Background

In recent years, the frequency of Candida infections caused by both nosocomial and opportunistic Candida strains has increased rapidly especially due to the growing number of transplant recipients, cancer patients and patients who receive immunosuppressive therapy (Sanguinetti et al., 2015). Apart from this, development of candidemia in patients with implanted biomaterials such as catheters (Simitsopoulou et al., 2014), dental implants (Li et al., 2012), voice prostheses (Talpaert et al., 2015) and prosthetic devices (Ramage et al., 2006) causes an urgency to develop preventive strategies such as antimicrobial coatings in the management of recalcitrant Candida infections (Ramage et al., 2006). Since biofilm formation plays a pivotal role in the development of recalcitrant candidemia (Simitsopoulou et al., 2014), not only antimicrobial therapies, but also antibiofilm strategies are needed for the prevention of biomaterial-associated Candida infections. Recently, a growing increase in the incidence of candidemia has been associated with the increase in biofilm formation and resistance to antifungal therapy (Francisconi et al., 2020). Substances obtained from traditional medicinal plants, such as volatile essential oils have been regarded as attractive sources for new antimicrobials(Francisconi et al., 2020). Essential oils, originating from different parts of a variety of aromatic plants not only have antimicrobial but also have antibiofilm effects against various microorganisms (Akthar et al., 2014; Kim et al., 2016; Sahal et al., 2019 and 2020). Therefore, the antibiofilm effects of several essential oils against different Candida species have been studied for years (Almeida et al., 2016; Kryvtsova et al., 2019). Recently, essential oils have also been evaluated as agents that prevent biomaterial-associated Candida infections. In particular, there is a growing interest in the use of a lemongrass essential oil as a coating agent (Sahal et al., 2019 and 2020). Often high costs and complicated technologies are used for both applying the coating and determination of the antibiofilm effects. For example, Liakos et al. (2017) used electrospinning to apply a cellulose acetate based coating containing the essential oil and Anghel et al. (2012) used Confocal Laser Scanning Microscopy images to asses fungal biofilm architecture on Fe₃O₄/C₁₈/essential oil coated Provox^TM voice prostheses. These techniques are often very expensive, laborious and require highly qualified equipment and personnel. Thus, they constrain an ease and rapid screening of essential oils. Therefore, we aimed to develop cheap, effective and easily applicable protocols to rapidly screen the anti-candida biofilm effects of various essential oils coated on silicone rubber.

In the first part, we describe the preparation of essential oil coated silicone rubber surface using a hypromellose ointment/essential oil mixture. In this part, hypromellose ointment was used as a vehicle because it mixes well with essential oils and because of its good adhesive properties to wetted surfaces. In the second part, we describe the determination of the biofilm mass of Candida biofilm on these surfaces using a modified crystal violet binding assay. Both protocols can be applied easily and rapidly with simple and accessible equipment.