Biofilm-Forming Capacity of ESBL Escherichia coli and Influential Factors and Efficacy of Essential Oils in Inhibition and Disruption

Background/Objectives: The presence of extended-spectrum β-lactamase-producing Escherichia coli (ESBL-producing E. coli) is a major global concern as it causes hard-to-treat infections that can sometimes be life-threatening. Methods: Using the drop plate method, we examined which essential oils (EOs) were effective against the tested strains. After mapping the general biofilm-forming affinity of the isolates, we attempted to degrade the biofilm using the EOs. Results: Certain EOs can kill ESBL-producing E. coli, inhibit biofilm formation, and degrade mature biofilms. The drop plate method showed that 50 (83%) and 54 (90%) of the 60 tested EOs were effective against 20 different human and porcine ESBL-producing E. coli isolates when applied at 1% and 5%, respectively. The most effective ESBL-producing E. coli isolate (23R20) was used for anti-biofilm testing. The temperature of 37 °C was most effective in inhibiting and degrading biofilms, although this was markedly influenced by the carrier medium. Ajowan, cinnamon, oregano, and thyme had outstanding effects in both tests, inhibiting and degrading biofilms by 99%, respectively. Morphological differences (e.g., deformation, elongation or shortening of cells, amorphous structures, and ‘ghost’/perforated cells) were noted in the 23R20 E. coli cells exposed to ajowan, cinnamon, oregano, and thyme. Conclusions: Ajowan, cinnamon, oregano, and thyme were the most effective biofilm-degrading and -inhibitory EOs.