3.3.8. Antimicrobial Activity

The antibacterial efficiency of the PCL-based films against *S. aureus* and *E. coli* is presented in Table 3. The plain PCL film did not exhibit any antibacterial activity (R < 0.5) as expected. Inhibition effects on the bacterial growth were successfully induced by the incorporation of SE into the PCL matrix. Interestingly, complete biocidal effect on *S. aureus* (no viable counts) was detected after 24 h of exposure to any of the films containing SE. On the other hand, the results indicated a higher resistance of *E. coli* towards the films. This behavior is in concordance with the results obtained for the unloaded extract and attributed to the more complex cell wall of *E. coli* as a Gram negative bacteria compared to the cell wall of *S. aureus* as a Gram positive bacteria. Thus, the inhibition effect on *E. coli* was dependent on the SE content in the films. In particular, *E. coli* was slightly inhibited (0.5 ≤ R < 1) when in contact with the films containing 5% and 10% SE, while strong inhibition (R > 3) was achieved when in contact with the film loaded with 20% SE. Therefore, the strong antibacterial surface against foodborne pathogens was obtained by incorporating 20% SE into the PCL matrix, which reveals its remarkable potential for antimicrobial food packaging applications.


 biocidal effect

 biocidal

 biocidal

**Table 3.** Antimicrobial activity against *S. aureus* and *E. coli* of the PCL-based films.

 CFU—Colony Forming Units; R—Surface Reduction.

effect

effect

 6.36 ± 0.13

 6.18 ± 0.16

 2.40 ± 0.52

 0.73

 0.91

 4.69
