Selective Adsorption Of Nanospheres Onto Spherical Bacteria Endows Photodynamic Treatment With Narrow-Spectrum Activity

Accompanying the antimicrobial resistance crisis is a failure in new antimicrobial discovery.Narrow-spectrum antimicrobials and treatment modalities eradicate specifically the target pathogenic bacteria,thereby generating fewer off-target effects on the microbiome;nevertheless,their development is largely delayed by their relatively lack of profit and difficulties in preparation.Photodynamic therapy eliminates target cells with reactive oxygen species(ROS),thereby circumventing bacterial resistance mechanisms but is intrinsically a wide-spectrum modality.Herein,based on the review on the two antimicrobial therapies,we propose a new method of preparation of narrow-spectrum antimicrobial agents.The universality of the preparation method,the narrow-spectrum activity and the selection mechanism of the antibacterial agent were verified.The main research work is as follows:1.Selective adsorption of like-charged nanospheres on spherical bacteria.we found that like-charged nanospheres can selectively target spherical bacteria.Firstly,through the sedimentation experiments and phase diagram of the like-charged nanosphere-bacteria mixture,we found that the addition of nanospheres would cause the phase change of the mixture of spherical bacteria,but not rod-like bacteria.The synchrotron soft X-ray imaging experiment was used to explain this phenomenon,and the experimental results showed that this was because the nanospheres could specifically adsorb to the surface of the isotropic cocci rather than the surface of the anisotropic bacilli.And the charge and size asymmetry of the like-charged nanospheres-bacteria,leads to the selective adsorption of the nanospheres to the cocci,which is a recognition mechanism based on bacterial morphology selection driven by electrostatic interaction and entropy increasing aggregation.At the same time,we demonstrated that this selectivity of spherical bacteria is suitable for a variety of nanospheres with different compositions and surface chemistry.2.Preparation of narrow-spectrum photodynamic antibacterial agents.The imbalance of homeostasis of host symbiotic bacteria(most of which are bacilli)caused by the overgrowth of coccus can lead to a series of diseases.In this case,narrow-spectrum antibacterial agents and methods that can target coccus are very necessary to reduce the impact on the symbiotic bacteria.Here we present a nanosphere mediated method for converting photodynamic nanometer antimicrobials into narrow-spectrum antimicrobials.The nanospheres were loaded with photosensitizer(photodynamic nanosphere)so that can generate reactive oxygen species in situ upon irradiation.Combined with the extremely limited effective radii of action of ROS,photodynamic nanospheres only have a killing effect on spherical bacteria which nanosphere adsorbed on,thus achieving the narrow-spectrum antibacterial effect.Through bactericidal experiments,we proved that the prepared narrow-spectrum photodynamic nano-antibacterial agent has a good bactericidal'teffect on spherical bacteria(>99%),and almost no bactericidal effect on rod-like(<1%).In addition,by changing the type of photosensitizer loaded,the material of the carrier nanosphere,and the type of cell membrane covered on the nanosphere,we proved that the antibacterial agent's spherical bacteria selectivity is only a physical shape selectivity driven by entropy increase.It proves that we have successfully developed a universal method for the conversion of broad-spectrum photodynamic antimicrobial agents into narrow-spectrum antimicrobial agents.