Essential oil-loaded polymeric film for antimicrobial application to a urinary catheter

Abstract

Catheter-associated urinary tract infections (CAUTIs) account for 80% of hospital-acquired infections worldwide. With these infections often being associated with the development of antimicrobial resistant infections, preventative strategies such as technological advances in medical devices and the use of alternative antimicrobials are seen as an emerging and rewarding field. The use of alternative antimicrobials such as essential oils has become an area of interest in amalgamating alternative therapeutics with medical devices to curb the observable resistance patterns. The aim of this study was to identify the most antimicrobially active essential oil, for encapsulation into Beta-cyclodextrin (βCD) biopolymer for development of a formulation intended to coat urinary catheters for the prevention of CAUTI development. The study design was carried out in three stages, antimicrobial screening, formulation, and validation of antimicrobial activity. In stage 1, a total of 26 essential oils were evaluated using the broth microdilution assay to obtain the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against 29 UTI causative pathogens. The MIC studies demonstrated that five (Cinnamomum zeylanicum, Santalum austrocaledonicum, Syzygium aromaticum, Thymus vulgaris, and Vetiveria zizanioides) of the 26 evaluated essential oils displayed noteworthy (≤1.00 mg/mL) broad-spectrum antimicrobial activity. The MBC assay showed that C. zeylanicum exhibited the best bactericidal activity at concentrations ≤1.00 mg/mL against 10 of the 29 pathogens tested. The antibiofilm assay evaluated the five most antimicrobially active essential oils against the five most prevalent biofilm-forming UTI causative pathogens (Escherichia coli, Enterococcus faecalis, Klebsiella pneumoniae, Proteus mirabilis, and Staphylococcus aureus). Results showed that C. zeylanicum inhibited biofilm formation of all five pathogens. This broad-spectrum biofilm inhibitory activity, coupled with the most broad-spectrum planktonic inhibitory and bactericidal activity, demonstrated that C. zeylanicum was the best essential oil to be taken forward into formulation. In stage 2, encapsulation of C. zeylanicum in βCD was carried out at five ratios of essential oil: βCD (5:95, 10:90, 11:80, 15:85, and 20:80) using the co-precipitation method. Thereafter physicochemical characterisation of the inclusion complex was carried out by Fourier-transform infrared spectroscopy (FTIR), Powder-X-Ray diffraction (PXRD), Zeta potential and size measurements, and thermogravimetric analysis (TGA). The percentage encapsulation was determined followed by antimicrobial evaluation of each inclusion complex. Characterisation (FTIR) verified the incorporation of the essential oil into βCD as evident, by shifts and increased intensities of characteristic βCD bands indicating that complexation had taken place. The highest encapsulation efficacy was exhibited at a ratio of 15:85 (Essential oil: βCD), whereas the best antimicrobial activity was observed for the 11:80 ratio. A crosslinked PVAbased film was formulated incorporating the 11:80 βCD complex and physicochemical and physico-mechanical properties were characterised. Thermal stability was seen well above the physiological temperature (37 °C). Swelling and degradation profiles indicated desirable characteristic with a low swelling ratio for 4% PVA (10.19), 4% PVA-βCD (7.98), and 4% PVA-CZ (7.68), and slow degradation was observed for the three films over 21-28 days. The final entrapment efficacy and encapsulation efficiency of C. zeylanicum in the 4% PVA-CZ film was 0.52 mg/mL and 29.71%, respectively. The in vitro release study of the C. zeylanicum loaded film and the C. zeylanicum inclusion complex were carried out in artificial urine and depicted as a slow release of C. zeylanicum from the film over a three-day period, with ~80.00% of the C. zeylanicum contents being released, relative to the 24-hour release from the inclusion complex with only ~44.00% C. zeylanicum released. In stage 3 the antimicrobial efficacy of the C. zeylanicum loaded film formulation was carried out and exhibited inhibition of growth of E. coli, E. faecalis, K. pneumoniae, P. mirabilis, and S. aureus over a 72-hour period in comparison to the control 4% PVA-βCD film tested without essential oil. The successful entrapment of C. zeylanicum essential oil and incorporation into a pharmaceutical formulation whilst retaining its antimicrobial activity serves as a proof of concept for the effective antimicrobial application on to a urinary catheter.