SelectScience Interview: Part 1: MALDI-TOF and the Clinical Microbiology Laboratory

How and why MALDI-TOF technology is being applied to microbial identification

23 Mar 2015

Dr. Robert Jerris is Director of Clinical Microbiology at the Children’s Healthcare of Atlanta Pediatric Hospital
Children’s Healthcare of Atlanta Pediatric Hospital
Children’s Healthcare of Atlanta is one of the largest clinical care providers for children in the country. It Manages more than half a million patient visits annually at three hospitals and 17 neighborhood locations.
I have to share with you that this is truly a game changer
Dr. Robert Jerris 

Atlanta Pediatric Hospital

In this interview, Dr. Robert Jerris, Director of Clinical Microbiology at the Children’s Healthcare of Atlanta Pediatric Hospital, discusses his experiences in implementing and using the MALDI Biotyper for clinical diagnostics use. In part one of our interview, Dr Jerris explains how this technology is a ‘game changer’ for the clinical laboratory, revolutionizing the microbiology lab and enhancing patient care. Learn about how MALDI-TOF works and how the technology is applied to microbiology identification.

Written transcription of a recorded interview from the ‘Advances in Laboratory Diagnostics’ podcast series

The FDA recently announced clearance of the Bruker MALDI Biotyper for clinical diagnostic use in the USA. We spoke to Dr Robert Jerris, Medical Director of Clinical Microbiology at the Children’s Healthcare of Atlanta Pediatric Hospital. Dr Jerris and his department have been using the MALDI Biotyper for clinical diagnostic use.

SN: Dr Jerris thank you for joining me.
RJ:  My pleasure Sonia, thank you for having me.

SN: Could you start by briefly describing to us how the MALDI Biotyper works?
RJ: In the United States there are two FDA approved MALDI-TOF instruments and as you indicated, I use the Bruker Biotyper. I’ve been using it in my laboratory for over three years now and so my remarks will be primarily towards the Bruker instrument. But when I discuss a little bit about the scientific endeavors and functions of the instrument, it will be general to all of the MALDI-TOF instruments out there.
The system is now widely used in clinical microbiology, in industrial microbiology, animal health and food safety, and it has become a broadly accepted lab standard for what I call the next generation and dare I say the revolutionary identification of micro-organisms.

I have to share with you that this is truly a game changer.

When we think about endeavors and things that have happened in microbiology and new systems, MALDI-TOF gives us an opportunity to integrate a technology directly into patient care, and I think that from here forth, all new technologies should have this goal. So when we think about MALDI-TOF in general we need to compare it back to the old methods that we use for identification, and these are conventional biochemical phenotypic testings, which are time consuming.

After an organism is grown on the plate you have to select that organism; you carry out a series of identification methods and it takes generally another day to get a definitive identification. Well, the show-stopper for MALDI-TOF is that the minute that you get an organism on the plate you can put it in the MALDI-TOF instrument and get that identification. So the systems out there have this capability of what we call ‘real-time’ identification’. The Bruker Biotyper system covers a broad range of bacteria gram negative, gram positive, aerobes, anaerobes, microaerobics, yeast, mycelial fungi, microbacteria. So now you’re looking at one platform for all the organisms that you can grow on plates.

The basic scientific principle with a MALDI Biotyper is that you get a proteomic fingerprint that has been correlated back to gene sequence identification of these organisms, so your identification is truly robust. The unique part about this is that it’s automatic; once that fingerprint is generated you run the organisms through the system and you get an identification.

Now the Bruker MALDI Biotyper, with its latest library has over 5,600 organisms or strains within there for identification, is very, very strong for all of the disciplines in microbiology. The neat thing about the Bruker system is that it supports what we call the ‘open microbiology’ concept. That’s really important for folks like me who have the Centers for Disease Control a couple of blocks up the road from me. Because I can gather organisms that may not be in the database and with this ‘open microbiology’ concept, it allows me to generate my own database from our regional isolates and from select strains from the Centers for Disease Control; i.e. reference isolates, to actually customize the library that’s devoted to children.

So, that’s the background of MALDI-TOF. Now if I could just take a second and walk through each one of the steps and really show the power of this instrument.

If we breakdown the components, first the sample - whether it be a bacteria or a fungus or a microbacteria - is mixed with a matrix on a template, and this matrix does a couple of things. It co-crystallizes the components that were placed on the plate, it actually ruptures the cells, liberates the proteins and then it functions as a buffer, and we’ll see how important that is in just a minute. So that’s the ‘M’ part of MALDI-TOF; the matrix.

Next the target is placed in the instrument, and this is general to any one of the MALDI-TOF instruments. So, the target is placed in the instrument and then a vacuum seal is applied. Next a laser is applied, the ‘L’ component of MALDI-TOF, and I think it’s important to note that this is a really soft laser and it causes the absorption and ionization of the components. The matrix absorbs energy from the laser, that energy is transferred into the sample as heat. Once that heat hits the matrix and all the components therein, the sample is desorbed and the charge ions flow through a tube. Desorption and the ionization are the ‘D’ and ‘I’ components of MALDI-TOF.

Next in real-time, the released ions travel through this vacuum tube where their mass is analyzed and those lighter ions travel faster, and therefore are detected earlier than the heavier ions; this is known as the ‘time of flight’. A detector at the end of the vacuum tube records when these ions hit and it makes a chart, or a fingerprint or a ‘mass spectrum’ hence the ‘MS' part of MALDI-TOF MS.

Now from a mass spec perspective, once we add the matrix and we hit it with the laser, we get abundant proteins. Most of these are of a low mass that can ionize readily. They stay intact, which is the beauty of this technology because it’s a soft ionization. That profile that is generated looks like a fingerprint and it is compared back to those of well characterized organisms as I’ve indicated earlier, then that spectrum typically includes genus or genus species specific-peaks so that you get a comprehensive identification irrespective of what the organism is.

The bioinformatics in this system are quite robust as I’ve mentioned, over 5,600 organisms, and definitive identifications are then effected for all organism groups.

So that’s really a quick summation of how the MALDI-TOF works and the definition of its components.

Read Part 2: The challenges and hurdles of integrating MALDI-TOF, and its impact on patient care

Listen to the podcast interview