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- Liposomes as a nanoplatform to improve the delivery of antibiotics into Staphylococcus aureus biofilmsPublication . Ferreira, M.C.; Pinto, Sandra N.; Aires da Silva, Frederico; Bettencourt, Ana; Aguiar, Sandra I; Gaspar, Maria ManuelaABSTRACT - Staphylococcus aureus biofilm-associated infections are a major public health concern. Current therapies are hampered by reduced penetration of antibiotics through biofilm and low accumulation levels at infected sites, requiring prolonged usage. To overcome these, repurposing antibiotics in combination with nanotechnological platforms is one of the most appealing fast-track and costeffective approaches. In the present work, we assessed the potential therapeutic benefit of three antibiotics, vancomycin, levofloxacin and rifabutin (RFB), through their incorporation in liposomes. Free RFB displayed the utmost antibacterial effect with MIC and MBIC50 below 0.006 µg/mL towards a methicillin susceptible S. aureus (MSSA). RFB was selected for further in vitro studies and the influence of different lipid compositions on bacterial biofilm interactions was evaluated. Although positively charged RFB liposomes displayed the highest interaction with MSSA biofilms, RFB incorporated in negatively charged liposomes displayed lower MBIC50 values in comparison to the antibiotic in the free form. Preliminary safety assessment on all RFB formulations towards osteoblast and fibroblast cell lines demonstrated that a reduction on cell viability was only observed for the positively charged liposomes. Overall, negatively charged RFB liposomes are a promising approach against biofilm S. aureus infections and further in vivo studies should be performed.
- Antibiotic-lipid based nanosystem as a tool to specifically target Staphylococcus aureus biofilmsPublication . Ferreira, M.C. Magda Sofia Catroga Ferreira; Aguiar, Sandra Isabel Rodrigues de; Gaspar, Maria Manuela de Jesus Guilherme; Bettencourt, Ana Francisca de Campos SimãoAbstract - Hospital acquired infections (HAIs) is one of the leading causes of death worldwide, with Staphylococcus aureus being among the most prevalent microorganisms implicated in these infections. The ability of S. aureus to form biofilms and evade the immune system, along with the emergence of multidrug-resistant strains (MDR), exacerbates the complexity of eradicating infections. Conventional therapies characterized by prolonged antibiotic regiments have a poor rate of success, mainly due to the reduced penetration of antibiotics through the biofilms and low accumulation levels at infected sites. The ineffectiveness of current treatments has stimulated extensive research into the development of innovative therapeutic approaches. To address this need, the aim of this thesis was the development of a nanosystem by incorporating an antibiotic into liposomes, taking advantage of the unique benefits offered by these nanotechnological platforms. For this purpose, we first explored the antibacterial activity of three common antibiotics in clinical use – levofloxacin (LEV), vancomycin (VCM) and rifabutin (RFB) – against a reference strain of S. aureus (ATCC®25923™) in both planktonic and biofilm states. Subsequently, the antibiotics were incorporated into liposomes with different lipid compositions, and their incorporations parameters were assessed. Free RFB displayed the most potent antibacterial effect with MIC and MBIC50 below 0.006 µg/mL, along with the highest antibiotic loading capacity when nanoformulated, preserving its antibacterial activity. Based on these results, RFB was selected for further in vitro studies and the influence of the different lipid compositions on bacterial biofilm interactions was assessed, using a biofilm transwell model and confocal scanning laser microscopy analysis. It was observed that the positively charged RFB liposomes (LIP3) exhibited the highest interaction with biofilms. Nevertheless, RFB incorporated in negatively charged liposomes with fusogenic properties (LIP1) displayed lower MBIC50 values. Preliminary safety assessment of RFB formulations towards osteoblast and fibroblast cell lines indicated that a reduction in cell viability was only observed for the LIP3. Taking this into account, LIP1 was selected to move forward. Following these findings, the potential of free RFB was validated in a collection of S. aureus clinical isolates to provide a more accurate reflection of the challenges faced in real-world settings, in both planktonic (n=114) and biofilm (n=40) states. Additionally, the antibacterial activity of RFB incorporated in our developed liposome (LIP1) was validated against a set of clinical isolates (n=40) in both states. In conclusion, all the work developed contributed to the pursuit of effective therapeutic strategies for planktonic and biofilm-associated S. aureus infections, by exploring the potential of antibiotic repurposing and incorporating them into liposomes