MALDI & Sensititre Flashcards
What is MALDI-TOF MS?
Laboratory equipment for accurate and rapid identification of bacteria and fungus from clinical specimen and other
sources
How does MALDI-TOF MS work?
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
Define time of flight
time required to travel a distance through a medium
What are the specific signatures that are read based on?
bacterium specific biomarkers - proteins, peptides, lipids, RNA, and DNA
Is MALDI measuring high or low abundant proteins within the microorganism?
high
What is the purpose of the HCCA matrix in MALDI-TOF?
lyses bacterial cell wall and extracts proteins > protein molecules embedded in dried crystal matrix
plays a role in desorption and ionization
what is BTS in MALDI-TOF?
bacterial test standard for calibration and quality control
Escherichia coli used
Can a mixed culture be used for MALDI-TOF?
no must be a pure culture
what must be done if the bacteria has a capsule or excess exopolysaccaride matrix
processing through short formic acid-acetonitrile extraction and centrifugation step
Define high consistency for MALDI-TOF
best match - high-confidence
second best match - high confidence with identical species, low confidence with species or genus identical, non-identification
Define low consistency for MALDI-TOF
high consistency not met
best match - high or low confidence identification
second best match - high or low confidence identification with genus identical, non-identification
What does it mean when no organism identification is possible for MALDI-TOF?
organism not in MALDI-TOF MS database
too much bacteria on target plate
not enough bacteria on target plate
reagent failure
what does it mean when there are no peaks found for MALDI-TOF?
problem with sample preparation
what are the advantages to MALDI-TOF?
what are the limitations to MALDI-TOF?
True
what is sensititre?
a laboratory equipment used to perform antimicrobial (drug) susceptibility tests based on the principles of minimum inhibitory concentration (MIC) values. Fully automated.
How is the number of bacteria tested for sensititre assured?
0.5 McFarland polymer turbidity standard = 1.5 x 10^8 cfu/ml
What does S, R, I, and NI mean for sensititre results?
Define breakpoint for sensitire
chosen concentration of antibiotic that defines wether bacteria is susceptible or resistant
determined by US-FDA
Which antimicrobials are more effective - ones with low MIC or high MIC?
low MIC more effective than high MIC
Means no interpretation
Over time interpretation will be established by CLSI
Can still use b/c MIC was small but at your own discretion
What are the advantages and disadvantages of sensititre?
False - it was interpreted there is just no break point value set
