*3.3. SEM Observations*

## 3.3.1. *L. monocytogenes* and *E. coli*

Cinnamon and trans-cinnamaldehyde were not used in these investigations due to their high inhibitor effect. For *Listeria* and *E. coli* only thyme EO and thymol were chosen based on results obtained for dual-species biofilm.

Control samples showed the complex structure of the formed biofilm (Figure 4A), namely, cells embedded in a large amount of possible extracellular polysaccharide (EPS) and forming a three-dimensional structure. Treatment with thyme and thymol resulted in damaged, anamorph, sparse micro-colonies and individual cells (Figure 4B–D).

**Figure 4.** *Listeria monocytogenes* and *Escherichia coli* biofilms observed using scanning electron microscope. (**A**) control, (**B**) thyme EOs (0.5 mg/mL), and (**C**,**D**) thymol (0.1 mg/mL).
