Surface-Adaptive, Antimicrobially Loaded, Micellar Nanocarriers with Enhanced Penetration and Killing Efficiency in Staphylococcal Biofilms

Abstract

Biofilms cause persistent bacterial infections and are extremely recalcitrant to antimicrobials, due in part to reduced penetration of antimicrobials into biofilms that allows bacteria residing in the depth of a biofilm to survive antimicrobial treatment. Here, we describe the preparation of surface-adaptive, Triclosan-loaded micellar nanocarriers showing (1) enhanced biofilm penetration and accumulation, (2) electrostatic targeting at acidic pH toward negatively charged bacterial cell surfaces in a biofilm, and (3) antimicrobial release due to degradation of the micelle core by bacterial lipases. First, it was established that mixed-shell-polymeric-micelles (MSPM) consisting of a hydrophilic poly(ethylene glycol) (PEG)-shell and pH-responsive poly(β-amino ester) become positively charged at pH 5.0, while being negatively charged at physiological pH. This is opposite to single-shell-polymeric-micelles (SSPM) possessing only a PEG-shell and remaining negatively charged at pH 5.0. The stealth properties of the PEG-shell combined with its surface-adaptive charge allow MSPMs to penetrate and accumulate in staphylococcal biofilms, as demonstrated for fluorescent Nile red loaded micelles using confocal-laser-scanning-microscopy. SSPMs, not adapting a positive charge at pH 5.0, could not be demonstrated to penetrate and accumulate in a biofilm. Once micellar nanocarriers are bound to a staphylococcal cell surface, bacterial enzymes degrade the MSPM core to release its antimicrobial content and kill bacteria over the depth of a biofilm. This constitutes a highly effective pathway to control blood-accessible staphylococcal biofilms using antimicrobials, bypassing biofilm recalcitrance to antimicrobial penetration.

Targeting microbial biofilms: current and prospective therapeutic strategies

“…Stimuli-triggered mechanisms by nanoparticles can also enhance the selectivity of drug activation or delivery to cells within a biofilm, protecting host tissues and the commensal microbiota while targeting infective agents within pathological microniches 143,145,146 . Delivery of the antibacterial agent farnesol via acidic pH-triggered polymeric nanoparticles enhanced its biofilm-targeting activity 4-fold (compared to farnesol alone); thus, the delivery system greatly improved the drug efficacy against an oral biofilm infection in vivo following topical treatment 146 .…”

“…These water-soluble polymeric nanocarriers can encapsulate hydrophobic and apolar drugs into aqueous solution, which is a crucial issue in product development. Similarly, nanoparticles that are conjugated with a pH-responsive element 145 or pH-sensitive surface charge switching 147 were developed to increase biofilm penetration and selective bacterial binding for targeted delivery and antibacterial activity in acidic conditions.…”

Recent Advances and Future Prospects on Adaptive Biomaterials for Antimicrobial Applications

“…Besides acidity, infection sites are often enriched with bacterial metabolic enzymes and virulence factors. For instance, β‐galactosidases, alkaline phosphatases (ALPs), nitroreductases, proteinases, lipases, phospholipases, toxins, and hyaluronidases may exhibit specifically at the infection sites and are crucial for the bacterial metabolism and survival inside their hosts. Exemplary reactions involving these enzymes are listed in Table , most of which are hydrolytic reactions.…”

Nanosized Building Blocks for Customizing Novel Antibiofilm Approaches

“…The polymeric nanostructure and biofilm diagrams were designed by Michael Osadciw, University of Rochester. ester]; Liu et al 2016). In the acidic microenvironment found in staphylococcal biofilms (pH 5), the protonation of the NE surface due to the presence of poly(β-amino ester) increases its penetration and further accumulation at the bacterial cellmedium interface.…”