Effect of essential oil from sage (Salvia fruticosa) on some microorganisms and on Salmonella typhimurium in a model milk system

The inhibitory effect of sage essential oil against 8 strains of Gram-negative bacteria and 4 strains of Gram- positive bacteria was studied. Preliminary screening of antimicrobial activity of sage oil was conducted using filter paper disc agar diffusion method. The minimal inhibitory concentration (MIC) of sage oil against various microorganisms was also measured. In general sage oil showed a moderate effect ( 28 to 16 mm zone of inhibition) against most Gramnegative bacteria and two Gram-positive bacteria with a strong effect against Shigella spp (inhibition zone = 28mm). MIC ranged from 3000ppm (Micrococcus spp.) to mote than 25,000 ppm. The effect of sage essential oil (0.3, 0.6 and 1%) on S. typhimurium (5.0 ± 0.1 log CFU/ml) in sterilized skimmed milk incubated at 30°C for 6 days was evaluated. Antimicrobial activity was lost after the first 24 hrs of incubation in milk allowing pathogen to proliferate and reach a maximum population of 6.5 and 6.9 log CFU/ml for milk samples containing 0.6 and 1% sage oil after 6 days respectively compared with 2.5 logs CFU/ml for control (0%). No synergistic effect on S. typhimurium (5.5 log CFU/ml) was reported when a combination of sage essential oil and lactic acid bacteria (1%) in cultured buttermilk incubated at 21°C for 72 hrs was tested. It seems that antimicrobial action of sage oil depends on food composition (protein) and nature of microorganisms.