How to Determine the Antimicrobial Activity of Plant Extracts
The primary purpose of determining the antimicrobial activity of plant extracts is to determine their bioavailability and the composition of plant materials. The polarity of plant compounds may be a factor in the antimicrobial activity of plant extracts. However, the nonpolarity of plant compounds will not diffuse as well as the polar compounds and will therefore have lesser antimicrobial activity. There are several ways to determine the antimicrobial activity of plant extracts.
Variability of antimicrobial activity
While the antimicrobial activity of different plant extracts was often similar, variations were also seen. Interestingly, some species exhibited different antimicrobial activity in separate experiments. The most potent antimicrobial activity was seen for Melaleuca fulgens, while other plants had lower antimicrobial activity. The MIC values of some of the plant extracts were eight to twenty times lower than the highest performing species, M. fulgens.
To study the antimicrobial activity of plant extracts, methanolic plant extracts were collected and streaked onto BHI. These extracts were incubated at 35 deg C for 24 h to determine their antimicrobial activity. Plant extracts were then diluted in Mueller-Hinton broth (supplied by Oxoid, UK).
For the antibacterial tests, A. Americana crude extract yields were sufficient, even after dried leaves. The crude extract yields are shown in Table 2, and the percentage yields of different fractions are shown in Table 3. The antimicrobial effects of the chloroform, acetone and petroleum ether extracts are summarized in Tables 4 and 5. MIC values of the various plant extracts were determined by subtracting the weight of the fine material present in the original vessel.
Studies have shown that essential oils from plants such as the Mentha family are active against bacteria. Several essential oils have been isolated and characterized for their antimicrobial and antioxidant activities. Some essential oils have multiple antimicrobial effects and are helpful for various applications, including the food industry and confectionery. The essential oils were obtained from different locations, including Italy and Slovakia. GC/MS and disc diffusion methods were used to identify dominant compounds. The antibacterial activity was estimated using a broth microdilution technique.
Antibacterial activity of R. chalepensis essential oil was assessed against seven strains of bacteria using the agar disk diffusion method. The essential oil produced similar antibacterial effects against both Gram-positive and Gram-negative bacteria. However, the antimicrobial activity was more significant for Agave americana at higher concentrations than gentamycin. The antibacterial activity of r. chalepensis essential oil was comparable to gentamycin, while a lower concentration of the plant’s extract did not produce any microbial activity against Gram-negative bacteria.
Contributions to antimicrobial assays
To investigate the role of plant extracts in the development of antimicrobial assays, we used an agar healthy diffusion method to evaluate the activity of several plant products. The MICs were prepared by flooding nutrient agar plates with 1.5 X 108 bacteria/ml of a particular bacterial strain or 105 spores/ml of a fungus suspension. A cork-borer was used to boreholes in the agar. The agar was then incubated at 37 deg C for 24 h. We then measured the percentage extract yield and compared it with the control.
To monitor the antimicrobial activity of the various plant extracts, we performed an agar well diffusion assay with positive controls (Streptomycin sulfate) and negative control (normal saline). This study revealed that Syzygium aromaticum and C. Sinensis had high antimicrobial activity, while M. Piperita showed only weak antimicrobial activity. Furthermore, methanolic plant extracts were more effective in inhibiting bacteria than aqueous plant extracts. We also observed that R. nepalensis and P. dodecandra were more potent against the reference Salmonella strains, while G. ferruginea leaves had the lowest.
Phytochemical screenings of the plants were carried out based on qualitative methods. We identified the constituents based on their antimicrobial activity by comparing the intensity of their color. The shadier the color, the more engaged the plant is against antimicrobial organisms. However, the current study results are still preliminary, and more studies are necessary. The study findings suggest that plant extracts are promising sources of commercial antimicrobial agents.
