Analytical performance of an assay for ergosterol, a potential biomarker for Naegleria fowleri in cerebrospinal fluid.

INTRODUCTION

Naegleria fowleri is a pathogenic free-living amoeba that causes primary amoebic meningoencephalitis, a rare and difficult-to-diagnose form of meningitis. By testing patient cerebrospinal fluid (CSF) for ergosterol, a membrane component unique to fungi and amoeba, cases of primary amoebic meningoencephalitis may be distinguished from cases of bacterial and viral meningitis.

METHODS

Pooled CSF was fortified with ergosterol, extracted, filtered, and measured by liquid chromatography-tandem mass spectrometry. Measurement method precision, sensitivity, recovery, and stability were evaluated. In vitro cell cultures of N fowleri and a sample (n = 200) of deidentified residual patient CSF specimens were also tested for ergosterol.

RESULTS

Ergosterol remained stable in CSF at 4 °C and -80 °C. The mean variation and total error of the method were 7.4% and 15.8%, respectively. The method limit of quantification (LOQ) was 1.0 ng/mL, which translated to an in vitro LOQ of 2650 cells/mL or higher. A trace of ergosterol, below the LOQ, was detected in a patient specimen positive for cryptococcal meningitis but not in any other CSF specimens.

DISCUSSION: Ergosterol can be reliably detected in spiked human CSF samples and in the supernatant of N fowleri CSF cultures at concentrations of 1.0 to 500 ng/mL. The clinical utility of this method, however, requires further exploration.