Carvacrol inhibits biofilm formation and production of extracellular polymeric substances of Pectobacterium carotovorum subsp. carotovorum

Pectobacterium carotovorum causes soft rot in plant food due to its ability to synthesize exoenzymes, and secrete polymeric substances to form biofilm; in addition, this aggregated form of bacteria creates resistance during disinfection. However, the biofilm formation process and composition of P. carotovorum is still uncharacterized, which is important to design more efficient disinfection procedures. Among the actual disinfection trends, the use of plant compounds has deserved plenty of attention; being carvacrol, a monoterpene constituent of oregano essential oil that is known to reduce biofilm formation of many bacteria. Therefore, the objective of this study was to evaluate the effect of carvacrol against biofilm development of P. carotovorum, EPS composition, bacterial surface charge, adhesion potential and motility. Minimal planktonic inhibitory and bactericidal concentrations of carvacrol were 2.66 and 3.99 mM; whereas, concentrations of 1.33 and 3.99 mM were needed to inhibit and eradicate biofilm, respectively. Carvacrol at 0.66 mM was chosen as the concentration to evaluate its effect on EPS secretion, motility and surface physicochemical characteristics without affecting the viability of planktonic cells. It was shown that carvacrol at this concentration decreased bacterial surface charge (−2.15 mV), adhesion potential (−1.5 mJ/m2) and swimming motility of P. carotovorum (48.2 mm) compared with untreated bacteria. In addition, polysaccharides were the main components of the biofilm matrix of P. carotovorum, whose synthesis was inhibited by the presence of carvacrol. These results demonstrated that carvacrol could be effective against P. carotovorum biofilm formation and eradication, reducing adhesion, motility and synthesis of polysaccharides.