Inhibition of some foodborne bacteria by alcohol extract of sumac (Rhus coriaria L.)

The inhibitory effect of alcohol extract of sumac (Rhus coriaria L.) was investigated at concentrations of 0.1, 0.5, 1.0, 2.5 and 5.0% (w/v) on the growth of 12 bacterial strains (6 Gram positives and 6 Gram negatives), mostly foodborne including pathogens. Minimal inhibitory concentration of the spice for each test organism was also studied by observing their growth on Nutrient Agar containing the spice extract at various incremental levels equivalent to 100-5000 mg/L of spice. Alcohol extract of sumac was found to be effective against all the test organisms, Gram positives being more sensitive than Gram negatives. Among the Gram positives, Bacillus species (B. cereus, B. megaterium, B. subtilis and B. thuringiensis) were found to be the most sensitive, surviving up to only 500 mg/L of the spice, followed by Staphylococcus aureus (1000 mg/L), whereas Listeria monocytogenes was found to be the most resistant, surviving up to 1500 mg/L. Of the Gram negative bacteria, Salmonella enteritidis and Escherichia coli type I were found to be more resistant, surviving up to 3000 mg/L of the spice, followed by E. coli O157:H7 (2500 mg/L), Hafnia alvei (2000 mg/L), Proteus vulgaris (1500 mg/L) and Citrobacter freundii (1000 mg/L). Significant differences (P < 0.01) were found among bacterial strains and between the extracts of unripened and ripened sumac samples, with ripened being more effective against all of the bacteria tested.