Pseudomonas aeruginosa may be isolated from skin wounds of burn patients, bedsore
and diabetic ulcers. The healing of wounds is often impaired by the intrinsic antibiotic
resistance, the tolerance to many antimicrobials and the ability to form biofilm of
this opportunistic pathogen. Finding new topical treatments to combine with antibiotics
is thus essential. Among natural products, the antimicrobial properties of honeys
have been known for millennia. In this study honey and visible light have been combined
to control the growth of P. aeruginosa PAO1. The irradiation by a broad spectrum light
source of bacteria inoculated onto 2 % w/v fir and forest honeydew (HD) honeys caused
a killing effect that the honeys alone or the light alone did not show. This antimicrobial
activity was light energy-dose and honey-concentration dependent. Among the tested
honeys, the fir and forest HD honeys were the most efficient ones. In particular,
the irradiation by blue LED (lambda(max) = 466 nm) yielded good rates of killing,
that were significantly higher in comparison to irradiation alone and honey alone.
Interestingly, a similar effect was obtained by plating bacteria on blue LED pre-irradiated
HD honeys. The combined use of honey and blue light was also successful in inhibiting
the biofilm formation of P. aeruginosa. The blue LED irradiation of PAO1 administered
with 10 % w/v forest HD honey significantly enhanced the inhibition of biofilm formation
in comparison to dark incubated honey.
