Instant screening and verification of carbapenemase activity in B fragilis in positive blood culture, using Matrix-Assisted Laser Desorption Ionization- Time of Flight Mass Spectrometry (MALDI-TOF-MS).

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Instant screening and verification of carbapenemase activity in B fragilis in positive blood culture, using Matrix-Assisted Laser Desorption Ionization- Time of Flight Mass Spectrometry (MALDI-TOF-MS).

J Med Microbiol. 2014 May 21;

Authors: Johansson A, Nagy E, Sóki J

Abstract
Rapid identification of isolates in positive blood cultures are of great importance to secure correct treatment of the septicemic patient. As antimicrobial resistance is increasing, rapid detection of resistance is crucial. Carbapenem resistance in Bacteroides fragilis (B. fragilis) associated with cfiA-encoded class B metallo-beta-lactamase is emerging. In our study we spiked blood culture bottles with twenty-six B. fragilis strain with various cfiA-status and ertapenem MICs. By using main spectra (MSP) specific for cfiA-positive and -negative B. fragilis strains, isolates could be screened for resistance. To verify strains that were positive in the screening, a carbapenemase assay was performed where the specific peaks of intact and hydrolyzed ertapenem were analyzed with MALDI-TOF MS. We here show that it is possible to correctly identify B. fragilis and to screen for enzymatic carbapenem resistance directly from the pellet of positive blood cultures. The carbapenemase assay to verify the presence of the enzyme was successfully performed on the pellet from the direct identification despite the presence of blood components. The result of the procedure was achieved in 3h. Also the Bruker MSBL Prototype Software was proven to be based on an algorithm which correlates with the manual inspection of the spectra, but also improves the interpretation by showing the variation in the dataset.

PMID: 24850880 [PubMed - as supplied by publisher]