Nutrient agar

Dopamine hydrochloride, ammonium hydroxide (38–40%) and ethanol were purchased from Sigma-Aldrich (Pty. Ltd., Sydney, NSW, Australia). Gentamicin sulphate was purchased from AK Scientific (Union city, CA, USA). Chromatography grade acetonitrile, ammonium formate and formic acid were purchased from Sigma-Aldrich. All the solutions used in the following experiments were prepared from Milli Q water (Millipore Simplicity system) having a resistivity of 18.2 MΩ cm. Nutrient agar and Nutrient broth were supplied by Acumedia (Melbourne, Australia). The microbial species tested were S. aureus (ATCC 25923) and P. aeruginosa (ATCC 9721).

Bacterial strains, S. aureus ATCC 25923, E. coli ATCC 25922, S. Enteritidis ATCC 13076, S. Typhimurium ATCC 13311, and S. Typhimurium UK-1 ATCC 68169, were inoculated in nutrient broth (Acumedia, Lansing, MI, USA, USA), and incubated at 37 °C for 24 h. Cultures reached a concentration of 10⁹ CFU/mL. After the growth, the bacterial strains were serially diluted in a saline 10-fold solution up to 10⁻⁷, and dilution was plated in nutrient agar to confirm the total CFUs. A volume of 10 µL of each dilution was placed on the film’s square with and without bio-AgNP and stored in a sterile Petri dish at room temperature for 24 h. The initial cellular density in contact with films ranged from 10⁶ CFU/cm² to 1 CFU/cm². After contact with bacteria, film samples were inoculated in nutrient broth and placed at 37 °C for 24 h. Bacterial growth was confirmed by samples plating in agar medium, E. coli in MacConkey Agar (Acumedia, Lansing, MI, USA, USA), S. aureus in Mannitol Salt Agar (Difco^®, Tucker, GA, USA), and Salmonella sp. in SS Agar (Difco^®, Tucker, GA, USA).