In the present study, five plants used in traditional healthcare in West Africa were selected. These plants were screened for phytochemicals in aqueous and ethanol extracts against two microbial strains of Proteus mirabilis and Pseudomonas aerobiosis. The antimicrobial activity was determined by comparing the plant extracts against chloramphenicol or griseofulvin as positive controls.
The results from the current study also suggest that Tunisian plants have antibacterial activity. The medicinal plant crude extracts screening revealed that these plant species are rich sources of antibacterial agents. The authors acknowledge Professor Rachid Chemli and Mr. Mohamed Ben Salah for their assistance in the study. They also thank Lilia Trabelsi, Miss Dalila Haouas, and Institut Superieur Agronomique de Chott-Meriem for their assistance.
Methods used to determine the zone of inhibition.
In vitro tests to determine the antimicrobial activity of plant extracts were conducted using agar plates inoculated with a standardized inoculum of the test microorganism. Discs containing the test compound were placed on the agar and incubated for 24 h under suitable conditions. During the test, the antimicrobial agent diffused into the agar and inhibited the germination of the test organisms. To confirm the effectiveness of the test, three replicates were carried out for each organism tested.
Ethanol and ethanolic extracts of several plant species were tested. Ethanol had the highest inhibition zone against the most sensitive Gram? Harmful bacteria, P. mirabilis, while the lowest inhibition zone was observed with water extract of thyme. These results indicated that plant extracts had different modes of action against the test organisms. In addition, the antimicrobial activity of plant extracts was unaffected by antibiotic resistance.
Aloe vera and neem ethanol extracts inhibited the growth of MRSA and S. aureus. The presence of flavonoids and saponins in the plant extracts could explain this activity. Furthermore, the presence of tannins was found to be responsible for this antimicrobial activity, which Hatano et al. have reported.
The results obtained from these studies could be helpful in the development of new antimicrobial products and in combating multidrug-resistant bacteria. The findings of these tests should be reliable and comparable with those of phytochemical studies. Furthermore, antimicrobial testing should not be used to supplement phytochemical studies. If a plant extract is suspected of exhibiting antimicrobial activity, it should be evaluated by antimicrobial tests.
Methods used to determine MICs.
A variety of methods exist for determining the MICs of plant extracts. The MIC is the minimum concentration of a plant extract that inhibits the growth of an organism. These methods vary widely in their methodological aspects. Some methods rely on dilution and diffusion, whereas others use antimicrobial gradients. An increasing concentration gradient is applied to a strip and deposited on a previously inoculated agar surface in antimicrobial gradient methods.
In one study, Epaltes divaricate, an invasive fungus, gave a MIC of 0.48 mg/ml against S. aureus when diluted seven times in Mueller-Hinton broth. The plant extract’s turbidity was adjusted to the McFarland turbidity standard. In the following study, a concentration of 50 mg/ml of a bacterial recess was counted in each well, except for the negative control. The positive control was a Cefotaxime IV drug, while the negative control was the plant extract alone. The antimicrobial action was confined by measuring the bacterial growth at a wavelength of 630 nm.
Another study showed that ethanolic and water extracts of clove and thyme were antifungal. Both of these extracts inhibited CA growth. Cells exposed to these extracts significantly reduced cytoplasmic pH and cell wall disruption. These results are compatible with those obtained by ethanolic and aqueous extracts of these plants. These results have implications for food safety and natural antimicrobials’ efficacy.
EC and SA are the two most widely used methods for determining the MICs of plant extracts. These tests require exact evaluations and can be compared to determine the MICs of a plant extract. The MICs of plant extracts are the best way to test the efficacy of a particular plant. MICs can be determined using various methods and are crucial for effective antibacterial research.
Agar well diffusion is another technique for determining plant extracts’ minimum inhibitory concentrations (MICs). The culture media used for this test must be pH-balanced and contain a minimum concentration of a particular antimicrobial agent. The MICs of a plant extract should be a concentration of at least one milligram per milligram of antimicrobial activity.