Reducing time to identification of aerobic bacteria and fastidious micro-organisms in positive blood cultures.

Rapid and early identification of micro-organisms in blood has a key role in the diagnosis of a febrile patient, in particular, in guiding the clinician to define the correct antibiotic therapy. This study presents a simple and very fast method with high performances for identifying bacteria by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) after only 4 h of incubation. We used early bacterial growth on PolyViteX chocolate agar plates inoculated with five drops of blood-broth medium deposited in the same point and spread with a sterile loop, followed by a direct transfer procedure on MALDI-TOF MS target slides without additional modification. Ninety-nine percentage of aerobic bacteria were correctly identified from 600 monomicrobial-positive blood cultures. This procedure allowed obtaining the correct identification of fastidious pathogens, such as Streptococcus pneumoniae, Neisseria meningitidis and Haemophilus influenzae that need complex nutritional and environmental requirements in order to grow. Compared to the traditional pathogen identification from blood cultures that takes over 24 h, the reliability of results, rapid performance and suitability of this protocol allowed a more rapid administration of optimal antimicrobial treatment in the patients. SIGNIFICANCE AND IMPACT OF THE STUDY: Bloodstream infections are serious conditions with a high mortality and morbidity rate. Rapid identification of pathogens and appropriate antimicrobial therapy have a key role for successful patient outcome. In this work, we developed a rapid, simplified, accurate, and efficient method, reaching 99 % identification of aerobic bacteria from monomicrobial-positive blood cultures by using early growth on enriched medium, direct transfer to target plate without additional procedures, matrix-assisted laser desorption ionization-time of flight mass spectrometry and SARAMIS database. The application of this protocol allows to anticipate appropriate antibiotic therapy.