Hyperbaric oxygen therapy counteracts biofilm micro-compartment phenomenon in murine thermal wounds.

Background: Biofilm antibiotic tolerance is partly explained by the behavior of a biofilm as an independent pharmacokinetic micro-compartment. Hyperbaric oxygen therapy has been shown to potentiate antibiotic effects in biofilms. The present study investigates the effect of hyperbaric oxygen therapy (HBOT) on the biofilm micro-pharmacokinetic/pharmacodynamic behavior of tobramycin in an animal biofilm model.

Methods: Full-thickness necroses were created mid-scapular on mice by means of a thermal lesion. After four days, three 16 h seaweed alginate biofilm beads containing PAO1 were inserted under the necrosis, and three beads were inserted under the adjacent non-affected skin. The mice were randomized to three groups I) HBOT for 1.5 h at 2.8 atm and 0.8 mg tobramycin/mouse subcutaneously; II) Tobramycin as monotherapy, same dose; III) Saline control group. Half the number of mice from group 1 and 2 were sacrificed, and beads were recovered after 3 h and the other half and the placebo mice were sacrificed and beads collected after 4.5 h.

Results: Lower CFUs were seen in the burned group receiving HBOT at 3 and 4.5 h compared to beads in the atmospheric environment (p = 0.043 and p = 0.0089). At 3 h, no CFU difference was observed in the non-burned skin (HBOT vs atmospheric). At 4.5 h, CFU in the non-burned skin had lower CFUs in the group receiving HBOT compared to the corresponding atmospheric group (p = 0.02). CFU was higher in the burned skin than in the non-burned skin at 3 h when HBOT was applied (p = 0.04), effect faded out at 4.5 h.At both time points, the tobramycin content in the beads under burned skin were higher in the HBOT group than in the atmospheric groups (p = 0.031 and p = 0.0078). Only at 4.5 h a higher tobramycin content was seen in the beads under the HBOT-treated burned skin than the beads under the corresponding non-burned skin (p = 0.006).

Conclusion: HBOT, as an anti-biofilm adjuvant treatment of chronic wounds, counteracts biofilm pharmacokinetic micro-compartmentalization through increased available tobramycin and augmented bacterial killing.