

A

Equipment used to perform anti microbial susceptibility tests based on MIC values

25
Q

What is principle of MIC

A

Determine lowest concentration possible to inhibit growth of test bacteria

26
Q

What are the materials needed for Sensitire MIC testing

A
  1. 0.5 McFarland polymer turbidity standard
  2. Water
  3. Mueller-Hinton broth
  4. Antibiotic panels
  5. Quality control organisms
  6. 18-24hr old pure culture of test bacteria
27
Q

What is the 0.5 McFarland polymer turbidity standard used for

A

To assure that the number of bacteria to test will be within given range

28
Q

What are the quality control organisms used for Sensititre MIC testing

A

E.coli, pseudomonas aerguinosa, S. Aureus, Enterococcus faecalis

29
Q

What is the COMPG1F Sensitire antibiotic panel

A

Used against gram positive organisms in companion animals
25 drugs

30
Q

What is the COMPGN1F sensititre antibiotic panel

A

Used against gram negative organisms in companion animals
19 drugs

31
Q

What is the EQUIN7F sensititre antibiotic panel

A

Used in horses
20 drugs

32
Q

What is the BOPO7F sensititre antibiotic panel

A

Used for cows and pigs
20 drugs

33
Q

What is the AVIAN1F sensititre antibiotic panel

A

Used for avian species
19 drugs

34
Q

What is the SMV1AMAF sensititre antibiotic panel

A

Used for mastitis
10 drugs

35
Q

What does it mean for sensititre result to be sensitive

A

Unable to grow in presence of particular antimicrobial concentration

36
Q

What does it mean for sensititre result to be resistant

A

Grows in presence of particular antimicrobial concentration or in the presence of a particular antimicrobial

37
Q

What does it mean for sensititre result to be intermediate sensitive

A

Higher dose of antimicrobial is needed to prevent growth

38
Q

What does it mean for sensitire result to be no interpretation

A

Insufficient pharmacological data is available to determine the break point for MIC test interpretation

39
Q

What is a breakpoint

A

Chosen concentration of antibiotic that defines whether a species of bacteria is susceptible or resistant to antibiotic

40
Q

Who determines breakpoint

A

US-FDA, center for drug evaluation and research

41
Q

What does the clinical laboratory standard institute do

A

Develop standard for clinical laboratory testing and in-vitro diagnostic test systems

42
Q

What are the advantages for Susceptibility testing

A
  1. Assure susceptibility of drug of choice and help select antimicrobial therapy
  2. Detect resistant
43
Q

What are some limitations to susceptibility testing

A
  1. In vitro can’t duplicate host environment
  2. Can’t include all biological variables within patient body
  3. Variability of drug distribution to infection site not considered
  4. Panel may not contain some preferred drugs
44
Q

T or F: no interpretation implies that the sensitire software was unable to interpret results and sign results to sensitive, resistant or intermediate

Microbiology (31 decks)

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