Fighting S. aureus catheter-related infections with sophorolipids: Electing an antiadhesive strategy or a release one?

Staphylococcus aureus medical devices related-infections, such as blood stream catheter are of major concern. Their prevention is compulsory and strategies, not prone to the development of resistance, to prevent S. aureus biofilms on catheter surfaces (e.g. silicone) are needed. In this work two different approaches using sophorolipids were studied to prevent S. aureus biofilm formation on medical grade silicone: i) an antiadhesive strategy through covalent bond of sophorolipids to the surface; ii) and a release strategy using isolated most active sophorolipids. Sophorolipids produced by Starmerella bombicola, were characterized by UHPLC-MS and RMN, purified by automatic flash chromatography and tested for their antimicrobial activity towards S. aureus. Highest antimicrobial activity was observed for C18:0 and C18:1 diacetylated lactonic sophorolipids showing a MIC of 50 µg mL-1. Surface modification with acidic or lactonic sophorolipids when evaluating the anti-adhesive or release strategy, respectively, was confirmed by contact angle, FTIR-ATR and AFM analysis. When using a mixture of acidic sophorolipids covalently bonded to silicone surface as antiadhesive strategy cytocompatible surfaces were obtained and a reduction of 90 % on biofilm formation was observed. Nevertheless, if a release strategy is adopted with purified lactonic sophorolipids a higher effect is achieved. Most promising compound was C18:1 diacateylated lactonic sophorolipid that showed no cellular viability reduction when a concentration of 1.5 mg mL-1 was selected and a reduction on biofilm around 5 log units. Results reinforce the applicability of these antimicrobial biosurfactants on preventing biofilms and disclose that their antimicrobial effect is imperative when comparing to their antiadhesive properties.

Seeking faster, alternative methods for glycolipid biosurfactant characterization and purification.

Biosurfactants have been investigated as potential alternatives for synthetic surfactants in several areas, for example, in environmental and pharmaceutical fields. In that regard, extensive research has been carried out with sophorolipids and rhamnolipids that also present various biological properties with therapeutic significance. These biosurfactants are obtained as complex mixtures of slightly different molecules, and thus when studying these microbial glycolipids, the ability to identify and purify the produced compounds is of extreme importance. This study aimed to develop improved methodologies for the identification, separation, and purification of sophorolipids and rhamnolipids. Therefore, an ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method was modified to ensure faster characterization of both sophorolipids and rhamnolipids, enabling the identification and fragmentation pattern description of 10 and 13 congeners, respectively. The separation and purification of these biosurfactants was achieved with novel reversed-phase solid-phase extraction methods guaranteeing the isolation of different glycolipids, including those considered for their significant biological activity (e.g. antimicrobial, anticancer). It was possible to isolate sophorolipids and rhamnolipids with purity of 94% and 99%, respectively. The methods presented herein can be easily implemented and are expected to make purification of these biosurfactants easier, facilitating the study of their individual properties in further works.