Lecture 20: Lab and Optimizing Patient Care Flashcards
bacterial identification: PCR
- does not tell us how to treat
- moderately time consuming
- you need to know what it is before you test it
Types of bacterial identification
- bacterial morphology (1700s)
- gram stain (1884)
- metabolic activity
- molecular methods
metabolic activity
- diff identifying organisms that grow slowly and/or anaerobes
- challenging you have organisms that do not ferment or metabolize sugars readily
- takes long (6-48 hrs) to identify
molecular identification
- excellent identifications, expensive to perform
- takes hours to days
- great deal of infrastructure and specialize staff
- cannot use in polymicrobial specimens - will not know for hours/days
- require specialized primers for some bacterial species
Enter- The MALDI-TOF
stands for:
M-atrix
A-ssisted
L-aser
D-esorption/I-onization
T-ime
O-f
F-light
Spectroscopy
- protein fingerprint of the bug
- most academic centers will have this
- some community hospitals will too
- changed how we identify organisms in microbiology
- relies on organism protein signatures
- clinical databases approved by regulatory bodies
How does The MALDI-TOF work
- matrix assisted - goopy thing immobilized bacteria
- has laser
- laser shoots @ bacteria, makes it into a cloud
- cloud travels to a detector
- thru a vacuum
- discriminates size and charge and rate of cloud hits it
- makes spectrum basically blow it up, so we can identify bug
How does The MALDI-TOF work
- matrix assisted - goopy thing immobilized bacteria
- has laser
- laser shoots @ bacteria, makes it into a cloud
- cloud travels to a detector
- thru a vacuum
- discriminates size and charge and rate of cloud hits it
- makes spectrum basically blow it up, so we can identify bug
output and analysis of The MALDI-TOF
- spectrograph is created by organism is compared to a database in real time
- organism ID w a “score of confidence” assigned to it is provided to the user
pros of The MALDI-TOF
- fast (16 organisms/35 min)
- cheap
- easy to use
- able to ID metabolically inert organisms (non-fermenters)
- able to ID fastidious organisms, not much organism is required
- one stop shop for all bugs: aerobes, anaerobes, fermenters, and yeasts
- no primers or probes
- does not need an instrument
The MALDI-TOF cons
- if organism not in database - cannot ID it
time to process blood cultures pre The MALDI-TOF
- 5 days in blood culture instrument
- incubated 18-24 hrs
- bacterial ID (6-24 hrs)
- monday take the blood - thus you get results
24-48 hrs for aerobes and facultative organisms
rapid blood culture identification protocol
- 5 days in blood culture instrument
- incubate 4 hrs
- ID 30 min
- total time 6 hrs
take culture monday, tues its flagged, can be identified by tues evening
this is how MALDI changed things
optimizing blood cultures on The MALDI-TOF
- blood cultures unique bc they are 1st incubated in specialized culture media before they are identified in specialized culture media
(high organism load, usually high volumes) - majority tend to be mono-microbial
- no “normal flora” - sterile environment
- significant impact on patient care
clinical impact of The MALDI-TOF
- great organism identifications
- organisms have diff intrinsic resistance - so knowing the organism’s identity is important for guiding therapy
- for every hr that appropriate antibiotics are delayed survival decreases 7.6% - in septic patients
impact on patients of The MALDI-TOF
- decreased length of hospital stay
- saved us on resistance bc less use of broad spectrum antibiotics
- diff to measure impact on mortality
- reduction in mortality attributed to BSI’s
