Abstract
Objectives: In adult ventricular assist device (VAD) programs in Australian hospitals, Medihoney Antibacterial Wound Gel (MAWG) is routinely used at the skin exit-site of VAD drivelines to prevent infections; however, its effectiveness remains unclear. Our aim was to assess antimicrobial activity of Medihoney wound gel, using in vitro models that mimic clinical biofilms grown at the driveline exit-site.Methods: Antimicrobial susceptibility testing of MAWG was performed for 24 clinical isolates grown under planktonic conditions, and four representative strains grown as biofilms. Different antimicrobial mechanisms of MAWG were assessed respectively for their relative contribution to its anti-biofilm activity. A colony biofilm assay and a drip-flow biofilm reactor assay mimicking the driveline exit-site environment were used to evaluate the activity of MAWG against biofilm growth at the driveline exit-site.Results: MAWG demonstrated species-specific activity against planktonic cultures [minimum inhibitory concentrations (MICs), 5–20% weight/volume (W/V) for Staphylococcus species, 20–>40% (W/V) for Pseudomonas aeruginosa and Candida species]. Higher concentrations [MICs, 30–>80% (W/V)] were able to inhibit biofilm growth, but failed to eradicate pre-established biofilms. The anti-biofilm properties of MAWG were multi-faceted, with the often-advertised “active” ingredient methylglyoxal (MGO) playing a less important role. The colony biofilm assay and the drip-flow biofilm reactor assay suggested that MAWG was unable to kill biofilms pre-established in a driveline exit-site environment, or effectively prevent planktonic cells from forming adherent monolayers and further developing mature biofilms.Conclusion: Our work suggests a suboptimal effectiveness of MAWG in preventing driveline infections due to biofilm development.
Highlights
Medical-grade honeys have been used for the treatment of infection in chronic wounds and persistent diabetic ulcers (Soffer, 1976; Dunwoody and Acton, 2008)
Medihoney Antibacterial Wound Gel (MAWG) at concentrations of 30, 50, >80, and 30% (W/V) were needed to inhibit biofilm growth by 50% for S. aureus, S. epidermidis, P. aeruginosa, and C. albicans, respectively (Table 2, see BMIC50)
MAWG at the highest concentration used in this study [80% (W/V)], was unable to fully eradicate mature biofilms pre-formed by any of these microorganisms (Table 2, see Minimum biofilm eradication concentration (MBEC))
Summary
Medical-grade honeys have been used for the treatment of infection in chronic wounds and persistent diabetic ulcers (Soffer, 1976; Dunwoody and Acton, 2008). They have been used for prophylactic indications such as prevention of peritoneal dialysis catheter exit-site infection (Forbes et al, 2016). The discrepancy between the in vitro efficacy of Manuka-type honey and in vivo efficacy of MAWG against biofilms may be partially due to the use of over-simplified microplate-based biofilm assays by many other in vitro studies (Cooper et al, 2014; Hammond et al, 2014; Lu et al, 2019). Microplate-based biofilm assays often neglect the impact of the clinical environment and might not adequately reflect infections at the unique skin exit-site of percutaneous medical devices (Buhmann et al, 2016)
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