Pseudomonas aeruginosa contributes to many chronic infections and has been found to be resistant to multiple antibiotics. Pseudomonas use a quorum sensing system (QS) to control biofilm establishment and virulence factors, and, thus, quorum sensing inhibitors (QSIs), such as meta-bromo-thiolactone (mBTL), are promising anti-infective agents. Accordingly, this study intended to investigate the antibacterial and anti-virulence activity of mBTL-loaded calcium alginate nanoparticles (CANPs) against Pseudomonas aeruginosa and different QS mutants. The results show that the mBTL-CANPs had higher antibacterial activity, which was made evident by decreases in all tested strains except the ∆lasR/∆rhlR double mutant, with MIC₅₀ (0.5 mg/mL) of mBTL-CANPs compared with free mBTL at MIC₅₀ (˃1 mg/mL). The biofilm formation of P. aeruginosa and some QS-deficient mutants were reduced in response to 0.5–0.125 mg/mL of mBTL-encapsulating CANPs. The pyocyanin production of the tested strains except ∆lasA and ∆rhlR decreased when challenged with 0.5 mg/mL of mBTL-loaded NPs. The subsequent characterization of the cytotoxic effect of these NPs on human lung epithelial cells (A549) and cystic fibrosis fibroblast cells (LL 29) demonstrated that synthesized NPs were cytocompatible at MIC₅₀ in both cell lines and markedly reduced the cytotoxic effect observed with mBTL alone on these cells. The resulting formulation reduced the P. aeruginosa strains’ adhesion to A549 comparably with mBTL, suggesting their potential anti-adhesive effect. Given the virulence suppressing action, cytocompatibility, and enhanced anti-biofilm effect of mBTL-CANPs, and the advantage of alginate-based NPs as an antimicrobial delivery system these nanoparticles have great potential in the prophylaxis and treatment of infection caused by Pseudomonas aeruginosa.

Quorum-sensing inhibitors have recently garnered great interest, as they reduce bacterial virulence, lower the probability of resistance, and inhibit infections. In this work, meta-bromo-thiolactone (mBTL), a potent quorum and virulence inhibitor of Staphylococcus aureus (S. aureus) and methicillin-resistant S. aureus (MRSA), was formulated in chitosan nanoparticles (ChNPs) using the ionic gelation method. The mBTL-loaded-ChNPs were characterized by their particle size, polydispersity index, zeta potential, morphology, and drug release profile. The results show that the mBTL-loaded-CNPs comprised homogenized, spherical nanoparticles ranging from 158 ± 1.3 to 284 ± 5.6 nm with a sustainable release profile over 48 h at 37 °C. These findings confirm the successful preparation of mBTL-loaded-ChNPs. Confocal laser scanning microscopy showed a significant reduction in the number of viable cells, indicating the antibacterial efficacy of mBTL. Biofilms were observed by scanning electron microscopy, which showed that the bacterial cells in the control experiment were enclosed in thick biofilms. In the presence of mBTL, the bacterial cells remained disordered and did not form a biofilm. mBTL-loaded-ChNPs represent a potential approach to overcoming antimicrobial resistance in the treatment of MRSA infection.

Of late, the focus has been shifted towards quorum sensing inhibitors which reduce bacterial virulence and lower the probability of resistance and refining infections. In this work, meta-bromo-thiolactone (mBTL), a potent quorum and virulence inhibitor against Staphylococcus aureus and MRSA phenotypes, was formulated in chitosan nanoparticles (ChNPs) using ionic gelation method. mBTL-loaded-ChNPs were characterized for particle size, polydispersity index, zeta potential. Morphology was visualized by Transmission Electron Microscopy (TEM), drug release profile and antibiofilm analysis using Confocal Laser Scanning Microscope (CLSM) and Scanning Electron Microscopy (SEM) were performed. Synthesized mBTL-loaded-CNPs showed homogenized nano-size particles ranging from 158+1.3 to 284+5.6 nm with spherical particles that exhibited sustainable release profile over 48 hr at 37 °C. These findings revealed successful preparation of mBTL-loaded-ChNPs, that further showed effective antibiofilm activity at MIC50 (0.5 mg/mL) where all strains displayed reduced biofilm formation compared to untreated strains. CLSM results showed a significant reduction in the number of viable cells, indicating the effectiveness of m-BTL as an antibacterial agent. SEM analysis permitted visualization of biofilm structure in relation to the spatial localization of important biofilm matrix components, the formed biofilms were clearly distinguished in the SEM images. Bacterial cells in the control group were enclosed in thick biofilms. In contrast, there was a considerable reduction in biofilm production when mBTL was present, where bacterial cells seemed less ordered and more scattered with no detectable biofilms. In conclusion, mBTL-loaded-ChNPs is a potential alternative treatment to overcome antimicrobial resistance and condensed MRSA infections.