Ultrasound microbubbles enhance human β-defensin 3 against biofilms

The infection of orthopedic implantation devices with Staphylococcus has been a serious concern within the biomaterial community. Treatments are not always successful because of antibiotic-resistant bacteria biofilm infection. Recent studies have shown that combination of antibiotics with low-frequency ultrasound (US) can enhance the bactericidal activity effectively against the formation of biofilms in vitro pilot study. Meanwhile, microbubbles evolved as targeted drug-delivery agents can provide nuclei for inertial cavitation and lower the threshold for US-induced cavitation. Human β-defensin 3 (HBD-3) is a cationic antimicrobial peptide considered particularly promising for future bactericidal employment and has effect on antibiotic-resistant Staphylococcus biofilms. But the effect has not been reported when combined with US-targeted microbubble destruction (UTMD) in vivo.In this study, we evaluated the effect of HBD-3 combined with UTMD on two tested Staphylococcus by the spread plate method, crystal violet staining, confocal laser scanning microscopy, scanning electron microscopy, and real-time polymerase chain reaction.In the study, we found that the biofilm densities, the percentage of live cells, and the viable counts of two tested Staphylococcus that recovered from the biofilm on the titanium surface in mice were significantly decreased in the group of the HBD-3 combined with UTMD, compared with those of other groups. Furthermore, in the experiment, we found out that UTMD could enhance HBD-3 activity, which inhibits the biofilm-associated genes expression of icaAD and the methicillin-resistance genes expression of MecA by promoting the icaR expression simultaneously.The combination of HBD-3 with UTMD can play a significant role on the elimination of the antibiotic-resistant Staphylococcus biofilms in vivo.