Surface charge modulation of rifampicin-loaded PLA nanoparticles to improve antibiotic delivery in Staphylococcus aureus biofilms

David Da Costa,Charlotte Primard,Chloé Exbrayat-Héritier,Bernard Verrier,Simon Megy,Raphaël Terreux,Basile Rambaud

doi:10.1186/s12951-020-00760-w

Abstract

BackgroundAfter the golden age of antibiotic discovery, bacterial infections still represent a major challenge for public health worldwide. The biofilm mode of growth is mostly responsible for chronic infections that current therapeutics fail to cure and it is well-established that novel strategies must be investigated. Particulate drug delivery systems are considered as a promising strategy to face issues related to antibiotic treatments in a biofilm context. Particularly, poly-lactic acid (PLA) nanoparticles present a great interest due to their ability to migrate into biofilms thanks to their submicronic size. However, questions still remain unresolved about their mode of action in biofilms depending on their surface properties. In the current study, we have investigated the impact of their surface charge, firstly on their behavior within a bacterial biofilm, and secondly on the antibiotic delivery and the treatment efficacy.ResultsRifampicin-loaded PLA nanoparticles were synthetized by nanoprecipitation and characterized. A high and superficial loading of rifampicin, confirmed by an in silico simulation, enabled to deliver effective antibiotic doses with a two-phase release, appropriate for biofilm-associated treatments. These nanoparticles were functionalized with poly-l-lysine, a cationic peptide, by surface coating inducing charge reversal without altering the other physicochemical properties of these particles. Positively charged nanoparticles were able to interact stronger than negative ones with Staphylococcus aureus, under planktonic and biofilm modes of growth, leading to a slowed particle migration in the biofilm thickness and to an improved retention of these cationic particles in biofilms. While rifampicin was totally ineffective in biofilms after washing, the increased retention capacity of poly-l-lysine-coated rifampicin-loaded PLA nanoparticles has been associated with a better antibiotic efficacy than uncoated negatively charged ones.ConclusionsCorrelating the carrier retention capacity in biofilms with the treatment efficacy, positively charged rifampicin-loaded PLA nanoparticles are therefore proposed as an adapted and promising approach to improve antibiotic delivery in S. aureus biofilms.

Highlights

Despite a relentless fight against infectious agents that have caused high mortality and morbidity rates all around the world for centuries, the perpetual emergence of new microbes makes infectious diseases a major public health burden representing constant challenges for humanDa Costa et al J Nanobiotechnol (2021) 19:12 survival and life quality [1]
Tolerance toward antibiotics is multifactorial: (1) the biofilm matrix acts as a barrier against antibiotics due to its physicochemical properties, (2) the microenvironment with gradients of pH, oxygen and nutrients can alter antibiotic effects and (3) the presence of persister bacteria which exist in a dormant state and are insensitive to antibiotic treatments
Plain poly-lactic acid (PLA) NPs displayed an average size of 118 nm, as measured by dynamic light scaterring (DLS), and a zeta potential of -55 mV, characterizing a highly negative surface charge (Fig. 1a)

Summary

Introduction

Despite a relentless fight against infectious agents that have caused high mortality and morbidity rates all around the world for centuries, the perpetual emergence of new microbes makes infectious diseases a major public health burden representing constant challenges for humanDa Costa et al J Nanobiotechnol (2021) 19:12 survival and life quality [1]. Biofilms are defined as sessile and organized communities of single or multi-species bacteria adhering to biotic or abiotic surfaces and living within an auto-produced matrix of extracellular polymeric substances composed of polysaccharides, proteins, nucleic acids and lipids [3]. Such lifestyle allows bacteria to escape the immune system and may require up to 1,000 times the minimal inhibitory concentration of antibiotics for an effective treatment, leading to therapeutic failures [4]. We have investigated the impact of their surface charge, firstly on their behavior within a bacterial biofilm, and secondly on the antibiotic delivery and the treatment efficacy

Methods

Results

Conclusion