Chemical Composition, Antibacterial and Antibiofilm Actions of Oregano (Origanum vulgare subsp. hirtum) Essential Oil against Salmonella Typhimurium and Listeria monocytogenes

Abstract

Essential oils (EOs) are plant mixtures that are known to present strong bioactivities, including a wide antimicrobial action. Biofilms are microbial sessile structures that represent the default mode of growth of microorganisms in most environments. This study focused on the antimicrobial action of the EO extracted from one of the most representative oregano species, that is, Origanum vulgare (subsp. hirtum), against two important foodborne pathogens, Salmonella enterica (serovar Typhimurium) and Listeria monocytogenes. For this, the minimum inhibitory concentrations of the EO against the planktonic and biofilm growth of each bacterium were determined (MICs, MBICs), together with the minimum bactericidal and biofilm eradication concentrations (MBCs, MBECs). The EO was also analyzed for its chemical composition by gas chromatography—mass spectrometry analysis (GC-MS). The influence of EO exposure on the expression of some important virulence genes (hly, inlA, inlB and prfA) was also studied in L. monocytogenes. Results revealed a strong antibacterial and antibiofilm action with MICs and MBICs ranging from 0.03% to 0.06% (v/v) and from 0.06% to 0.13% (v/v), respectively. The application of the EO at 6.25% (v/v) for 15 min resulted in the total eradication of the biofilm cells of both pathogens. The EO was mainly composed of thymol, p-cymene, γ-terpinene and carvacrol. The 3 h exposure of L. monocytogenes planktonic cells to the EO at its MBIC (0.06% v/v) resulted in the significant downregulation of all the studied genes (p < 0.05). To sum, the results obtained advocate for the further exploitation of the antimicrobial action of oregano EO in food and health applications.

Essential Oils from Southern Italian Aromatic Plants Synergize with Antibiotics against Escherichia coli, Pseudomonas aeruginosa and Enterococcus faecalis Cell Growth and Biofilm Formation

“…Among the EOs analyzed, EO from O. vulgare exhibited the highest antimicrobial activity in both E. coli and E. faecalis (MIC = 1.25 mg/mL), confirming the results of two of our previous studies [8,11]. This result is also in line with literature data in which the antimicrobial efficacy of this EO was demonstrated by the low MIC values determined not only with respect to the above bacteria but also with others such as S. aureus, Salmonella enteritidis, Salmonella Typhimurium, Listeria monocytogenes, and Bacillus subtilis [30][31][32][33][34][35][36]. Interestingly, this EO is the only one that, in the conditions we adopted, inhibits bacterial growth in P. aeruginosa.…”

Oregano Essential Oil in Livestock and Veterinary Medicine

“…This inhibitory effect is observed even at extremely low concentrations, effectively impeding the formation of pathogenic biofilms. The present investigation demonstrated that Greek oregano possesses a robust antimicrobial efficacy comparable to, or potentially surpassing, that of oregano sourced from other countries, as previously reported [ 67 ]. In their study, Rupasinghe et al evaluated the mechanism by which carvacrol inhibits Streptococcus pyogenes biofilms [ 68 ].…”

Mediterranean Plants with Antimicrobial Activity against Staphylococcus aureus, a Meta-Analysis for Green Veterinary Pharmacology Applications

“…It is frequently used as a flavoring herb, feed addition, and garden adornment, but it also serves as a medicine since it possesses antibacterial, antioxidant, and anti-inflammatory effects [ 134 , 135 ]. Oregano has a wide range of uses in food preservation due to the abundance of its active ingredients, including carvacrol and thymol, but it also has a unique bacteriostatic action on Salmonella enteritidis [ 136 ], Cronobacter sakazakii [ 137 ], Escherichia coli [ 135 , 138 , 139 ], Staphylococcus aureus [ 135 ], and Listeria monocytogenes [ 140 , 141 ]. There are differences in the quantity and quality of oregano essential oil (OEO) from diverse germplasm sources.…”