Effects of Compounds in Olea europaea on Growth of Major Enteric Bacterial Pathogens and Lactobacillus Strains

Introduction: The olive Olea europaea is rich in phenolic compounds and tri-terpenoids, both of which are associated with multiple promising pharmacological activities including anti-oxidant, anti-inflammatory, antimicrobial, and antiviral effects. Due to the growing multi-drug resistant foodborne bacterial pathogens, alternative antimicrobials are essential. Bio-active compounds extracted from Olea europaea might be potential in reducing colonization of enteric bacterial pathogens as well as maintaining the growth of probiotics.

Purpose: The purpose of this study was to evaluate the antimicrobial property of 4 olive compounds, maslinic acid (MA), oleanolic acid (OA), hydroxytyrosol (HT), and oleuropein (OP), against major foodborne pathogens as well as their role on growth of Lactobacillus strains.

Methods: The minimum inhibitory concentration (MIC) of these 4 compounds on enterohemorrhagic E. coli EDL933 (EHEC), Salmonella Typhimurium LT2 (ST), and Listeria monocytogenes LM2 (LM) were determined by broth micro-dilution method. Growth conditions of Lactobacillus casei (LC), L. rhamnosus (LR), and L. plantarum (LP) were determined in MRS broth with and without 1% MA, OA, HT, or OP. Data were analyzed using ANOVA.

Results: The MIC of HT on EHEC, ST, and LM was found to be less than 0.125% (w/v), and the MIC of OP on EHEC, ST, and LM was showed to be 2%, 1%, and 0.5%, respectively. However, the MIC of MA or OA on three foodborne pathogens was found to be higher than 4%. Growth of LC, LR, and LP were stimulated by ≈0.5, ≈1.0, and ≈1.0 logs with 2% MA and by ≈1.0, ≈1.0, and ≈0.5 logs with 2% OA at 24 h. Two percent OP maintained the growth of Lactobacillus, whereas 2% HT exhibited inhibitory effects on them.

Significance: HT in olive could be a potential alternative antibiotic; OP, both showed antimicrobial effect and maintained in probiotic growth, and may aid in prevention of foodborne illness.