Streptomycin Sulfate-Loaded Niosomes Enables Increased Antimicrobial and Anti-Biofilm Activities

Abstract

One of the antibiotics used to treat infections is streptomycin sulfate that inhibits both Gram-negative and -positive bacteria. Nanoparticles are suitable carriers for the direct delivery and release of drug agents to infected locations. Niosomes are one of the new drug delivery systems that have received much attention today due to their excellent biofilm penetration property and controlled release. In this study, niosomes containing streptomycin sulfate were prepared by using the thin layer hydration method and optimized based on the size, polydispersity index (PDI), and encapsulation efficiency (EE%) characteristics. It was found that the Span 60-to-Tween 60 ratio of 1.5 and the surfactant-to-cholesterol ratio of 1.02 led to an optimum formulation with a minimum of size, low PDI, and maximum of EE of 97.8 nm, 0.27, and 86.7%, respectively. The drug release investigation showed that 50.0 ± 1.2% of streptomycin sulfate was released from the niosome in 24 h and reached 66.4 ± 1.3% by the end of 72 h. Two-month stability studies at 25° and 4°C showed more acceptable stability of samples kept at 4°C. Consequently, antimicrobial and anti-biofilm activities of streptomycin sulfate-loaded niosomes against Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa were found significantly higher than those of free drug, and the minimum inhibitory concentration values decreased 4- to 8-fold. Furthermore, niosome-encapsulated streptomycin up to 1,500 μg/ml exhibited negligible cytotoxicity against the human foreskin fibroblasts cell line, whereas the free drug exhibited slight cytotoxicity at this concentration. Desired physical characteristics and low toxicity of niosomal nano-carriers containing streptomycin sulfate made them a demanded candidate for the treatment of current bacterial infections and biofilms.

Keywords: anti-biofilm; antimicrobial; cytotoxicity; niosome; streptomycin sulfate.

FIGURE 1

Response surfaces for (A) average diameter, (B) entrapment efficiency (EE), and (C) polydispersity index (PDI) as an outcome of Span 60-to-Tween 60 and surfactant-to-cholesterol molar ratios.

FIGURE 2

Morphological characterization of optimized niosomes by SEM.

FIGURE 3

Effect of different temperatures of storage on the average diameter (A), polydispersity index (PDI) (B), and streptomycin sulfate encapsulation efficiency (EE%) (C) n = 3, *p value < 0.05, **p value < 0.01, and ***p value <0.001.

FIGURE 4

The release profile of free and optimized niosomal formulation of streptomycin sulfate. Each point represents the mean ± SD (n = 3).

FIGURE 5

MIC (A) and MBC (B) of free and niosome-encapsulated streptomycin sulfate. n = 3.

FIGURE 6

Antibacterial activity of free streptomycin and encapsulated streptomycin against pathogenic bacteria: S. aureus (A), E. coli (B), and P. aeruginosa (C) measured by optical density as a function of time (72 h). Each point corresponds to a mean ± SD with three replicates per condition.

FIGURE 7

Anti-biofilm activity of free and niosome-encapsulated streptomycin sulfate against selected pathogenic bacterial biofilms at their minimal inhibition concentrations shown in Figure 5. Biofilms were formed in a 96-well microplate and, consequently, treated for 24 h at 37°C. The remaining biofilm was quantified by CV staining and compared with the untreated one. Data represent the mean ± SD (n = 3). Error bars represent standard deviations. The levels of significant difference are denoted by *p value < 0.05, **p value < 0.01, and ***p value < 0.001.

FIGURE 8

Cytotoxicity of free and niosomal streptomycin sulfate in different concentration against HFF after 24 h. ***p < 0.001, **p < 0.01, *p < 0.05.