The crude use of rhamnolipids an antibiotic dates back to before the common use of antibiotics when in 1899 R. Emmerich and D. Low reported the concentrated byproducts of Pseudomonas aeruginosa killed a number of other bacteria.
Biologically, rhamnolipids act in a number of ways. In microbiology, they help with the spreading of bacteria. They facilitate the bacterial metabolism of various compounds through emulsification. They protect certain bacteria and also kill or slow the reproduction of other bacteria, yeasts, and fungi.
Because rhamnolipids reduce surface tension and because they act as a surfactant, they help various bacteria and viruses disperse in a medium.
As a surfactant, rhamnolipids have the ability to emulsify compounds, which facilitates the access by some microorganisms to process or metabolize those compounds. This process has been used to advantage in bioremediation of some petrochemical contaminants. This process also allows some bacteria to grow in petrochemicals and waste. Pseudomonas aeruginosa and similar bacteria have often been isolated and studied from such petrochemicals.
Rhamnolipids have been demonstrated to destroy the outer wall of various fungi in the spore state (lysis of the zoospores.) This has proven to be an effective fungicide with numerous applications in agriculture, sanitation, and medicine.
Antibiotic – Antimicrobial – Bactericide
Rhamnolipids kill some bacteria. They also increase the susceptibility of certain gram-positive bacteria to specific antibiotics. Rhamnolipids can act as an anti-adhesive, inhibiting the ability of some bacteria to attach to a surface. Rhamnolipids will also inhibit the reproduction of certain bacteria and other cells. A number of studies have been done to determine the minimal inhibition concentration (MIC) on different bacteria and cells.
There is evidence that P. aeruginosa and other rhamnolipid-producing bacteria use low concentration of rhamnolipids to maintain open channels for nutrients in biofilms. These open channels keep the biofilm strong while at the same time the biofilm inhibits the effect of antibiotics.
In higher concentrations or on non-rhamnolipid producing bacteria the rhamnolipids seem to inhibit cell-to-cell interactions and the attachment of bacterial cells to a surface, thereby preventing the formation of the biofilm.
There is evidence that indicates that rhamnolipids stimulate and facilitate the detachment of bacteria from the biofilm into the planktonic form for dispersal to build new biofilms. When in the planktonic form, the bacteria are once again susceptible to antibiotics. It has also been discovered that the presence of rhamnolipids affects the motility of the planktonic bacteria.
Rhamnolipids in the right concentration are a hemolysin, meaning that they can break up red blood cells by lysis, destroying the blood cell wall.
Various studies have demonstrated that rhamnolipids help the treatment of numerous skin diseases such as psoriasis, lichen ruber planus, and neurodermatitis.
For skin wounds, rhamnolipids have been found to balance the growth of fibroblasts, keratinocytes and other skin cells during healing, preventing the contracting and scarring associated with skin healing. Studies have demonstrated accelerated full depth wound healing using rhamnolipids.
Rhamnolipids emulsifying properties, as well as antifungal and antibiotic properties help clear up acne.
There is some evidence that rhamnolipids help with immunosuppression withimmunomodulation and even immunorestoration.
Tests have shown rhamnolipids suppress the spread of breast cancer cells, although the minimum inhibitory concentration (MIC) at 6.25 ug/mL in one study may be too high for practical use. Research has shown promise combining rhamnolipids with other compounds to reduce the spread of cancer.
Cystic Fibrosis and Lung infections
Rhamnolipids have been implicated in the success of the opportunistic pathogen Pseudomonas aeruginosa infecting the lungs of cystic fibrosis patients. Normally bacterial invasion of the lungs in resisted by epithelia cells, but rhamnolipids help the infection of those cells. Since the alveoli of the lungs secrete and are lined by a pulmonary surfactant, the surfactant behavior of rhamnolipids may also interfere with their function.