Bactericidal Activity of Usnic Acid-Chitosan Nanoparticles against Persister Cells of Biofilm-Forming Pathogenic Bacteria.

Fazlurrahman Khan,Young-Mog Kim,Hongsik Yu

doi:10.3390/md18050270

Abstract

The present study aimed to prepare usnic acid (UA)-loaded chitosan (CS) nanoparticles (UA-CS NPs) and evaluate its antibacterial activity against biofilm-forming pathogenic bacteria. UA-CS NPs were prepared through simple ionic gelification of UA with CS, and further characterized using Fourier transform infrared spectroscopy, X-ray diffraction, and field-emission transmission electron microscopy. The UA-CS NPs presented a loading capacity (LC) of 5.2%, encapsulation efficiency (EE) of 24%, and a spherical shape and rough surface. The maximum release of UA was higher in pH 1.2 buffer solution as compared to that in pH 6.8 and 7.4 buffer solution. The average size and zeta potential of the UA-CS NPs was 311.5 ± 49.9 nm in diameter and +27.3 ± 0.8 mV, respectively. The newly prepared UA-CS NPs exhibited antibacterial activity against persister cells obtained from the stationary phase in batch culture, mature biofilms, and antibiotic-induced gram-positive and gram-negative pathogenic bacteria. Exposure of sub-inhibitory concentrations of UA-CS NPs to the bacterial cells resulted in a change in morphology. The present study suggests an alternative method for the application of UA into nanoparticles. Furthermore, the anti-persister activity of UA-CS NPs may be another possible strategy for the treatment of infections caused by biofilm-forming pathogenic bacteria.

Highlights

Studies have shown that the formation of persister cells by most pathogenic bacteria is a challenging task when treating infections using antimicrobial agents [1,2,3]
The encapsulation of usnic acid (UA) into the chitosan nanoparticles (CS NPs) was confirmed by release assay, FTIR, XRD, and FE-TEM
Different types of persisters such as stationary phase cells, persisters obtained from mature biofilms, and antibiotic-induced E. coli, P. aeruginosa, S. aureus, and L. monocytogenes cells were killed by the Minimum Inhibitory Concentration (MIC) and sub-MIC of UA-CS NPs

Summary

Introduction

Studies have shown that the formation of persister cells by most pathogenic bacteria is a challenging task when treating infections using antimicrobial agents [1,2,3]. Reports have shown that the formation of persister cells occurs stochastically as well as under several environmental factors, such as nutrient deficiency, oxidative stress, DNA damage, drop in cellular ATP, and sub-inhibitory concentration of antibiotics [1,3,7]. Apart from these factors, the biofilm environment provides additional protection against the entry of the antibiotic to the persister cells [8], which are encased beneath the biofilm matrix composed of extracellular polymeric substances (EPS) such as extracellular DNA, exopolysaccharide, and proteins [9]. Once the aforementioned environmental stress releases/drops, this subpopulation begins to multiply and recurrent infection occurs

Methods

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Discussion

Conclusion