Colorado State Discovers Compound in Sweet Basil that Kills Bacteria Responsible for Fatal Lung Infections, Plant Diseases

Colorado State University horticulture researchers have discovered in laboratory settings that an antioxidant found in sweet basil kills pathogen cells that cause serious and often fatal lung infections in cystic fibrosis patients.

The compound, known as rosmarinic acid, kills Pseudomonas aeruginosa, bacteria that causes infections in people with compromised immune systems, and also particularly in people with cystic fibrosis. The compound, common in the environment and also found in herbs related to sweet basil including rosemary and catnip, is known for its antioxidant properties and is one reason why sweet basil is promoted as a healthy herb.

"This discovery means that rosmarinic acid has beneficial antimicrobial properties as well as antioxidant properties," said Jorge Vivanco, horticulture professor and the lead researcher on the project. Research also was conducted by Colorado State post-doctoral researcher Harsh Pal Bais, graduate student Travis Walker and microbiology Professor Herbert Schweizer.

In the experiment, Colorado State researchers found that the acid, which has previously been known to exist in sweet basil leaves, also is secreted from roots of sweet basil plants when the roots are close to P. aeruginosa bacteria cells and other fungi and bacteria.

P. aeruginosa bacteria commonly exists and grows in soil and water and, in addition to causing lung, wound and blood infections in humans and animals, can cause bacterial diseases in plants. The study shows that rosmarinic acid acts as an antifungal and antibacterial chemical against an array of pathogens that commonly are found in the environment and that affect plants. The acid might be an environmentally friendly, chemical-free solution against some bacterial diseases in plants if it is sprayed directly onto the infected area. If this compound proves effective, it may reduce the amount of chemicals used to treat some plant diseases.

In the study, rosmarinic acid killed individual P. aeruginosa cells, but when growing in lungs, the bacteria cells function in groups that are surrounded by a light coating, called a biofilm. Vivanco believes that the findings suggest that rosmarinic acid may be effective against P. aeruginosa infections and against bacterial infections in plants, but further research should be performed under more realistic conditions. For example, additional studies at Colorado State are looking at how effective rosmarinic acid is against P. aeruginosa cells surrounded by biofilm.

Results of future studies could have a considerable positive impact on health, horticulture and agricultural industries because of potential for medicinal benefits, fungicide applications and an additional market for basil crops.

Vivanco points out that levels of rosmarinic acid are actually higher in the leaves and stems than the roots of sweet basil, which may mean that eating the herb provides rosmarinic acid and expands the health benefits of sweet basil by providing antimicrobial benefits in addition to the antioxidant benefits already known to exist.

In addition to plaguing people with cystic fibrosis, P. aeruginosa lung infections are common in burn victims, cancer patients or others with compromised immune systems. The infections are usually treated with antibiotics, but with mixed success.

Chronic bacterial lung infections are almost inevitable in people with cystic fibrosis. The disease causes a thick mucus that clogs the lungs, and P. aeruginosa bacteria thrives in that mucus. Cross-infection among patients is common. Patients often become resistant or allergic to antibiotics and the effectiveness of the antibiotics against lung infections decreases along with their lung function. Most people with cystic fibrosis die from lung damage caused by recurrent lung infections, and P. aeruginosa lung infections are the most common, according to the National Institute of Health.

Bacterial diseases plague ornamental and vegetable plants under the right conditions. The diseases decrease commercial yields and the productivity of private gardens and typically are treated with chemical fungicides, which may be harmful to the environment.

The study was published in the November issue of Plant Physiology and Biochemistry.

The group will continue to study the effects of the compound on lung infections and plant diseases in future studies.