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Introduction: Quaternary ammonium salts (QASs) are widely spread cationic surfactants applicable in various industrial branches. QASs manifesting antibacterial effect contain hydrophilic core and a long alkyl chain in the structure. These compounds have strong antimicrobial activity against certain bacteria strains especially non-spore forming, yeasts, or protozoa. S. Aureus is a frequent cause of nosocomial infections and plays an important role in the persistence of chronic infections, especially when it’s attached to medical implants and host tissue, and developed in mature biofilm. Either way, this pathogen represents a significant burden on the healthcare system and new antimicrobial compounds are always required in clinical practice. Hypothesis and aims: Our main research activity involves the synthesis of novel compounds based on QASs and evaluating their eradication ability against pathogenic S. Aureus in biofilm and free-floating form and subsequent effectivity comparison against these two different bacterial states. Methodology: All newly prepared compounds were prepared by the nucleophilic reaction, verified by Nuclear Magnetic Resonance (NMR) and High-Resolution Mass Spectrometry (HR-MS). The antimicrobial properties were evaluated by microdilution broth assay and by Calgary device based assay with MIC, MBC, and MBEC as outcomes. Results: Series of novel QAS were prepared and verified. The MICs, MBCs, and MBECs were measured for all substances and have shown antimicrobial potential against S. Aureus in both states, however higher concentration was needed for biofilm eradication. The activities of newly prepared compounds were comparable to QASs based disinfections already known and commonly used in practice. Conclusion: Series of synthesized compounds underwent antimicrobial evaluation and several compounds have shown antimicrobial potential against S. Aureus in planktonic and biofilm form.

Introduction: An increasing microbial resistance to known antibiotics raises the demand for new antimicrobials. New antibacterial agent should have a good activity against planktonic as well as biofilm bacteria. Quaternary ammonium compounds (QACs), are widely used in medicine, have proven antimicrobial properties, and are low toxic and low irritating. In this study new QACs were evaluated for their biofilm eradication efficiency as antibacterial compounds and as irrigants in combination with Er:YAG photoacoustic streaming. Aims: To evaluate the effectiveness of new QACs against E. faecalis biofilms and to increase the effectiveness of QACs with laser treatment. Method: The biofilm of E. faecalis were grown on titanium surface. The fraction of the dead cells and the biofilm surface coverage was determined with LIVE/DEADTM using confocal microscopy (CLSM) before and after QACs treatment. To enhance to effectiveness the biofilm samples were pretreated with QACs followed by short laser Er:YAG photoacoustic streaming treatment. Results: All tested QACs were effective against the E. faecalis biofilms. The best anti-biofilm compounds were N-Alkylimidazolinium derivatives. Compared to planktonic bacteria the bacteria in the biofilm were up to 10 fold more resistant. The fraction of the dead bacteria that were treated with QACs followed by Er:YAG photoacoustic streaming increased significantly compared to the chemical treatment alone. In addition, the biofilm surface coverage decreased after laser treatment. Conclusions: The results suggest that new QACs have a great potential as antibacterial compounds effective against biofilms of E. faecalis. The laser treatment can significantly improve the effectiveness of QACs treatment.