Vancomycin-decorated microbubbles as a theranostic agent for Staphylococcus aureus biofilms

Theranostic Microbubbles with Homogeneous Ligand Distribution for Higher Binding Efficacy

“…A study on P-selectin-targeted microbubbles reported that microbubble dissociation or detachment under flow was related to the receptor density on the target surface [62], with our results corresponding to the dissociation rate of the highest receptor density tested (109 molecules/µm 2 ). In our study, the percentage of microbubbles remaining bound at increasing shear stress was several times higher than the percentage reported recently on vancomycin-decorated microbubbles binding to a bacterial biofilm under flow [20]. With the experimental set-up used for the present study, the unbound targeted microbubbles kept on circulating through the µ-slide with the HUVEC monolayer for as long as the flow was on.…”

“…Then, flow was started at a shear stress of 7.5 dyn/cm 2 and a mixture of 1.36 µL Hoechst 33342 (10 mg/mL) and 10.9 µL CellMask™ Green Plasma Membrane Stain (5 mg/mL) in 200 µL EGM-2 was injected into the upstream Luer injection port with a 1 mL Luer Solo syringe (Omnifix-F, B Braun, Melsungen, Germany) and 19G needle (Sterican, B Braun). The fluorescent dyes were allowed to incubate under flow for 15 min, after which the µ-slide was inverted to have the HUVEC monolayer on the top side of the µ-slide [20]. For the binding efficacy under flow experiments, different flow conditions were evaluated with a shear stress of 1.25, 2.22, 4.45, 5.0, 6.8, or 7.5 dyn/cm 2 .…”

“…Furthermore, phospholipid-coated microbubbles can be functionalized with the addition of a ligand targeted to a specific biomarker [15,16]. Targeted microbubbles can be used for ultrasound molecular imaging [17][18][19], and when combined with therapeutic agents they function as theranostic agents [20][21][22]. A recent review on targeted microbubbles stated that when comparing the therapeutic effects of targeted and non-targeted microbubbles, treatment with targeted microbubbles always resulted in a significantly better therapeutic outcome [23].…”

Dispersing and Sonoporating Biofilm-Associated Bacteria with Sonobactericide

“…On the other hand, enhanced microbubble displacement may result in less cell death, as reported in endothelial cells, where non-displacing microbubbles were more lethal [14]; although, it should be noted, again, that mammalian cells and S. aureus are very different cell types. To further understand the relationship between microbubble displacement and bacterial cell death and dispersion, a similar study, such as that of van Rooij et al [14], could be conducted using non-targeted and targeted microbubbles for bacterial biofilms, such as with the innovative, recently published targeted microbubbles using vancomycin [17] or Affimer protein [25]. Bacterial dispersal was a direct consequence of microbubble displacement and subsequent clustering, quantitatively supported in Figure 8, which was possibly due to secondary Bjerknes forces.…”

“…Sonobactericide has been demonstrated in several papers on Staphylococcus aureus (S. aureus) biofilms [17][18][19][20][21][22][23][24][25], which is the predominate infecting microbe for many types of infections, and it is associated with more severe disease, higher mortality, and longer hospital stays [26]. A range of effects, as a result of sonobactericide on S. aureus using non-targeted microbubbles, have been observed or suggested, including biofilm disruption/dispersal [19,21], sonoporation (not quantified) [23], and enhanced antimicrobial efficacy [19,21,23,24].…”