Quorum Sensing as a Potential Biomarker Target to Diagnose Staphylococcus aureus Infections

[eng] Staphylococcus aureus is a Gram-positive bacterium capable of causing a wide range of infections, from minor skin conditions to severe diseases like pneumonia and sepsis. Its adaptability, virulence factors, and the emergence of multidrug-resistant strains, such as methicillin-resistant S. aureus (MRSA), pose significant global health challenges. Current diagnostic methods, such as culture-based techniques, are time-consuming, delaying treatment and contributing to antimicrobial resistance. This research focuses on developing immunochemical diagnostic tools to detect S. aureus infections rapidly and effectively. The work targets the main quorum sensing (QS) system of this bacterium, known as the accessory gene regulator (agr) system, which coordinates the production of virulence factors through autoinducing peptides (AIPs). AIPs are presented as biomarkers for detecting infections, phenotyping strains based on their agr group, and guiding therapeutic strategies. To achieve these goals, monoclonal and polyclonal antibodies against AIPs were developed and implemented in ELISAs. These assays demonstrated exceptional sensitivity, with low IC50 values (20.41 nM for AIP1o; 2.70 nM for AIP2o; 6.54 nM for AIP3c; and 2.19 nM for AIP3o), exceeding traditional detection methods like mass spectrometry. Additionally, the ELISAs were successfully adapted for detecting AIPs in bacterial culture media, providing rapid results within 2–3 hours. The study also addressed the challenges of analyzing AIPs in complex biological samples like bronchial aspirates (BAS). Various sample preparation strategies, including enzymatic treatments and immunoaffinity purification techniques, were evaluated. Immunoaffinity spin columns (ISCs) emerged as a scalable and robust method for AIP purification, enabling accurate detection in clinical respiratory samples. This work represents a significant advancement in diagnostic technology for S. aureus, offering rapid, sensitive, and clinically relevant tools. Further research is needed to validate these methods and expand their application, but they hold great promise for improving patient outcomes and combating antimicrobial resistance.