Can pairing conventional antifungal medicines with natural, edible compounds from plants such as thymol, extracted from the popular herb thyme, boost the healing effects of some of these drugs?
COMBINING natural products such as thyme and prescription drugs has been shown to be more effective in fighting severe fungal infections.
Agriculture-based, food-safety-focused studies by United States Department of Agriculture (USDA) scientists and their colleagues found that pairing conventional antifungal medicines with natural, edible compounds from plants such as thymol, extracted from the popular herb thyme, can boost the healing effects of some of these drugs.
Petri-dish experiments on the effect of combining thyme and conventional antifungal drugs on the fungus Aspergillus spp was conducted by now-retired Agricultural Research Service (ARS) research leader Bruce C. Campbell, ARS molecular biologist Jong H. Kim, and their co-investigators. ARS is the chief intramural scientific research agency of USDA.
The study was published in Annals of Clinical Microbiology and Antimicrobials.
Botanically called Thymus vulgaris, thyme is a medicinal plant, which grows in the humid tropical secondary forests of Africa. Thyme is a spice of choice in most kitchens in Nigeria. But it is also among several natural products used by traditional healers in Western Nigeria to treat a number of bacterial infections.
Phytochemical screening of the leaves revealed the presence of tannins, phlobatannins, flavonoids, steroids, terpenoids, saponins and cardiac glycosides, which are the most important bioactive constituents of medicinal plants.
Earlier study by Nigerian researchers, published in Journal of Medicinal Plants Research, concluded: “Results obtained in this study indicated that Cajanus cajan (pigeon pea), Riccinus communis (castor bean) and Thymus vulgaris (thyme) all contain bioactive medicinal principles which account for their inhibitory actions against the bacteria tested.
“Thymus vulgaris appears to be the most active as it inhibited seven out of the eight bacteria. Oral administration of the leaf extracts of the herbs at the concentration tested is safe as they did not cause significant alteration in cellular activities of the experimental animals.”
Meanwhile, Campbell and Kim’s work at the ARS Western Regional Research Center in Albany, California, United States, with species of Aspergillus mold, for example, has attracted the attention of medical and public health researchers. Found worldwide in air and soil, Aspergillus can infect corn, cotton, pistachios, almonds and other crops, and can produce aflatoxin, a natural carcinogen.
Aflatoxin-contaminated crops must be identified and removed from the processing stream, at times resulting in large economic losses. Since 2004, Campbell, Kim, and colleagues have carefully built a portfolio of potent, plant-based compounds that kill a target Aspergillus species, A. flavus, or thwart its ability to produce aflatoxin.
Further research and testing might enable tomorrow’s growers to team the best of these natural compounds with agricultural fungicides that today are uneconomical to use, according to Kim.
A. flavus and two of its relatives, A. fumigatus and A. terreus, may impact the health of immune-compromised individuals exposed to the fungus in moldy homes.
In a 2010 article in Fungal Biology, the team reported that thymol, when used in laboratory tests with two systemic antifungal medications, inhibited growth of these fungi at much lower-than-normal doses of the drugs.
A related study provided new evidence to support earlier findings, at Albany and elsewhere, which had suggested that plant compounds such as thymol might sabotage a target fungi’s ability to recover from oxidative stress triggered by antifungal drugs. A 2011 article published by Kim, Campbell and others in Annals of Clinical Microbiology and Antimicrobials documents this research.
Using plant-derived compounds to treat fungal infections is not a new idea, nor is that of pairing the compounds with antifungal medicines. But the Albany team’s studies have explored some apparently unique pairs, and have provided some of the newest, most detailed information about the mechanisms likely responsible for the impact of powerful combinations of drugs and natural plant compounds.
According to the Nigeria study published in Journal of Medicinal Plants Research, decoctions of the leaves were believed to have chemical components, which are active against pathogenic microorganism.
The study titled: “Studies on Medicinal and Toxicological properties of Cajanus cajan, Ricinus communis and Thymus vulgaris Leaf Extracts,” was researchers from Department of Biochemistry, Osun State University, Osogbo, Osun State and Departments of Biological Sciences and Chemistry, Bowen University, Iwo, Osun State.
Antimicrobial testing against eight pathogenic bacteria showed that all the extracts possess antimicrobial properties with Thymus vulgaris being the most effective as it inhibited seven out of the eight bacteria tested.
The extracts were tested against eight major bacteria namely: Staphylococcus aureus, Escherichia coli, Salmonella, Bacillus subtilis, Citrobacter, Proteus vulgaris, Pseudomonas and Micrococcus spp using the broth dilution assay procedure.
Thymol has been shown to have therapeutic effect on the lungs as ingesting or inhaling the oil helps to loosen phlegm and relax the muscles in the respiratory tract.
In Germany, concoctions of thyme are frequently prescribed for coughs, including those resulting from whooping cough, bronchitis and emphysema. Thyme extract was included in a popular cough syrup, Pertussin, that is no longer on the market.
Because of its proven antimicrobial activities, thyme is used in herbal teas prepared for colds and flus. In addition, thyme has been shown to have antifungal properties and could be used against athlete’s foot.
Until now, a solution of thyme’s most active ingredient, thymol, is used in such over-the-counter products as Listerine mouthwash and Vicks VapoRub because of its well-known antibacterial and antifungal properties.
Meanwhile, scientists from Leeds Metropolitan University tested the effectiveness of thyme, marigold and myrrh tinctures at killing the acne-causing bacterium and compared it with that of benzoyl peroxide, used in acne creams. The tinctures were prepared by steeping the herbs in alcohol.
The scientists used a standard in vitro model, commonly used to test the effect of different substances applied to the skin. This included an alcohol control to ensure that any antibacterial action was not due to the sterilising effect of the alcohol in the tincture.
While all the herbal tinctures were able to kill the bacterium after five minutes of exposure, that of thyme was the most effective, the researchers said.
They also found that the thyme tincture had a greater antibacterial effect than standard concentrations of benzoyl peroxide, the active ingredient in most anti-acne creams and washes.
