PHMB at 0.1% inhibits bacterial growth but does not eradicate biofilm or protect against infection in a Tenebrio molitor model

Biofilm in chronic wound is an important public health problem in several countries due its delayed healing and ineffective local treatment. Several treatments are employed to inhibit bacterial growth, among which polyhexamethylene biguanide (PHMB) stands out. PHMB is widely known for its antibacterial properties through mechanisms that include the interaction of this compound with bacterial cell walls and DNA. However, there are conflicting data regarding its activity in eradicating mature biofilm. The purpose of this study was to investigate the in vitro and in vivo anti-biofilm activity of the PHMB as well as its toxicity. Herein, we show that PHMB inhibits the bacterial growth in all concentrations, except for Klebsiella pneumoniae. We used a well-established biofilm model to quantitatively assess the eradication of organisms. PHMB at 0,1% did not eradicate biofilms of Enterococcus faecalis, Klebsiella pneumoniae and Staphylococcus aureus. In vivo testing of PHMB in Tenebrio molitor larvae infected with Enterococcus faecalis, Klebsiella pneumoniae and Staphylococcus aureus, this compound did not induce any toxicity, however it increased AST levels by around 600%. Furthermore, the PHMB did not improves larvae survival and did not reduce bacterial load in their hemolymph. We suggest that PHMB in this concentration may represent an alternative to treatment of infection in wounds, but not as a therapeutic alternative for wounds with biofilm.