Related Experiment Videos
[Selective effect of propolis in the isolation of Listeria monocytogenes (author's transl)]
Abstract:
Propolis is a substance produced by honeybees. It is inhibitory to some bacteria species, mainly Gram-positive bacteria, but less inhibitory to Listeria monocytogenes (L.m) than to the other Gram-positive bacteria tested. In order to obtain selective growth of L.m. from contaminated samples, the effect of propolis in plating media and broths on various strains of bacteria was examined. Table I shows the effect of increasing concentrations of propolis in tryptose-agar (TA). L.m. tolerated higher concentrations of propolis than Streptococcus viridans and Staphylococcus aureus. L.m. grew well in tryptosebroth (TB) that contained 0.15 mg propolis pr. ml medium, while Streptococcus viridans and Streptococcus agalactiae were completely inhibited as seen in Table II. Table III shows that when serum was added to the agar, the inhibitory effect was reduced. It can also be seen that Gram-negative bacteria grew quite well on media that contained 0.19 mg propolis pr. ml. To reduce the growth of Gram-negative bacteria, nalidixic acid was added to the medium. Table IV illustrates growth of various species of bacteria in tryptosephosphatebroth (TFB) with or without propolis and nalidixic acid. Most of the strains tested were inhibited, but Pseudomonas aeruginosa and to some extent faecal streptococci were able to grow in the medium that contained the selective substances. As a conclusion it seems that propolis may be a valuable additive to a medium for the selective isolation of L.m.
Insights
Propolis, a bee product, shows selective inhibition against Gram-positive bacteria. This makes propolis a potential additive for isolating Listeria monocytogenes (L.m.) from contaminated samples.
Area of Science:
- Microbiology
- Natural Products Chemistry
Background:
- Propolis, a resinous mixture collected by honeybees, possesses antimicrobial properties.
- Its inhibitory effects vary among bacterial species, notably showing less inhibition against Listeria monocytogenes (L.m.) compared to other Gram-positive bacteria.
Purpose of the Study:
- To evaluate the efficacy of propolis as a selective agent in culture media for the isolation of Listeria monocytogenes (L.m.).
Main Methods:
- Investigated the effect of varying propolis concentrations on bacterial growth in different media (tryptose-agar, tryptose-broth, tryptose-phosphate-broth).
- Assessed the impact of nalidixic acid in combination with propolis to further enhance selectivity.
- Examined the influence of serum on the inhibitory activity of propolis.
Main Results:
- Listeria monocytogenes (L.m.) tolerated higher propolis concentrations than Streptococcus viridans and Staphylococcus aureus.
- Propolis at 0.15 mg/ml selectively inhibited Streptococcus viridans and Streptococcus agalactiae while allowing L.m. growth.
- Serum reduced propolis's inhibitory effect, while Gram-negative bacteria showed tolerance to 0.19 mg/ml propolis.
- Addition of nalidixic acid improved selectivity, though Pseudomonas aeruginosa and faecal streptococci exhibited some growth.
Conclusions:
- Propolis demonstrates potential as a valuable component in culture media for the selective isolation of Listeria monocytogenes (L.m.).
- Combinations of propolis with other agents like nalidixic acid may further optimize selective isolation protocols.