Eradicating antibiotic-resistant biofilms with silver-conjugated superparamagnetic iron oxide nanoparticles.

Concerns about antibiotic-resistant microorganisms, such as methicillin-resistant Staphylococcus aureus (MRSA), is causing a resurgence in the search for novel strategies which can eradicate infections without the use of antibiotics. In this study, the unique magnetic and antibacterial properties of superparamagnetic iron oxide nanoparticles (SPION) and silver have been combined through the design of silver-conjugated SPION. For the first time, it is demonstrated that MRSA biofilms can be eradicated by silver-conjugated SPION without resorting to the use of antibiotics. A significant decrease in biofilm mass, which corresponds to a seven orders of magnitude decrease in viability, is observed when MRSA biofilms are treated with 1 mg/mL of silver-conjugated SPION (p < 0.01). Moreover, SPION anti-biofilm efficacy is further improved in the presence of an external magnetic field. The anti-biofilm property of silver-conjugated SPION treatment is due to the significant increases in intracellular or membrane-bound iron (p < 0.001), sulfur (p < 0.05), and silver (p < 0.001) concentrations, thus increases in SPION uptake within the biofilms. For this reason, this study demonstrates for the first time that silver-conjugated SPION could be used as a targeted antibacterial therapy to the infection site. Thus, this novel infection eradication strategy holds great promise to be an alternative to the antibiotic of last resort, vancomycin, which bacteria have already started to develop a resistance towards.