Concentrations of manuka honey equivalent to the MIC for
planktonically grown cells were able to prevent biofilm
development; manuka honey applied at just 5 % less than
the MBC for planktonically grown cells resulted in an almost
complete abrogation of biofilm development. In both cases,
there was undoubtedly some degree of growth inhibition as
observed from the growth studies. However, the large
reduction in biofilm biomass using the MIC did not support
the small reduction in growth using the same concentration
of manuka honey, suggesting that the loss of biofilm biomass
was the consequence of more than growth inhibition alone.
Treatment of established biofilms of S. pyogenes with
manuka honey also facilitated a reduction in biofilm
biomass. Since these biofilms had been grown for 24 h
prior to treatment, the observed reduction in biomass was
likely the result of cell death, which was verified by Live–
Dead viability staining which showed that non-viable cells
were present in both developing and established biofilms
that were treated with manuka honey. It was possible that
the reduced TVCs could have been the result of a proportion
of the population being in a viable but non-culturable state,
which often occurs in response to cellular stress. This would
have meant that the reduction in TVC observed might not
have been attributed solely to cell death. However, the
viability staining showing the presence of non-viable cells
suggested that this was unlikely to be the case.