Direct inoculation method for identification and antimicrobial susceptibility testing using matrix-assisted laser desorption ionization-time of flight mass spectrometry and both the Vitek 2 and MicroScan Walkaway 96 Plus systems

Maryann Brandt; Kimberly McCullor; Don Harris; Zachary Ratzlaff; Eric Thompson; Cory M Pfeifer

doi:10.1080/08998280.2023.2169556

Direct inoculation method for identification and antimicrobial susceptibility testing using matrix-assisted laser desorption ionization-time of flight mass spectrometry and both the Vitek 2 and MicroScan Walkaway 96 Plus systems

Proc (Bayl Univ Med Cent). 2023 Feb 8;36(3):354-359. doi: 10.1080/08998280.2023.2169556. eCollection 2023.

Authors

Maryann Brandt¹, Kimberly McCullor², Don Harris³, Zachary Ratzlaff³, Eric Thompson³, Cory M Pfeifer⁴

Affiliations

¹ Microbiology Laboratory, Phoenix Children's, Phoenix, Arizona.
² Michigan Department of Health and Human Services, Bureau of Laboratories, Lansing, Michigan.
³ Norman Regional Hospital, Microbiology Laboratory, Norman, Oklahoma.
⁴ Department of Radiology, Phoenix Children's, Phoenix, Arizona.

Abstract

The aim of our study was to evaluate a protocol utilizing serum separator tubes (SST) to facilitate a faster, cost-effective, direct method for rapid sensitivity testing and identification of positive blood cultures. Spiked cultures were inoculated into either Becton Dickinson (BD) BACTEC^TM Aerobic Plus or Anaerobic/F bottles containing sterile human blood. Bottles were immediately processed when positive. A parallel study using patient isolates was used in which bacteria were pelleted by SST from positive blood cultures. For identification, a portion of the pellet was tested by matrix-assisted laser desorption/ionization as described by the manufacturer. MicroScan panels and Vitek 2 results were compared. Categorical agreement was used as comparison to standard subculture and/or polymerase chain reaction methods. No discordant identifications were observed, and 86% generated a successful identification when compared to subculture methods. For the Vitek 2, we observed a 99% essential agreement when compared to the subculture method. For the MicroScan Walkaway, we observed 94.9%, 97.4%, and 100% categorical agreement for MIC panels 53, 38, and MICroSTREP Plus 2, respectively. Turnaround times were reduced from 4 hours for identification and 11 hours for antimicrobial sensitivity testing. We conclude that the SST method results in timelier, actionable results for antimicrobial stewardship initiatives.

Keywords: Antimicrobial susceptibility testing; clinical microbiology.