Detection of carbapenemase activity directly from blood culture vials using MALDI-TOF MS: a quick answer for the right decision.

OBJECTIVES Recently, matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS) was successfully applied for the detection of carbapenemase activity directly from Gram-negative colonies. Based on this principle, we evaluated the performance of MALDI-TOF MS for rapid detection of carbapenemase activity directly from positive blood culture vials. METHODS A total of 100 blood culture vials were randomly selected. MALDI-TOF MS carbapenemase assay results were confirmed by the detection of carbapenemase-encoding genes. RESULTS A total of 110 bacterial isolates were recovered. The MALDI-TOF MS carbapenemase assay identified 21 of 29 (72.4%) of the carbapenemase-producing isolates directly from the blood culture vials, especially those encoding KPC-2 (100%) and SPM-1 (100%), after a 4 h incubation period. Although the majority of OXA-23-producing Acinetobacter baumannii isolates were not identified on day 1, all isolates were identified as carbapenemase producers directly from the colony on the next day. CONCLUSIONS The MALDI-TOF MS carbapenemase assay is a feasible and rapid test to identify carbapenemase activity directly from blood culture vials. It may contribute to faster readjustment of empirical antimicrobial therapy and implementation of infection control measures.