Multiplexed MALDI fingerprints for rapid detection of spontaneous bacterial peritonitis.

Background: The efficient diagnosis of spontaneous bacterial peritonitis (SBP) has been hindered by the low sensitivity of current clinical indicators. A rapid and accurate detection method for SBP is essential to enable early diagnosis and prompt intervention.

Methods: Given the critical role of specialized metabolites in bacterial infections, we combined matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) with partial least squares discriminant analysis (PLS-DA) to directly analyze intact protein and specialized lipid fingerprints in ascitic fluid, in order to effectively distinguish spontaneous bacterial peritonitis (SBP) from noninfected ascites.

Results: MALDI-TOF MS delivers results in minutes to hours, far surpassing traditional culture-based methods that take 24-48 hours. Its capacity for rapid, direct pathogen detection in ascitic fluid is critical for prompt treatment and precise antibiotic selection. Unlike database-dependent approaches, PLS-DA serves as an independent statistical tool for SBP classification. MALDI-TOF MS enables direct analysis of lipid species (500-1000 Da) and intact proteins (2000-20,000 Da) without bacterial culture. Notably, α-defensins, particularly human neutrophil peptides (HNP-1, HNP-2), emerged as promising SBP biomarkers, while a novel peptide-SSSYSKQFTSSTSYNRGDSTFES (a fibrinogen fragment)-was associated with noninfected ascites. The combination of HNP-2 (P-3368) and this peptide (P-2550) achieved an AUC of 0.956, demonstrating outstanding diagnostic accuracy for SBP.

Conclusions: MALDI-TOF MS advances SBP diagnosis by enabling the multiplexed detection of diverse lipids and proteins, offering crucial insights into the metabolic interplay of the host's response to infection.