Evaluation of the Antibacterial Activity of Origanum vulgare Aqueous Extracts Against Shiga Toxin-Producing Escherichia coli (STEC)

Oregano is an aromatic plant of the Mediterranean flora commonly used for medical purposes. In this study, the antibacterial activity of Origanum vulgare (oregano) aqueous extracts obtained by infusion (OEI) and decoction (OED) on cell viability and virulence gene expression of Shiga toxin-producing Escherichia coli O157:H7 (STEC), a known foodborne enteropathogen, was examined in planktonic and biofilm cultures. Results demonstrated antibacterial activity determined as minimum inhibitory concentration (MIC = 20 mg/ mL) and minimum bactericidal concentration (MBC = 80 mg/ mL) for both extracts. OEI and OED at subinhibitory concentrations (10 mg/mL) produced significant decrease of viable counts in both planktonic and biofilm cultures. OEI significantly reduced the transcription of stx1 (in planktonic culture), stx2, eae and ompA (in biofilm) genes, while OED reduced significantly the transcription of stx1, stx2, eae (in planktonic culture) and ompA (in biofilm) genes. OEI and OED demonstrated potential as antimicrobial agents to control STEC.