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Surface functionalization-dependent localization and affinity of SiO2 nanoparticles within the biofilm EPS matrix

2020-12, Hiebner, Dishon W., Barros, Caio H. N., Quinn, Laura, Vitale, Stefania, Casey, Eoin

The contribution of the biofilm extracellular polymeric substance (EPS) matrix to reduced antimicrobial sus-ceptibility in biofilms is widely recognised. As such, the direct targeting of the EPS matrix is a promising biofilmcontrol strategy that allows for the disruption of the matrix, thereby allowing a subsequent increase in suscep-tibility to antimicrobial agents. To this end, surface-functionalized nanoparticles (NPs) have received considerableattention. However, the fundamental understanding of the interactions occurring between engineered NPs andthe biofilm EPS matrix has not yet been fully elucidated. An insight into the underlying mechanisms involvedwhen a NP interacts with the EPS matrix will aid in the design of more efficient NPs for biofilm control. Here wedemonstrate the use of highly specificfluorescent probes in confocal laser scanning microscopy (CLSM) toillustrate the distribution of EPS macromolecules within the biofilm. Thereafter, a three-dimensional (3D)colocalization analysis was used to assess the affinity of differently functionalized silica NPs (SiNPs) and EPSmacromolecules fromPseudomonasfluorescensbiofilms. Results show that both the charge and surface functionalgroups of SiNPs dramatically affected the extent to which SiNPs interacted and localized with EPS macromole-cules, including proteins, polysaccharides and DNA. Hypotheses are also presented about the possible physico-chemical interactions which may be dominant in EPS matrix-NP interactions. This research not only develops aninnovative CLSM-based methodology for elucidating biofilm-nanoparticle interactions but also provides a plat-form on which to build more efficient NP systems for biofilm control.

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Tailoring Nanoparticle-Biofilm Interactions to Increase the Efficacy of Antimicrobial Agents Against Staphylococcus aureus

2020-07-07, Fulaz, Stephanie, Devlin, Henry, Vitale, Stefania, Quinn, Laura, O'Gara, James P., Casey, Eoin

Background: Considering the timeline required for the development of novel antimicrobial drugs, increased attention should be given to repurposing old drugs and improving anti-microbial efficacy, particularly for chronic infections associated with biofilms. Methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA) are common causes of biofilm-associated infections but produce different biofilm matrices.MSSA biofilm cells are typically embedded in an extracellular polysaccharide matrix, whereas MRSA biofilms comprise predominantly of surface proteins and extracellular DNA (eDNA). Nanoparticles (NPs) have the potential to enhance the delivery of antimicro-bial agents into biofilms. However, the mechanisms which influence the interactions between NPs and the biofilm matrix are not yet fully understood. Methods:To investigate the influence of NPs surface chemistry on vancomycin (VAN) encapsulation and NP entrapment in MRSA and MSSA biofilms, mesoporous silica nano-particles (MSNs) with different surface functionalization (bare-B, amine-D, carboxyl-C,aromatic-A) were synthesised using an adapted Stöber method. The antibacterial efficacy of VAN-loaded MSNs was assessed against MRSA and MSSA biofilms. Results: The two negatively charged MSNs (MSN-B and MSN-C) showed a higher VAN loading in comparison to the positively charged MSNs (MSN-D and MSN-A). Cellular binding with MSN suspensions (0.25 mg mL−1) correlated with the reduced viability of both MSSA andMRSA biofilm cells. This allowed the administration of low MSNs concentrations while maintaining a high local concentration of the antibiotic surrounding the bacterial cells. Conclusion: Our data suggest that by tailoring the surface functionalization of MSNs,enhanced bacterial cell targeting can be achieved, leading to a novel treatment strategy for biofilm infections.