Antimicrobial Glycolipids: Evaluation of their Antimicrobial Activity, Antibiofilm Activity and Mechanisms of Action

• Autor(a) principal: Silva, Luna França Ferreira Pampim
• Data de Publicação: 2020
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositórios Científicos de Acesso Aberto de Portugal (RCAAP)
• Texto Completo: http://hdl.handle.net/10362/111052
• topic: medical device-associated infections; biofilm; rhamnolipids; sophorolipids; silicone; antimicrobial-functionalization; Domínio/Área Científica::Engenharia e Tecnologia::Engenharia Química

Biofilm formation by pathogenic agents on medical devices is a current issue and the available treatment seems ineffective in fighting these infections, therefore new effective molecules are in high demand. Biosurfactants are new promising compounds, that due to their structure can interact with cellular membrane of microorganisms, interfering with the microbial adhesion in the surface of medical devices to prevent these infections. The aim of this thesis was to evaluate the antimicrobial and antibiofilm activities and antimicrobial mechanism of biosynthesized mixtures of two glycolipids (i.e. rhamnolipids and sophorolipids). These two were immobilized in the surface of silicone by two methods, either by adsorption or covalent bond by plasma activation of the surface, to prevent microbial adhesion. Initially, antimicrobial activity was evaluated against different planktonic bacteria and S. aureus ATCC 25923, S. aureus ATCC 6538, clinic MRSA and S. epidermidis ATCC 28319 were the most vulnerable to the studied glycolipids mixtures. The mechanism of action of both glycolipids including membrane integrity (by propidium iodide uptake) and cellular viability (by resazurin reduction), cells’ surface hydrophobicity and cells’ surface charge modifications were studied. Rhamnolipids were the most active on disturbing membrane integrity, while sophorolipids were the most active on disturbing cellular viability. Both glycolipids increased cell surface hydrophobicity more effectively against S. aureus ATCC 25923, S. aureus ATCC 6538, MRSA and P. aeruginosa ATCC 15442, nevertheless rhamnolipids were more active. Furthermore, both compounds caused a decrease in cell surface charge, however only in a significant way against S. aureus ATCC 25923. Rhamnolipids adsorbed on the surface of silicone caused a decrease of the hydrophobicity of the material. Furthermore, using crystal violet assay and counting of colony forming units’ methods, it was verified that both glycolipids previously adsorbed on silicone caused a reduction in biofilm formation of sessile bacteria, most effectively against S. aureus ATCC 25923, S. aureus ATCC 6538 and MRSA. However, sophorolipids showed higher activity. Lastly, plasma treatment on silicone specimens functionalized with rhamnolipids provided good results, showing that this can be a good strategy to create a permanent functionalization to these surfaces. In conclusion, both glycolipids seem an optimistic approach in preventing biofilm formation on the surface of medical grade silicone, decreasing the risk for the development of these infections.