NACB - Scientific Shorts
NACB - Scientific Shorts (formerly NACB Blog)
By Christopher Doern Ph.D
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Microbiology has traditionally been a laboratory discipline with prolonged result turn-around times because growing the organisms has always been necessary for identification.  The practice of identifying viruses has recently been revolutionized by the discovery of molecular techniques such as PCR that can be completed in hours as opposed to days or weeks.  Still, molecular techniques remain expensive, require special instrumentation and are technically challenging to perform.  As a result, it is not a practical method for routine identification of bacteria and microbiologists are identifying organisms today in much same way they were 30 years ago. 

Recently, an old chemistry technique (mass spectrometry) has been improved and adapted to identify bacteria and yeast in a rapid and inexpensive manner.  This technique, matrix-assisted laser desorption ionization – time of flight, or MALDI – TOF, relies on laser ionization of the proteins that make up the organism.  Identifications are generated based on comparing the resulting protein profile or “protein finger print” of the organism to a reference database of protein fingerprints.  Because this technology does not rely on growth characteristics of the organism the method is extremely rapid and requires only a very small quantity of test organism. What used to take days, now takes minutes.  Also, in contrast to current methods there is virtually no consumable cost.  The process of biochemically identifying an organism that used to cost $5 - $10 (OR MORE) and take anywhere from 1 to 3 days, now costs about 50 cents per test and takes about 15 minutes.  Having the ability to rapidly generate these results will allow physicians to optimize their treatments days earlier than they do now with current methods.

Although the cost and time savings of MALDI-TOF promises to revolutionize the way we practice microbiology, perhaps the most exciting prospect is the ability to identify organisms out of positive blood cultures.   Bacteria and yeast growing in a patient’s blood (bacteremia and fungemia, respectively) is a medical emergency.  We currently diagnose this by placing a patient’s blood into a bottle and incubating that blood.  An instrument monitors these bottles continuously and alerts us when an organism grows to a point that it can be detected.  At this point we know the patient may have a life threatening illness but we know very little about the causative organism.   With some brief processing (~30 minutes) MALDI-TOF can be applied to these samples and identify the organism growing in the patient’s blood.  This will provide valuable information to the treating physician days or even weeks earlier than with current practices resulting in a marked improvement in patient care.

Lastly, the applications mentioned above are well described, but they are just a few of the functions this instrument is expected to be able to perform.  As research continues it is anticipated that we’ll be able to generate other important results with MALDI-TOF.  Examples include determining what antibiotic a particular organism might be resistant to, typing of organisms to tell if they are the same or different in outbreak investigations and identification directly from specimens with high organism burden such as in urinary tract infections.

This technology has already been widely accepted in Europe and is just now being introduced in the United States.  Only a handful of laboratories have adopted this technology here but in five years it is expected that MALDI-TOF will be the new standard in bacterial and fungal identification.  It is a rare advance in technology that will allow us to do things better, faster and cheaper.
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