The antimicrobial activity of Monarda fistulosa L. (Lamiaceae), very rich in thymol (Heinlich, 1977), was tested on the following 10 micro-organisms: Staphylococcus aureus, Staphylococcus aureus Oxford, Streptococcus pyogenes, Streptococcus viridans, Neisseria sicca, Streptococcus pneumoniae, Peptostreptococcus, Candida albicans, Geotrichum candidum and Bacillus subtilis.

Aquaous and water-ethanol extract of Monarda, as well as its essential oil, were tested. For the most representative micro-organisms minimal inhibitory concentrations (MIC) and contact times were also determined. The remarkable antimicrobial activity on Peptostreptococcus and anaerobe mixt flora of the tested salivary secretion, makes possible to use these extracts in pharmaceutical preparations with antiseptic effect for the mouth and throat wash.

Monarda fistulosa originated from the North America is not analysed and studied in details from the antimicrobial point of view. The content of a volatile oil rich in thymol (Heinlich, 1977) determined us to examine and to re-evaluate its possible therapeutic use in preparations.

The plant is cultivated in the medicinal and aromatic plants garden of the University of Medicine and Pharmacy, Targu-Mures. It is a big plant, up to 1-1.5 meters high. This culture is advantageous in comparison to other species that could serve as source for thymol.

Previous examinations showed a high antimicrobial activity of the species Lythrum salicaria and determined us to study also the associated extracts of these two species.

From the aerial plant parts (Monardae herba) aqueous extract has been prepared and concentrated until ratio herb to solvent of 1:1 is achieved (extractum fluidum). Such prepared extract is than tested for its antimicrobial activity on the following micro-organisms: Staphylococcus aureus [1], Staphylococcus aureus Oxford [2], Streptococcus pyogenes [3], Streptococcus viridans [4], Neisseria sicca [5], Streptococcus pneumoniae [6], Peptostrepto-coccus [7], Candida albicans [8], Geotrichum candidum [9] and Bacillus subtilis [10]. From the majority of strains suspensions in physiological serum in concentration of 3·10⁹ germs/ml were prepared. From the rest of tested microorganisms (Streptococcus pyogenes, Strepto-coccus viridans, Neisseria sicca and Streptococcus pneumoniae) suspensions, in the same solvent, in concentration of 3·10⁸ germs/ml were created. Suspensions of germs were prepared of cultures 18 hours old in physiological serum.

Growing of cultures has been achieved by the use of different media used for these purposes. For the strains [1]-[6] and [10] blood-agar medium is used, for strains [1], [2], [5] and [10] - culture medium, for strain [7] - nutrient agar with thiocolic acid and culture medium with thiocolic acid, while strains [8] and [9] were tested on solid and liquid Sabouraud medium.

The study of the antimicrobial effect was made both, on solid and liquid mediums, by the use of horizontal diffusiometric method.

In the case of liquid media, experiments were conducted with 5 ml of medium, containing 1%, 5% and 10% of active substance, using test tubes with the same medium, but without examined extract as control. The inoculation was achieved by adding of 0.1 ml germ suspension in concentration of 3·10⁸ germs/ml, or 3·10⁹ germs/ml, as it is already mentioned. Test tubes were put to incubation at 37°C for 18 hours and cultures were subsequently transferred on blood-agar medium and Sabouraud medium.

For diffusimetric method, microbial strains (suspensions in indicated concentrations) were transferred on the surface of the media. After drying, previously sterilised filter paper discs (Ć = 11 mm) were put on the surface of inoculated media. Tested extracts (0.02 ml) were applied to the discs and after pre-diffusion of 60 minutes, inoculated media with impregnated discs were incubated (18 hours at 37°C and 48 hours for fungi). At the end diameters of the inhibition zones were measured. The results are presented in the next table (Table 1).

Anti-microbial activity of the water-ethanol extracts of Lythrum and Monarda (1:1), alone or mixed in equal parts with essential oil of Monarda and the extract of Monarda without oil, were tested too. Results are presented in the next table (Table 2).

For determination of MIC, three microbial strains were selected. Test was conducted with concentration of indicated plant isolates in the liquid medium of 0.5%, 1.0%, 2.5%, 5.0% and 10.0%, by the use of previously described method. Results are presented in the next table (Table 3).

Antimicrobial activity of Monarda and Lythrum on the strain of Peptostreptococcus and on fresh saliva, which represents the mixt anaerobe flora, in dilution 1:10 000 was verified. In anaerobe medium (agar with thioglicolic acid) metallic cylinders with diameter of 6 mm were put and - in the left cavity, test solutions (0.1 and 0.2 ml). After 30 minutes whole surface was covered with the same anaerobe medium without micro-organisms. After solidify, the medium was treated with pirogalol, after the Beerens method, modified by Bittner.

1. The examination of the antimicrobian activity of the fluid extracts 1:1 of Monarda fistulosa and Lythrum salicaria, in concentrations of 1%; 5%; and 10%, in liquid media, showed that the highest effect was on the strain of Neisseria Sicca. Concentrations of 1% of both extracts inhibited totally the development of the micro-organism. The extract of Monarda was effective also on the Staphylococcus strains, especially on Staphylococcus aureus Oxford.

2. Comparing the aqueous extracts, water-ethanol extracts, essential oil and the extract of Monarda without oil, the most effective were water-ethanol extracts. Water-ethanol extract of Lythrum was more effective on the strains of Streptococcus pyogenes, Streptococcus pneumoniae, Candida albicans, Geotrichum candida and Bacillus subtilis. The water-ethanol extract of Monarda was less effective on Streptococcus pneumoniae, Candida albicans and Bacillus subtilis.

3. The essential oil of Monarda inhibated completely the development of all the strains of micro-organisms.

4. The mixture of extracts of Monarda, Lythrum and essential oil in concentrations of 1% inhibited completely developmant of the micro-organisms examined at the MIC, i.e. Staphylococcus aureus Oxford, Streptococcus pyogenes and Candida albicans.

5. Contact time for extracts of Monarda and Lythrum (aa), were determined too. Total inhibiting effect were determined as follows: 5 minutes for Candida albicans; 10 minutes for Staphylococcus aureus Oxford and 30 minutes for Streptococcus pyogenes.

6. The examined extracts of Monarda and Lythrum had a major antimicrobial activity, both, on the strains of Peptostreptococcus and on the mixt flora from the tested saliva.

Results obtained from the research of the antimicrobial activity of Monarda fistulosa and Lythrum salicaria extracts - showed effects which give the possibility to use these extracts in pharmaceutical preparations with antiseptic effect for the mouth and throat wash.

1. Rogosca M., Racz G. and Peter M. (1983): Antimicrobial activity of the associated extracts of Lythrum salicaria and Monarda fistulosa, Rev. Med., 2, 68-70.

2. Bitnner J. (1975):Simple method in order to realise the conditions of general anaerobiosis, Microbiol., 1, 55-57.

3. Heinlich G. (1977): Biochemie Physiol. Pflanz., 171,17.