The use of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for rapid bacterial identification in patients with smear-positive bacterial meningitis

Abstract

Objectives: To assess the potential of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) in rapid identification of bacteria from smear-positive cerebrospinal fluid (CSF) in a cohort of patients with meningitis.

Methods: Single-centre observational study, including adults and children with community-acquired or postneurosurgical bacterial meningitis. Meningitis was defined using established criteria. Samples of CSF that had a positive CSF Gram stain were directly examined by MALDI-TOF-MS. Identification was considered accurate when identical to the CSF culture or PCR results (species and genus level). Laboratory workers performing the MALDI-TOF-MS and interpreting its results were blinded to the direct smear results, except for the fact that it was positive. MALDI-TOF-MS results were not conveyed to clinicians.

Results: MALDI-TOF-MS was tested on 44 CSF samples; ten samples were obtained from patients with community-acquired meningitis, and 34 samples were from patients with postneurosurgical meningitis. The assay identified bacteria correctly in 17/21 of the samples with Gram-negative rods observed on the direct smear, all obtained from patients who had undergone neurosurgery, (sensitivity 81%, 95% CI 64.2%-97.7%). In the postneurosurgical group, Gram-positive cocci were identified correctly in only 1/11 (9.1%) of the samples, and Candida species were not identified in two samples. Among patients with community-acquired meningitis, the assay did not identify Streptococcus pneumoniae in eight of eight samples, Neisseria meningitidis in one sample (1/1), and Streptococcus agalactiae in one sample (1/1).

Conclusions: We found MALDI-TOF-MS to be useful in the rapid identification of Gram-negative rods directly from smear-positive CSF samples, but not of Gram-positive bacteria.

Keywords: Cerebral spinal fluid; Diagnosis; Gram-negative rods; MALDI-TOF-MS; Meningitis; Postneurosurgical.