Introduction: Some metabolites of aromatic amino acids are known to be of microbial origin [https://doi.org/10.1038/nature24661]. Elevated concentrations of microbial 4-hydroxyphenyllactic acid (p-HPhLA) in cerebrospinal fluid (CSF) have previously been detected in post-neurosurgical patients with signs of secondary bacterial meningitis in comparison to those without signs of secondary bacterial meningitis [https://doi.org/10.3390/jpm12030399].

Objectives: To assess the ratio of p-HPhLA in serum and CSF samples collected simultaneously from patients with long-term sequelae of severe brain damage with suspected secondary bacterial meningitis.

Methods: Blood (n=29) and CSF (n=29) samples were collected simultaneously within one day from patients (n=15) with long-term sequelae of severe brain damage with suspected secondary bacterial meningitis. Group I included 16 paired serum and CSF samples from patients without secondary bacterial meningitis (n=11, 8 men, 3 women, aged from 21 to 82); group II included 13 paired serum and CSF samples from patients with secondary bacterial meningitis (n=4, 2 men, 2 women, aged from 22 to 65). p-HPhLA concentrations were detected using HPLC-MS/MS.

Results: Median p-HPhLA concentrations in serum: group I—975 nmol/l; group II—1676 nmol/l; Mann-Whitney U-test, p-value, - 0.008. Median p-HPhLA concentrations in CSF: group I—414 nmol/l; group II—2578 nmol/l; Mann-Whitney U-test, p-value, < 0.001. In group I, p-HPhLA concentrations in serum were higher than those in CSF in 13 of 16 samples; in group II, p-HPhLA concentrations in serum were lower than those in CSF in all samples.

Conclusion: The obtained results may confirm the hypothesis of the microbial origin of p-HPhLA in CSF in patients with secondary bacterial meningitis.