3.3.3. *L. monocytogenes* and *P. putida*

For *Listeria* and *P. putida* only thyme EO and thymol were chosen based on results obtained for dual-species biofilm.

Figure 6A,B present the findings for control samples with nascent and fully formed cell-to-cell connections and EPS material formation. Treatment with marjoram and its major component, terpinen-4-ol, resulted in significant changes in the composition of these structures, leaving mainly damaged cells and cell debris to be observed (Figure 6C,D).

**Figure 5.** *Listeria monocytogenes* and *Staphylococcus aureus* biofilms observed using scanning electron microscope. (**A**,**B**) control, (**C**) marjoram essential oil (EO) (1.6 mg/mL), (**D**) terpinen-4-ol (8 mg/mL), (**E**) thyme EO (0.4 mg/mL), and (**F**) thymol (0.8 mg/mL).

**Figure 6.** *Listeria monocytogenes* and *Pseudomonas putida* biofilms observed using scanning electron microscope. (**A**,**B**) control, (**C**) marjoram EO (1 mg/mL), and (**D**) terpinen-4-ol (1 mg/mL).

Scanning electron microscopy images demonstrate the structural changes caused by EOs or components during biofilm development [36]. The three-dimensional structure of matured biofilms disappeared after EO treatment, the cells were damaged, and most of the treated cells had burst.
