Stimuli-Responsive Nanoplatform-Assisted Photodynamic Therapy Against Bacterial Infections

Antibiotics and Bacterial Resistance-A Short Story of an Endless Arms Race

Despite the undisputed development of medicine, antibiotics still serve as first-choice drugs for patients with infectious disorders. The widespread use of antibiotics results from a wide spectrum of their actions encompassing mechanisms responsible for: the inhibition of bacterial cell wall biosynthesis, the disruption of cell membrane integrity, the suppression of nucleic acids and/or proteins synthesis, as well as disturbances of metabolic processes. However, the widespread availability of antibiotics, accompanied by their overprescription, acts as a double-edged sword, since the overuse and/or misuse of antibiotics leads to a growing number of multidrug-resistant microbes. This, in turn, has recently emerged as a global public health challenge facing both clinicians and their patients. In addition to intrinsic resistance, bacteria can acquire resistance to particular antimicrobial agents through the transfer of genetic material conferring resistance. Amongst the most common bacterial resistance strategies are: drug target site changes, increased cell wall permeability to antibiotics, antibiotic inactivation, and efflux pumps. A better understanding of the interplay between the mechanisms of antibiotic actions and bacterial defense strategies against particular antimicrobial agents is crucial for developing new drugs or drug combinations. Herein, we provide a brief overview of the current nanomedicine-based strategies that aim to improve the efficacy of antibiotics.

Efficient antibacterial AIEgens induced ROS for selective photodynamic treatment of bacterial keratitis

Bacterial keratitis (BK) is an acute infection of the cornea, accompanied by uneven epithelium boundaries with stromal ulceration, potentially resulting in vision loss. Topical antibiotic is the regular treatment for BK. However, the incidence rate of multidrug-resistant bacteria limits the application of traditional antibiotics. Therefore, a cationic aggregation-induced emission luminogens (AIEgens) named TTVP is utilized for the treatment of BK. TTVP showed no obvious cytotoxicity in maintaining the normal cell morphology and viability under a limited concentration, and revealed the ability to selectively combine with bacteria in normal ocular environment. After light irradiation, TTVP produced reactive oxygen species (ROS), thus exerting efficient antibacterial ability in vitro. What's more, in rat models of Staphylococcus aureus (S. aureus) infection, the therapeutic intervention of TTVP lessens the degree of corneal opacity and inflammatory infiltration, limiting the spread of inflammation. Besides, TTVP manifested superior antibacterial efficacy than levofloxacin in acute BK, endowing its better vision salvage ability than conventional method. This research demonstrates the efficacy and advantages of TTVP as a photodynamic drug in the treatment of BK and represents its promise in clinical application of ocular infections.

Biodegradable MoO x @MB incorporated hydrogel as light-activated dressing for rapid and safe bacteria eradication and wound healing

Wounds infected with drug-resistant bacteria are hard to treat, which remains a serious problem in clinical practice. An innovative strategy for treating wound infections is thus imperative. Herein, we describe the construction of a nanocomposite from biocompatible poly(vinyl alcohol) (PVA)/polyethylene glycol (PEG) hydrogel loaded biodegradable MoO_x nanoparticles (NPs) and photosensitizer methylene blue (MB), denoted as MoO_x@MB-hy. By incorporating MoO_x@MB NPs, the nanocomposite hydrogel can act as a photoactivated wound dressing for near-infrared-II 1064 nm and 660 nm laser synergetic photothermal–photodynamic therapy (PTT–PDT). The key to PTT-induced heat becomes the most controllable release of MB from MoO_x@MB-hy to produce more ¹O₂ under 660 nm irradiation. Importantly, MoO_x@MB-hy can consume glutathione (GSH) and trap bacteria nearer to the distance limit of ROS damage to achieve a self-migration-enhanced accumulation of reactive oxygen species (ROS), thereby conquering the intrinsic shortcomings of short diffusion distance and lifetime of ROS. Consequently, MoO_x@MB-hy has high antibacterial efficiencies of 99.28% and 99.16% against Amp^rE. coli and B. subtilis within 15 min. Moreover, the light-activated strategy can rapidly promote healing in wounds infected by drug-resistant bacteria. This work paves a way to design a novel nanocomposite hydrogel dressing for safe and highly-efficient antibacterial therapy.

A photoactivated MoO_x@MB-hy hydrogel was constructed with synergistic photothermal–photodynamic therapy properties for enhanced ROS accumulation on a bacterial surface to rapidly eradicate bacteria and accelerate the healing of wounds infected by drug-resistant bacteria.