MALDI & Sensititre

Question 1

What is MALDI-TOF MS?

Answer 1

Laboratory equipment for accurate and rapid identification of bacteria and fungus from clinical specimen and other
sources

Question 2

How does MALDI-TOF MS work?

Answer 2

ionization technique that uses laser energy absorbing matrix (HCCA) > laser-infrared to target letting it desorb and ionize> ions from large molecules with minimal fragmentation > travels up flight tube to detector > spectrum created based off biomarkers > compared in data base to known organisms

Question 3

Define time of flight

Answer 3

time required to travel a distance through a medium

Question 4

What are the specific signatures that are read based on?

Answer 4

bacterium specific biomarkers - proteins, peptides, lipids, RNA, and DNA

Question 5

Is MALDI measuring high or low abundant proteins within the microorganism?

Answer 5

high

Question 6

What is the purpose of the HCCA matrix in MALDI-TOF?

Answer 6

lyses bacterial cell wall and extracts proteins > protein molecules embedded in dried crystal matrix
plays a role in desorption and ionization

Question 7

what is BTS in MALDI-TOF?

Answer 7

bacterial test standard for calibration and quality control
Escherichia coli used

Question 8

Can a mixed culture be used for MALDI-TOF?

Answer 8

no must be a pure culture

Question 9

what must be done if the bacteria has a capsule or excess exopolysaccaride matrix

Answer 9

processing through short formic acid-acetonitrile extraction and centrifugation step

Question 10

Define high consistency for MALDI-TOF

Answer 10

best match - high-confidence
second best match - high confidence with identical species, low confidence with species or genus identical, non-identification

Question 11

Define low consistency for MALDI-TOF

Answer 11

high consistency not met
best match - high or low confidence identification
second best match - high or low confidence identification with genus identical, non-identification

Question 12

What does it mean when no organism identification is possible for MALDI-TOF?

Answer 12

organism not in MALDI-TOF MS database
too much bacteria on target plate
not enough bacteria on target plate
reagent failure

Question 13

what does it mean when there are no peaks found for MALDI-TOF?

Answer 13

problem with sample preparation

Question 14

what are the advantages to MALDI-TOF?

Answer 14

Question 15

what are the limitations to MALDI-TOF?

Answer 15

Question 16

Answer 16

True

Question 17

what is sensititre?

Answer 17

a laboratory equipment used to perform antimicrobial (drug) susceptibility tests based on the principles of minimum inhibitory concentration (MIC) values. Fully automated.

Question 18

How is the number of bacteria tested for sensititre assured?

Answer 18

0.5 McFarland polymer turbidity standard = 1.5 x 10^8 cfu/ml

Question 19

What does S, R, I, and NI mean for sensititre results?

Answer 19

Question 20

Define breakpoint for sensitire

Answer 20

chosen concentration of antibiotic that defines wether bacteria is susceptible or resistant
determined by US-FDA

Question 21

Which antimicrobials are more effective - ones with low MIC or high MIC?

Answer 21

low MIC more effective than high MIC

Question 22

Answer 22

Means no interpretation
Over time interpretation will be established by CLSI
Can still use b/c MIC was small but at your own discretion

Question 23

What are the advantages and disadvantages of sensititre?

Answer 23

Question 24

Answer 24

False - it was interpreted there is just no break point value set