Table 3.
Susceptibility of P. aeruginosa biofilms to various treatments after 3 and 60 days of growth, determined by disk diffusion
| Material | Dose on disk (μg) | ZOI (mm) day 3 |
ZOI (mm) day 60 |
|---|---|---|---|
| Fe3O4 NPs† | 10 | 22/S | 21/S |
| 5 | 17.5/S | 16/S | |
| 2.5 | 11/R | 10/R | |
| Fe3O4@PEG NPs | 10 | 0/R | 0/R |
| 5 | 0/R | 0/R | |
| 2.5 | 0/R | 0/R | |
| Fe3O4@ALG NPs | 10 | 22/S | 22/S |
| 5 | 16/S | 15/S | |
| 2.5 | 10/R | 8/R | |
| Fe3O4@ALG:TOBRA NPs | 10 | 23/S | 22/S |
| 5 | 11/R | 15/I | |
| 2.5 | 7/R | 5/R | |
| ZVFe@ALG NPs | 10 | 25/S | 24/S |
| 5 | 21/S | 22/S | |
| 2.5 | 20/S | 20/S | |
| Tobramycin | 10* | 10/R | 0/R |
| 100** | 25/R** | 15/R** | |
| 1000** | 35/R** | 32/R** |
Interpretation: R resistant, I bintermediate, S susceptible, ZOI zone of inhibition, PEG polyethylene glycol, ALG alginate, TOBRA tobramycin, ZVFe zero-valent iron
†Uncapped NPs. *CLSI breakpoint for susceptibility of tobramycin by disk diffusion is 10 μg. Therefore, all colonies are found to be tobramycin resistant by CLSI standards. **Higher tobramycin doses in the disk were investigated to determine whether any susceptibility existed at higher doses. At present, there are no CLSI values/breakpoints for NPs as antimicrobial agents