Antibacterial assay
Staphylococcus aureus strain is purchased from ATCC (25923).S. aureus was cultured at +37°C in a Mueller Hinton Agar (BD) for
24 hours. Then on colony was transferred to 10 mL of Mueller Hinton
Broth (BD) for 24 hours at +37°C with agitation for preculture step. The
absorbance is read at 620 nm and we adjusted DO value to 0.001 to
perform our assay, corresponding to a density of 8.105CFU.mL-1. As cytotoxicity assay, we tested
PDA-PAR30 NPs in solution and also Gel-
PDA-PAR30 composite hydrogel. For solution part, we kept
the same ratio (samples:bacteria) in medium as 1 to 9, final volume is
100 µL (10µL of NPs for 90 µL of bacteria in medium). Samples with
bacteria were incubated for 24 hours at +37°C with agitation. Final
absorbance were read at 620 nm in order to quantify bacteria growth or
inhibition. For gelatin hydrogels part, samples were directly produced
in 48 wells-plate and sterilized by UV light exposure. After preculture
of S. aureus, we added 300 µL of suspension with OD=0.001 then we
incubated for 24 hours at +37°C with agitation. OD was read at 620 nm.
We compared PDA NPs and PDA-PAR30 NPs. In solution, OD
of samples (PDA and PDA-PAR30) with bacteria were
subtracted to OD the same samples without bacteria to remove PDA
absorption (brown solution). All results were compared to a normal
growth condition named “Bacteria”, defined as 100% growth. We also
tested Tris buffer (in solution or hydrogel) as a negative control. We
used antibiotics (Cefotaxime 0.1 µg.mL-1 +
Tetracycline 10 µg.mL-1) as positive control. We also
used PAR30 (10 µg.mL-1) without PDA as
positive control. All samples were performed in triplicates.