Aims Biofilms are ubiquitous and when mature have a complex structure of microcolonies in an extracellular polysaccharide and extracellular DNA matrix. Indwelling medical devices harbour biofilms which have been shown to cause infections and act as reservoirs for pathogens. Urinary catheters are often in place for considerable periods of time and are susceptible to both encrustation and biofilm formation. Strategies for minimising biofilm occurrence underpin an active research area in biomedicine. Manuka honey has, inter alia, well-established antibacterial properties. This study aims to assess the influence of honey on early biofilm formation in an established in vitro model.
Methods An established model of early biofilm formation using static bacterial cultures in vinyl 96-well plates was used to grow Escherichia coli, strain ATC 25922 and Proteus mirabilis, strain 7002. Planktonic cells were removed and the residual biofilm was stained with crystal violet, which were subsequently eluted and quantified spectrophotometrically. Manuka honey (Unique Manuka Factor 15+) was added either with the bacteria or up to 72 hours after.
Results Biofilms in this model was developed over 3 days, after which growth stalled. Mixed (1:1) cultures of E. coli and P. mirabilis grew slower than monocultures. In mixed cultures, honey gave a dose-dependent reduction in biofilm formation (between 3.3 and 16.7%w/v). At 72 hours, all concentrations inhibited maximally (p<0.001). Application of honey to cultures after 24 and 48 hours also reduced the adherent bacterial biomass (p<0.05–p<0.01).
Conclusion Manuka honey at dilutions as low as 3.3% w/v in some protocols and at 10% or above in all protocols tested significantly inhibits bacterial attachment to a vinyl substrate and reduces further early biofilm development. No augmentation of growth over untreated controls was observed in any experiment.
- ANTIMICROBIAL RESISTANCE
- BIOLOGICAL SCIENCES
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Handling editor Slade Jensen
Contributors SE made a substantial contribution to the design, organisation and conduct of the study (including acquisition of study data). AJC and BAL made a substantial contribution to the conception, design, organisation and conduct of the study. SF made a substantial contribution to the organisation and conduct of the study. BRB critiqued the output for important intellectual content.
Funding The study was funded internally.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement The work described here forms part of a continuum in which there is collaboration between the Departments of Microbiology and Biomedical Science at the University of Portsmouth and the Faculty of Health Sciences at the University of Southampton. The science available for sharing includes experience of growing organisms on a variety of substrates and alternative methods of quantifying biofilm growth. In particular, we have as yet unpublished studies on growing mature biofilms on membranes with continuous flow of medium. For information, contact firstname.lastname@example.org or email@example.com