Differences in the Profile of Aromatic Metabolites in the Corresponding Blood Serum and Cerebrospinal Fluid Samples of Patients with Secondary Bacterial Meningitis

<b>Background:</b> Secondary (nosocomial) bacterial meningitis remains a serious problem in patients with severe brain damage. The aim of this study was to assess the differences in the aromatic metabolites of tryptophan, phenylalanine, and tyrosine, in serum and cerebrospinal fluid (CSF) samples collected simultaneously from patients with long-term sequelae of severe brain damage with suspected secondary bacterial meningitis. <b>Methods:</b> Group I included 16 paired serum and CSF samples from patients (<i>N</i> = 11) without secondary bacterial meningitis; group II included 13 paired serum and CSF samples from patients (<i>N</i> = 4) with secondary bacterial meningitis. <b>Results:</b> The median concentrations of serum 5-hydroxyindole-3-acetic, CSF 4-hydroxyphenyllactic (<i>p</i>-HPhLA), CSF 4-hydroxyphenylacetic, CSF phenyllactic, and indole-3-lactic acids in serum and CSF were statistically higher in group II compared to group I (<i>p</i>-value ≤ 0.03), while 4-hydroxyphenylpropionic and indole-3-acetic in serum were lower in group II compared to group I (<i>p</i>-value = 0.04). In group I, <i>p</i>-HPhLA serum concentrations were greater than or equal to its CSF concentrations in 14 paired samples; in group II, <i>p</i>-HPhLA concentrations in serum were lower than in CSF in all paired samples. <b>Conclusions:</b> The obtained results demonstrate the differences in the profile of aromatic metabolites in serum and CSF and may confirm the hypothesis of the <i>p</i>-HPhLA microbial origin in the CSF of patients with secondary bacterial meningitis.