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Silver nanoparticles-chitosan composites activity against resistant bacteria: tolerance and biofilm inhibition.

ABSTRACT: This study aimed to evaluate the effectiveness of silver nanoparticles-chitosan composites (AgNPs) with different morphologies and particle size distributions against resistant bacteria and biofilm formation. Four different samples were prepared by a two-step procedure using sodium borohydride and ascorbic acid as reducing agents and characterized by UV-Vis absorption spectra, scanning transmission electron microscopy. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the AgNPs were determined according to the Clinical and Laboratory Standards Institute (CLSI) against clinical isolates multidrug-resistant and strains of the American Type Culture Collection (ATCC). An assay was performed to determine the MICs during 20 successive bacteria exposures to AgNPs to investigate whether AgNPs induce tolerance in bacteria. The antibiofilm activities of AgNPs were also evaluated by determining the minimum biofilm inhibitory concentration (MBIC). The spherical AgNPs present diameters ranging from 9.3 to 62.4 nm, and some samples also have rod-, oval-, and triangle-shaped nanoparticles. The MIC and MBC values ranged from 0.8 to 25 μg/mL and 3.1 to 50 μg/mL, respectively. Smaller and spherical AgNPs exhibited the highest activity, but all the AgNPs developed in this study exhibit bactericidal activity. There was no significant MIC increase after 20 passages to the AgNPs. Regarding the antibiofilm activity, MBICs ranged from 12.5 to 50 μg/mL. Again, smaller and spherical nanoparticles presented the best results with phenotypic inhibition of production of slime or exopolysaccharide (EPS) matrix. Thus, it was concluded that AgNPs have a promising potential against resistant bacteria and bacteria that grow on biofilms without inducing tolerance.

Supplementary information

The online version contains supplementary material available at 10.1007/s11051-021-05314-1.

SUBMITTER: Dos Santos EMP

PROVIDER: S-EPMC8383018 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:As the threat of antimicrobial-resistant bacteria compromises the safety and efficacy of modern healthcare practices, the search for effective treatments is more urgent than ever. For centuries, silver (Ag) has been known to have antibacterial properties and, over the past two decades, Ag-based nanoparticles have gained traction as potential antimicrobials. The antibacterial efficacy of Ag varies with structure, size, and concentration. In the present study, we examined Ag nanoparticles (AgNPs) for their antimicrobial activity and safety. We compared different commercially-available AgNPs against gram-negative Escherichia coli, Pseudomonas aeruginosa, Acinetobacter baumannii, and gram-positive Staphylococcus aureus methicillin-resistant and susceptible strains. The most effective formula of AgNPs tested had single-digit (μg/mL) minimum inhibitory concentrations against gram-negative multidrug-resistant clinical bacterial isolates with novel and emerging mechanisms of resistance. The mode of killing was assessed in E. coli and was found to be bactericidal, which is consistent with previous studies using other AgNP formulations. We evaluated cytotoxicity by measuring physiological readouts using the Caenorhabditis elegans model and found that motility was affected, but not the lifespan. Furthermore, we found that at their antibacterial concentrations, AgNPs were non-cytotoxic to any of the mammalian cell lines tested, including macrophages, stem cells, and epithelial cells. More interestingly, our experiments revealed synergy with clinically relevant antibiotics. We found that a non-toxic and non-effective concentration of AgNPs reduced the minimum inhibitory concentrations of aminoglycoside by approximately 22-fold. Because both aminoglycosides and Ag are known to target the bacterial ribosome, we tested whether Ag could also target eukaryotic ribosomes. We measured the rate of mistranslation at bactericidal concentration and found no effect, indicating that AgNPs are not proteotoxic to the host at the tested concentrations. Collectively, our results suggest that AgNPs could have a promising clinical application as a potential stand-alone therapy or antibiotic adjuvants.

Project description:Biofilms are surface-associated microbial communities known for their increased resistance to antimicrobials and host factors. This resistance introduces a critical clinical challenge, particularly in cases associated with implants increasing the predisposition for bacterial infections. Preventing such infections requires the development of novel antimicrobials or compounds that enhance bactericidal effect of currently available antibiotics. We have synthesized and characterized twelve novel silver(I) cyanoximates designated as Ag(ACO), Ag(BCO), Ag(CCO), Ag(ECO), Ag(PiCO), Ag(PICO) (yellow and red polymorphs), Ag(BIHCO), Ag(BIMCO), Ag(BOCO), Ag(BTCO), Ag(MCO) and Ag(PiPCO). The compounds exhibit a remarkable resistance to high intensity visible light, UV radiation and heat and have poor solubility in water. All these compounds can be well incorporated into the light-curable acrylate polymeric composites that are currently used as dental fillers or adhesives of indwelling medical devices. A range of dry weight % from 0.5 to 5.0 of the compounds was tested in this study. To study the potential of these compounds in preventing planktonic and biofilm growth of bacteria, we selected two human pathogens (Gram-negative Pseudomonas aeruginosa and Gram-positive Staphylococcus aureus) and Gram-positive environmental isolate Bacillus aryabhattai. Both planktonic and biofilm growth was abolished completely in the presence of 0.5% to 5% of the compounds. The most efficient inhibition was shown by Ag(PiCO), Ag(BIHCO) and Ag(BTCO). The inhibition of biofilm growth by Ag(PiCO)-yellow was confirmed by scanning electron microscopy (SEM). Application of Ag(BTCO) and Ag(PiCO)-red in combination with tobramycin, the antibiotic commonly used to treat P. aeruginosa infections, showed a significant synergistic effect. Finally, the inhibitory effect lasted for at least 120 h in P. aeruginosa and 36 h in S. aureus and B. aryabhattai. Overall, several silver(I) cyanoximates complexes efficiently prevent biofilm development of both Gram-negative and Gram-positive bacteria and present a particularly significant potential for applications against P. aeruginosa infections.

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Silver nanoparticles-chitosan composites activity against resistant bacteria: tolerance and biofilm inhibition.

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