ferrites revealed a different behavior as compared with their
microbicidal properties (Figs. S1eS5). These compounds inhibited
the S. aureus biofilm development at low concentrations ranging
from 0.031 to 0.002 mg/mL, the most efficient being the S0 followed
by S6, S5 and S6-800 (Fig. S1).
All tested ferrites inhibited the E. faecalis biofilm development at
high concentrations ranging from 1 mg/mL to 0.063 mg/mL, the
most active inhibitors being the cobalt ferrites S4, S6 and S6-800
(Fig. S2).
All tested cobalt ferrites inhibited the development of E. coli
biofilms at lower concentrations from 0.008 to 0.002 mg/mL, and
S0 and S6 were also active at the highest tested concentration
(Fig. S3).
Among the tested ferrites only S6 exhibited inhibitory effect on
the P. aeruginosa biofilm development, but this effect was present
only at the highest tested concentration of 1 mg/mL (Fig. S4).
The anti-biofilm activity of the tested compounds against the
fungal strain was also very low, only S6 exhibiting anti-biofilm
activity at the highest tested concentration (Fig. S5).
The possible mechanisms for the antibacterial action of cobalt
ferrites could be represented by the adherence of these nanoparticles
to the bacterial cell wall and penetration through the cell
membrane, followed by the bacterial cell lysis. The large surface
area of nanoparticles enhances their bioactivity and makes them
effective bactericidal agents. Moreover, the generation of reactive
oxygen species could enhance the bacteria killing rate [52].