Health-care-associated infections and the development of antimicrobial resistance are one of the most serious public health problems worldwide. Bacterial infections are often difficult to treat because the bacteria can adapt rapidly to conventional antibiotics (ABs), which in turn has made their choice limited and expensive. Nowadays, nanotechnology holds great promise for the design of new antimicrobials, reducing the use of existing ABs, development of AB-resistant "superbugs" and the spread of pathogenic microbes in healthcare facilities. One of the biomedically promising biopolymers is chitosan, which has gained interest in the design of wound dressings and implants, mainly due to its biocompatibility, biodegradability, antimicrobial and immune-modulating properties. Crosslinking of chitosan with biocidal metal-based nanoparticles, such as Ag or Cu can be a promising approach to create novel nano-antimicrobials that have both antimicrobial and immune-modulating effects.
The aim of the study was to (i) synthesize Ag-chitosan-nanocomposites (CS-AgNPs) and (ii) evaluate their antimicrobial potency and mode of action against the medically important bacteria Gram (-) Escherichia coli and Pseudomonas aeruginosa, and Gram (+) Staphylococcus aureus. In parallel, AgNO₃ and chitosan were analyzed as ionic and coating/stabilizer control.
CS-AgNPs were synthesized by reduction of AgNO₃ with trisodium citrate in the presence of chitosan (Sigma, low molecular weight). Three types of CS-AgNPs with different silver to chitosan weight ratios (1:0.3, 1:1 and 1:3) were synthesized. The antimicrobial potency of CS-AgNPs was addressed by determining their minimum biocidal concentration (MBC) in deionized water to minimize the effect of silver ions speciation on its bioavailability and toxicity. Flow-cytometry and laser-scanning confocal microscopy (LSCM) was used to assess nanocomposite cell interactions.
We showed that the studied CS-AgNPs were effective antimicrobials against E. coli, P. aeruginosa, and S. aureus: 24-h MBC values ranged from 0.07 – 0.19 mg Ag/L, 0.31 – 0.63, and 0.50 – 0.69 mg Ag/L, respectively, and the antibacterial potency depends on the chitosan content. Flow-cytometry and CLSM study revealed the CS-AgNPs attachment onto the surface of bacteria.