Authors : C.Khernane*1, M.Sadelaoud1, W.Toumi1, H.Benghzel1, A.Smail. 1 : M.SADELAOUD laboratory.
Performance of MALDI-TOF mass spectrometry for early identification of bacteria isolated from positive bloodculture bottles
Objectifs : The main objective of this study is to evaluate the performance of MALDI-TOF in the early identification of bacteria from positive bloodculture bottles, in comparison with conventional bacterial identification methods.
Matériel et méthodes : A single-center retrospective study was conducted on a cohort of 81 patients hospitalized between September 1, 2024 and March 9, 2025 for clinical suspicion of bacteremia, sepsis, or septic shock. A total of 81 bloodcultures were performed, regardless of the number of bottles collected per patient. Pathogen identification from positive blood cultures was performed by MALDI-TOF mass spectrometry. Confirmation of identifications was performed by Panel BLOOD Biofire multiplex PCR in a subgroup of cases, and by MALDI-TOF after bacterial culture on agar.
Résultats : Of a total of 81 bloodcultures analyzed, 34 (41,97%) were negative, 22 (27,16%) were considered contaminated, and 25 (30,86%) were positive. Among the 25 positive blood cultures, 20 were identified by MALDI-TOF mass spectrometry from positive Bact/ALERT bottles, while the others were identified by the conventional method. Of the 20 MALDI-TOF identifications, 14 obtained a high or acceptable identification score.
Bacterial species identified include: Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, Enterococcus faecalis, Pantoea spp, Staphylococcus epidermidis, Pseudomonas aeruginosa, Stenotrophomonas maltophilia, Acinetobacter baumannii. Among the 20 bloodcultures identified by MALDI-TOF, one discrepancy was observed for a bottle containing Staphylococcus aureus, for which identification could not be confirmed. The other discrepancies were associated with polymicrobial bloodcultures, including up to five different bacterial species. Preliminary results indicate that MALDI-TOF allows rapid and accurate bacterial identification, with a species-level concordance of 70% (14/20). Discussion : The results obtained confirm the performance of MALDI-TOF mass spectrometry for the rapid identification of pathogens from positive blood cultures, allowing a significant reduction in the time to initiate targeted antibiotic therapy. In accordance with literature data, the efficiency of MALDI-TOF identification is generally higher for Gram-negative bacteria than for Gram-positive bacteria. This difference could be attributed to a greater resistance to lysis of Gram-positive bacteria. The performance of MALDI-TOF for the identification of polymicrobial blood cultures remains a subject of debate. Although some authors report the ability of the technique to identify the different species present, others highlight the risk of detecting a single dominant species. Rapid and accurate identification of bacterial species by MALDI-TOF, including the distinction between Stenotrophomonas maltophilia and Enterobacteriaceae from Gram-negative blood cultures, could provide crucial information to guide the choice of antibiotic therapy.
Conclusion : The present study confirms the importance of MALDI-TOF mass spectrometry in the early diagnosis of bloodstream infections. Its performance in rapid identification makes it a valuable diagnostic tool for clinical microbiology laboratories, allowing optimized clinical management of patients.
