The excessive use of antibiotics in both human and veterinary medicine has contributed to the development and rapid spread of drug resistance in bacteria. Silver nanoparticles (AgNPs) have become a tool of choice that can be used to treat these resistant bacteria. Several studies have shown that AgNPs have antibacterial and wound healing properties. In this study, we evaluated the biological activity of anisotropic AgNPs to develop an antimicrobial gel formulation for treating wound infections. We showed that some anisotropic AgNPs (S2) have an effective antibacterial activity against bacterial pathogens and low cytotoxicity to keratinocytes and fibroblasts in vitro. The MIC and MBC values were in the range of 2–32 µg/mL, and cytotoxicity had IC₅₀ values of 68.20 ± 9.71 µg/mL and 68.65 ± 10.97 µg/mL against human keratinocyte and normal human dermal fibroblast cells, respectively. The anisotropic AgNPs (S2) were used as a gel component and tested for antibacterial activity, including long-term protection, compared with povidone iodine, a common antiseptic agent. The results show that the anisotropic AgNPs can inhibit the growth of most tested bacterial pathogens and provide protection longer than 48 h, whereas povidone iodine only inhibits the growth of some bacteria. This study suggests that anisotropic AgNPs could be used as an alternative antimicrobial agent for treating bacterial skin infection and as a wound healing formulation.

Burkholderia pseudomallei is the causative pathogen of melioidosis and this bacterium is resistant to several antibiotics. Silver nanoparticles (AgNPs) are an interesting agent to develop to solve this bacterial resistance. Here, we characterize and assess the antimelioidosis activity of AgNPs against these pathogenic bacteria. AgNPs were characterized and displayed a maximum absorption band at 420 nm with a spherical shape, being well-monodispersed and having high stability in solution. The average size of AgNPs is 7.99 ± 1.46 nm. The antibacterial efficacy of AgNPs was evaluated by broth microdilution. The bactericidal effect of AgNPs was further assessed by time-kill kinetics assay. Moreover, the effect of AgNPs on the inhibition of the established biofilm was investigated by the crystal violet method. In parallel, a study of the resistance induction development of B. pseudomallei towards AgNPs with efflux pump inhibiting effect was performed. We first found that AgNPs had strong antibacterial activity against both susceptible and ceftazidime-resistant (CAZ-resistant) strains, as well as being efficiently active against B. pseudomallei CAZ-resistant strains with a fast-killing mode via a bactericidal effect within 30 min. These AgNPs did not only kill planktonic bacteria in broth conditions, but also in established biofilm. Our findings first documented that the resistance development was not induced in B. pseudomallei toward AgNPs in the 30th passage. We found that AgNPs still showed an effective efflux pump inhibiting effect against these bacteria after prolonged exposure to AgNPs at sublethal concentrations. Thus, AgNPs have valuable properties for being a potent antimicrobial agent to solve the antibiotic resistance problem in pathogens.

The presence of biofilm within a chronic wound may delay the healing process. Thus, control of biofilm formation and providing bactericidal effect are crucial factors for wound healing management. Alginate-based nanocomposite hydrogels have been suggested as dressing materials for wound treatment, which are employed as a biocompatible matrix. Therefore, in this study, we aimed to develop a biocompatible antimicrobial wound dressing containing AgNPs and demonstrate its efficacy against polymicrobial wound biofilms by using a biofilm flow device to simulate a chronic infected, exuding wound and specific wound environment. The results from agar well diffusion, the Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) assays showed that TA-AgNPs exhibited antibacterial activity against wound pathogens. Additionally, the Minimum Biofilm Eradication Concentration assay (MBEC) demonstrated it could impair biofilm formation. Importantly, our TA-AgNPs/Alginate hydrogel clearly showed antibacterial activities against Streptococcus pyogenes, Staphylococcus aureus and Pseudomonas aeruginosa. Furthermore, we used the biofilm flow device to test the topical antimicrobial hydrogel against a three-species biofilm. We found that TA-AgNPs/Alginate hydrogel significantly showed a 3–4 log reduction in bacterial numbers when applied with multiple doses at 24 h intervals, and was especially effective against the chronic wound pathogen P. aeruginosa. This work highlighted that the TA-AgNPs/Alginate hydrogel is a promising material for treating complex wound biofilms.

