A-240 Rapid and Reliable Identification of Microorganisms from Early Growth of Positive Blood Cultures Using MALDI-TOF Mass Spectrometry

Abstract

Abstract Background Rapid identification of organisms causing bloodstream infections is critical for treatment. Traditional workflows rely on 18–24 h growth of isolated colonies. Our objective was to evaluate identification of early growth using Bruker and VITEK® MS PRIME MALDI-TOF systems. Materials Positive blood cultures (BACT/ALERT® FA/FN Plus; bioMérieux VIRTUO®) were included if bottles were positive <8 h and had time-to-positivity of <40 h. Broths were sub-cultured to blood agar and incubated at 35°C/5% CO2. MALDI-TOF identification of 6–8 h growth (short incubation, SI) and 18–24 h growth (standard incubation, SDI) was performed by a high (HEU, >1 year) and low (LEU, <1 month) experience user. Each identification was performed using standard set-up for Bruker and VITEK MS PRIME, and target set-up using VITEK PICKMETM pen. Identification level and time-to-result (TTR) were measured and compared using Fisher’s exact and t-test. Results 53 organisms (36 Gram-positive, 15 Gram-negative, 2 yeast) were isolated from 50 blood cultures. The HEU achieved species-level identification for 87% on VITEK MS PRIME using routine set-up and PICKME after SI vs 74% on Bruker, while 66% and 70% of organisms were identified on VITEK MS PRIME vs 75% on Bruker by the LEU (Table). After SDI, ≥94%(HEU) and ≥87%(LEU) of organisms were identified, with no differences noted by set-up or user experience (P > 0.05). Species-level identification after SI was higher for Gram-negative (100%) vs Gram-positive (67–86%) organisms for the HEU. PICKME pen usage increased identifications to 100% from 67% for Gram-negatives for the LEU. For mixed cultures (n = 3), only 1 of 2 organisms was identified after SI. TTR was significantly longer(P < 0.05) for SI vs SDI and Bruker vs VITEK MS PRIME for the HEU. Conclusions Identification of microorganisms after short incubation on solid media achieves early, reliable identification for a majority of positive blood cultures without need for additional hands-on time or extraction.