Anti-Bacillus and Anti-Shigella Activities of the Essential Oil from Perilla fruescens var. japonica Hara

Abstract

To develop new effective and safe natural antibiotics against antibiotic-resistant food-borne pathogenic bacteria, the essential oil was extracted from the leaves of Perilla frutescens var. japonica Hara. Its composition was analyzed by GC-MS and its activities were tested against antibiotic-susceptible and resistant strains of some food-borne bacteria that can cause severe clinical symptoms in humans and animals. In addition, we determined the capacity of this oil to modulate the resistance of Bacillus and Shigella to antibiotics by checkerboard-titer tests on the basis of their MICs (minimum inhibitory concentrations). The essential oil fraction of P. frutescens var. japonica and its main component, perilla ketone, showed significant inhibitory activity against most of the tested strains of antibiotic-susceptible and resistant bacteria, resulting in MICs ranging from 0.25 to >2.00 mg/ml. The Perilla oils combined with norfloxacin or trimethoprim/ sulfamethoxazole showed synergistic or additive effects against Bacillus and Shigella species with FICIs ranging from 0.09 to 1.00 in the checkerboard-titer tests. In addition, the Perilla essential oil fraction and perilla ketone exhibited antioxidant activity with IC50s of 55.45 mg/ml and 71.13 mg/ml, respectively, in DPPH scavenging evaluation tests. Therefore, the essential oil fraction of P. frutescens var. japonica and its main component could be useful agents in the treatment of Bacillus and Shigella infections and as safe additives in food materials to prevent contaminations by these bacteria, especially in the face of the rapid increase of antibiotic-resistant strains, which can cause severe symptoms in humans. In addition, the significant antioxidant activity of this oil fraction or perilla ketone could provide benefits when applied as food preservatives.