Staphylococcus pseudintermedius (S. pseudintermedius) infected wounds can cause seriously delayed wound healing processes in animals. Antimicrobial agents that have antimicrobial and wound healing efficacy have become an essential tool for overcoming this problem. In our previous study, anisotropic AgNPs have been reported to have antimicrobial efficiency against animal and human pathogens, and could be suitable as antimicrobial agents for infected wounds. Here, antimicrobial and wound healing activities of anisotropic AgNPs gels were assessed in vivo. BALB/cAJcl mice wounds were infected by Methicillin-resistant Staphylococcus pseudintermedius (MRSP). Then, antibacterial and wound healing activities were evaluated by bacterial cell count, wound contraction, digital capture, and histology. The results show that anisotropic AgNPs gels could eliminate all bacterial cell infected wounds within 7 days, the same as povidone iodine. Wound healing activity was evaluated by wound contraction (%). The results showed 100% wound contraction in groups treated with anisotropic AgNPs gels within 14 days that was not significantly different from povidone iodine and control gel without AgNPs. However, the digital capture of wounds on day 4 showed that anisotropic AgNPs gel prevented pus formation and reduced scar appearance within 21 days. The histology results exhibit improved collagen fiber alignment that supports scar disappearance. In conclusion, these results indicate that anisotropic AgNPs gels are suitable for treating infected wounds. The gel is effective in eliminating bacteria that supports the natural process of wound repair and also causes reduced scar formation.

Lipopeptides have been extensively studied as potential antimicrobial agents. In this study, we focused on the C₁₄-KYR lipopeptide, a modified version of the KYR tripeptide with myristic acid at the N-terminus. Here, membrane perturbation of live E. coli treated with the parent KYR and C₁₄-KYR peptides was compared at the nanoscale level using AFM imaging. AFM analyses, including average cellular roughness and force spectroscopy, revealed the severe surface disruption mechanism of C₁₄-KYR. A loss of surface roughness and changes in topographic features included membrane shrinkage, periplasmic membrane separation from the cell wall, and cytosolic leakage. Additional evidence from synchrotron radiation FTIR microspectroscopy (SR-FTIR) revealed a marked structural change in the membrane component after lipopeptide attack. The average roughness of the E. coli cell before and after treatment with C₁₄-KYR was 129.2 ± 51.4 and 223.5 ± 14.1 nm, respectively. The average rupture force of the cell treated with C₁₄-KYR was 0.16 nN, four times higher than that of the untreated cell. Our study demonstrates that the mechanistic effect of the lipopeptide against bacterial cells can be quantified through surface imaging and adhesion force using AFM.

Infectious diseases still represent an important cause of mortality for humans. One of the main reasons is that various pathogenic bacteria can persist and survive on inanimate surfaces for many days. Therefore, self-disinfection coating technology has become of interest to deal with this problem. In this research, we propose to develop a self-disinfection coating containing AgNPs-chitosan composite in 50% water-based polyurethane (WPU), which has a strong short- and long-term antibacterial effect. The coating agent was synthesized by conventional composite approaches. The physical and chemical properties of AgNPs-chitosan nanocomposite are studied by TEM, SEM, and FTA 100 Drop Shape Instrument B Frame System. The results show that at a concentration of 39 μg/mL, when reducing the size of AgNPs from 7.29 ± 1.65 to 4.66 ± 2.08 nm, the shape of a sphere turns into an asymmetrical circle and leads to increasing aggregation of AgNPs. Negative charges on the surface of AgNPs interact with amine (-NH₂) and hydroxyl (-OH) groups of chitosan through an electrostatic force. All formulations of the coating showed low hydrophobicity properties. Moreover, the short- and long-term antibacterial activity of the coating were investigated by application of the ISO 22196 standard protocol. The mean inhibition percentage of E. coli O157:H7 and S. aureus ATCC25722 of the formulation containing AgNPs at a concentration of 1280 µg/mL and 50% v/v of WPU (Formula 4) and the formulation containing AgNPs at a concentration of 1280 µg/mL, chitosan 39 µg/mL and 50% v/v of WPU (Formula 8) from 1 day to 4 months after the coating completely dried was 81.72% ± 3.15% and 82.07% ± 3.01% on E. coli O157:H7, 84.64% ± 2.59% and 83.27% ± 3.12% on S. aureus ATCC25722, respectively. There was no significant difference from statistical analysis at 95% confidence interval (p < 0.05). Furthermore, the quantify of silver ion from coating was measured by ICP-MS. The result reveal that the formulation containing AgNPs at a concentration of 1280 µg/mL, chitosan 39 µg/mL and 50% v/v of WPU (Formula 8) released an amount of silver ion lower than the formulation containing AgNPs at a concentration of 1280 µg/mL and 50% v/v of WPU (Formula 4) by approximately 5.92 times, while the same concentration of AgNPs and inhibition efficacy was not significantly different. In addition, such a concentration was non-toxic on NHDF cells, which were investigated by MTT assay. Therefore, formulation containing AgNPs at a concentration of 1280 µg/mL, chitosan 39 µg/mL and 50% v/v of WPU coating (Formula 8) will be further developed into commercial self-disinfection coatings.