How MALDI-TOF-MS makes mycobacterium diagnosis faster and more accurate

-

The laboratory I work in has plenty of instruments that help us characterise and identify microorganisms causing diseases in patients. One of my current projects is to validate an instrument called "matrix-assisted laser desorption ionization-time of flight mass spectrometer" (MALDI-TOF-MS) in identifying members of the Mycobacterium species. Many of these organisms are opportunistic, meaning they only cause illnesses in people whose immune systems are not strong enough to fight infections. Mycobacterium leprae is known for causing leprosy, but we cannot grow this bacterium in culture media, so we cannot isolate it. Mycobacterium tuberculosis complex, on the other hand, is a group of several species of Mycobacterium that causes tuberculosis. Tuberculosis is a disease that killed 1.6 million people in 2021 alone. It is a leading cause of death globally, second only to COVID-19 since the pandemic began.

Identifying the Mycobacterium species that has infected a patient is challenging because (1) this group of organisms require additional inactivating treatments, such as exposure to high temperatures (e.g., 121ºC for 15 minutes), to ensure that they cannot cause disease to the laboratorians; and (2) the method of choice for identifying mycobacteria (high-performance liquid chromatography, HPLC) has a limited library of chromatograms. This method can tell if a specimen has M. tuberculosis and other mycobacteria based on mycolic acid chromatograms. However, it won't be able to identify mycobacteria whose mycolic acid profiles are not included in the library.

Enter MALDI-TOF-MS. 

This technique separates ribosomal proteins by ionizing them and allowing them to travel in a time-of-flight tube. The separation of proteins is based on mass-to-charge ratios, if I understand correctly. The concentration of each separated protein then provides the mass spectrum, which is unique to each mycobacterium. The mass spectrum is compared to a library of mass spectra via a computer software. The software bases the identification on a "confidence score".

The MALDI-TOF-MS has several advantages over the HPLC. First, the library used by the MALDI-TOF-MS software is more extensive than the library used for HPLC. This is important because it lessens the number of misidentification events (particularly of organisms that are highly related). Second, if the inactivation of mycobacteria and the extraction of ribosomal proteins are conducted using a commercially available kit, the method becomes less error-prone. This can be attributed to the one-time inoculation of biomass into a microfuge tube. In comparison, several sample transfers during the sample preparation for HPLC increase the chances of creating errors during the preparation. Third, the streamlined methodology (from the kit) is much shorter than the sample preparation for HPLC.

I'm excited to say that the MALDI-TOF-MS just might live to see the day when more microbiologists in the laboratory can use the instrument routinely.

Comments

Post a Comment

Thank you for dropping by!

Before moving on, please share your thoughts or comments about the post. :)

Thanks again!

Popular posts from this blog

Skyflakes

-
One of the more famous Philippine exports is Skyflakes , a wheat-based, salty cracker. It is one of my emergency food items: I typically have some stocked at home and in my handbag in case I become hungry (like in traffic jams). When there's no electricity and it's impractical to cook rice (because the leftover would spoil), I'd open a pack of Skyflakes and generously coat each cracker with Cheez Whiz... if I had a bottle of it within reach. Anyway, each time I spent more than two weeks outside the Philippines, I'd be elated to see boxes of Skyflakes inside Asian stores (particularly when in I was Australia and in the USA). Back then, I took it as a sign of homesickness. When I moved to California, I didn't miss Skyflakes because Mommy made sure that there's a steady supply in the house. Skyflakes is embedded in Filipino gastronomy as a snack, a panawid-gutom , that anyone who reacts positively upon seeing Skyflakes outside the Philippines must have spe
Read more

10 things I learned while driving on Marcos Highway to Baguio City

-
I went on a day trip to the City of Pines, which was around a 700-km drive from my house. I drove  going up there and then from the city to Victoria, Tarlac. After that, my dad took over the driving duties. It was day trip with Tita Ising and Tito Sibing with us. Anyway, this trip was my first time to go to Baguio City with me behind the wheel. As everyone who drives up knows, there are three main routes to Baguio from the lowlands: Kennon Road, which ascends from Rosario, La Union. It was out of my options because it's too dangerous to use that road in the rainy season. The second route is via Naguilian Road, which makes my trip a lot longer because the beginning of the ascent is in Bauang, La Union (further north). The last route, and the one I took, was the Marcos Highway, now known as the Aspiras-Palispis Highway. This 47-km road starts from Agoo, La Union and is touted as the safest route among the three.  As I drove up and then down (on the same day; we were in Bagu
Read more

Surat Mangyan

-
Image
In high school, part of the Filipino curriculum was learning about one of the country's ancient native scripts called Baybayin . I learned back then that this script was eventually abandoned because the Spanish, and eventually the Americans, encouraged the use of the Latin script for written communications. But that's in the lowlands; the rules were different up in the mountains. In the lush mountains of Mindoro, groups of indigenous people called Mangyans  live largely in isolation away from the Christianised Filipinos. This isolation has led to the continuous development of the Mangyans' old script, Surat Mangyan . As I walked inside the Ayala Museum , I saw this bamboo tube (I'm not sure if it's an instrument) with Mangyan script written all over it. I suppose that this was equivalent to a book or a song. But I haven't figured out what's written yet, despite the translation guide provided. What I can do, however, is write my name in Ma
Read more