Combinatorial effect of probiotics and some medicinal oils on pathogenic bacteria

Abstract

Probiotics (PB) and medicinal oils (MO) have beneficial effects against microbial gut infections. The present study aimed to evaluate the in vitro combined antibacterial activities of PB and MO against pathogenic strains. Antibacterial activities of three probiotic strains (Lactobacillus plantarum, Lactobacillus casei, and Lactobacillus acidophilus) and five MO (Bitter almond, Clove, Eucalyptus, Peppermint and Thyme oils) were investigated using agar well diffusion method. Cell-free supernatant (CFS) from PB combined with MO showed antagonistic effects against most of the tested pathogenic strains. Thyme and clove oils showed the highest activity. The combinations of CFS from PB and MO were tested by agar well diffusion method. These combinations showed synergistic activity against the S. aureus especially combinations containing clove, peppermint and thyme oils. Combinations were investigated also by Checkerboard dilution method. Most of CSF significantly lowered the minimum inhibitory concentrations (MICs) of MO against the tested bacteria and fractional inhibitory concentration indices (FICIs) for these combinations ranged from 0.12 to 0.75. Most of the tested CFS-MO combinations showed marked synergistic activity against S. aureus, E.coli and K. pneumoniae. In a conclusion, in vitro antibacterial study for CFS-MO combinations in our ongoing work suggests the possibility of using these combinations in clinical urinary and gastrointestinal tract infections.