Rapid Identification of Positive Blood Cultures by Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry Using Prewarmed Agar Plates

Abstract

bThis study describes an inexpensive and straightforward method for identifying bacteria by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) directly from positive blood cultures using prewarmed agar plates. Different inoculation methods and incubation times were evaluated to determine the optimal conditions. The two methods using pelleted material from positive culture bottles performed best. In particular, the pellet streak method correctly identified 94% of the Gram negatives following 4 h of incubation and 98% of the Gram positives following 6 h of incubation.

MALDI-TOF mass spectrometry following short incubation on a solid medium is a valuable tool for rapid pathogen identification from positive blood cultures

“…To that end, we performed MALDI-TOF MS after a short incubation (4 h) of positive blood culture broths on a solid medium, an approach which has been described by only few recent reports so far (Bhatti et al, 2014;Idelevich et al, 2014;Verroken et al, 2015). Our data confirm and extend those studies.…”

Identification of bacteria from aerobic and anaerobic blood cultures after short cultivation by matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry

“…Our method complements a recently published protocol on detecting bacteria from blood cultures, which also utilized short cultivation of concentrated bacterial suspension on prewarmed agar plates (Bhatti et al, 2014). Our results provide independent evaluation of this approach for another major brand of MALDI-TOF instruments (MALDI Biotyper) and slightly different incubation and centrifugation conditions.…”

“…30 % (12/39) of coagulase-negative staphylococci (CoNS). Difficulties with direct MALDI-TOF based identification of CoNS from blood cultures have been described (Bhatti et al, 2014;Croxatto et al, 2012;Ferreira et al, 2011;Idelevich et al, 2014;La Scola, 2011;Mestas et al, 2014;Rodríguez-Sánchez et al, 2014) and are apparently independent of the method used. Prolonging the time of plate incubation has been shown to improve the identification rate of CoNS (Bhatti et al, 2014;Idelevich et al, 2014) and this approach is therefore likely to improve the performance of our method as well.…”

MALDI-TOF Mass Spectrometry for Microorganism Identification

“…While Gramnegative bacteria appear to be adequately identified after an incubation period of 2-4 h, Gram-positive bacteria require 6 h of incubation (Bhatti, Boonlayangoor, Beavis, & Tesic, 2014;Idelevich et al, 2014;Verroken et al, 2014). However, use of an ethanol/formic acid extraction was shown to reduce the incubation required for Gram-positive microorganisms to 3 h (Idelevich et al, 2014).…”