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From the bench, a view of MALDI-TOF mass spec

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Anne Ford

February 2015—Melissa Jones, MT(ASCP), doesn’t mince words—not when it comes to MALDI-TOF MS.

“It’s going to revolutionize the way you do microbiology in your laboratory, and you’re absolutely going to love it,” said Jones, who is a microbiology specialist for clinical microbiology and immunology at McLendon Clinical Laboratories at University of North Carolina Hospitals, Chapel Hill.

She should know. Jones recently oversaw the implementation of MALDI-TOF mass spectrometry in the UNC laboratory, which processes about 31,000 blood cultures and about 39,000 urine cultures each year. The experience left her with a deep appreciation of the technology and an intimate knowledge of how to best introduce and use it. And she shared UNC’s experience last year in an American Society for Microbiology General Meeting session.

The UNC laboratory began its MALDI-TOF journey by evaluating two systems: the MALDI Biotyper from Bruker and the Vitek MS from BioMérieux. Though the laboratory eventually chose to implement the Vitek MS, “I can tell you from experience they are both fantastic systems,” she said. “It really doesn’t matter which one you choose.”

From the get-go, Jones and her team knew they wanted to go live with Gram-negative rods, staphylococci, and other common organisms first, “so we can get the biggest bang for our buck,” she said. As for the number of isolates tested, the first verification study saw the testing of about 60 Enterobacteriaceae, 12 Pseudomonas aeruginosa, and 41 Staphylococcus species, among others. “We did this on a variety of appropriate media and at at least two time points, so for Gram-negative rods we would have tested them on, say, Chocolate agar, Sheep blood agar, and MacConkey agar and at least one overnight and two overnights.”

What happens if no identification is made? Re-fire on the same spot, Jones said. In her experience, that will solve the problem about half of the time for these normal organisms. If it doesn’t, she advised re-spotting the same day. “If those two things don’t resolve your issue, then go back and look at the course of your verification study,” she suggested. “If your failed spot was, say, a Pseudomonas on MacConkey at 24 hours, likely you tested many Pseudomonas at 24 hours on MacConkey, and one failed spot in the midst of all that is perfectly fine.”

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