Rosemary herb is an effective antimicrobial agent against a wide range of bacteria in laboratory media. Antimicrobial activity of rosemary oil has been documented against moulds, and G^- and G⁺ bacteria.

Antimicrobial properties of alcoholic (ethanol) extracts of Rosmarinus officinalis with 70%, 80% and 90% of ethanol were examined. Diffusion method for monitoring antimicrobial activity in inoculated plates was used. Examined alcoholic extract were applied directly onto the disc as well as those dissolved in polyethylene glycol. Microorganisms, which were used as test, are: Bacillus subtilis, Staphylococcus aureus, Pseudomonas aeruginosa, Esherichia coli, Aspergillus niger and Candida albicans.

Alcoholic extract of Rosemary showed strong antimicrobial activity on all tested microorganisms except C. albicans. The strongest antimicrobial activity was against Staphylococcus aureus. In addition to bactericidal effect against Bacillus subtilis and Staphylococcus aures, outstanding bacteriostatic effects exist. The results presented in our study show that extracts of Rosemary also possess lower, but measurable antifungal activity against Aspergilus niger.