The gram negative bacterium, Pseudomonas aeruginosa has the reputation of being an opportunistic multi-drug resistant pathogen, which is a cause of concern in pharmaceutical and healthcare settings. It plays a pivotal role in cystic fibrosis, where mucus clogged airways, hardened lungs, and dehydrated epithelial surfaces provide a suitable environment for its colonization and formation of thick biofilms, which in turn shield the microbes against antibiotic action, making them resistant. Release of toxins combined with colonization leads to down-regulation of the body’s immune system making it all the more difficult to be eradicated.
In a biofilm, bacteria commute with each other with the help of a density-dependent cell signal system referred to as “Quorum sensing.” It so happens that bacteria secrete these molecules known as autoinducers (AI) which, on reaching a critical cell density, bind to cytoplasmic receptors in the cells which is followed by dimerization, signal detection and binding to promoters of genes encoding for virulence factors, initiating their transcription. Pseudomonas aeruginosa has three such systems which release AI molecules (called N-Acylhomoserine lactones or ASL) which lead to production of toxins like alkaline protease, elastase, superoxide dismutase, lipopolysaccharides, rhamnolipids and efflux pumps. These contribute to their multidrug resistant nature.
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According to a recent press release by The University of Copenhagen, the compound Ajoene obtained from freshly ground garlic has been found to possess natural Quorum Sensing Inhibitory (QSI) properties. A study led by Tim Holm Jakobsen used this compound against artificially grown Pseudomonas aeruginosa biofilms in laboratory mice and found it to act synergistic-ally with antibiotics in successfully reducing the bacterial population. If earlier studies on this are taken into account, ajoene is a sulphur containing compound which has the ability to neutralize quorum sensing by enzymatically metabolizing the AI and blocking their signal detection pathways leading to weakening of the biofilm, wherein the antibiotics can exert the desired effects on the microbes. This combination can reduce virulence by as much as 90%. Some other health benefits of garlic (Ajoene) include reduction of blood pressure and serum cholesterol and providing relief in cardiovascular complexities. Garlic is also the storehouse of allicin, the world’s most powerful antioxidant (according to a report from Queen’s University, 2009). Some other naturally occurring QSIs include carrots, peas, chamomile, lemongrass and yellow peppers.
It should be noted that the amount of ajoene necessary to bring about the desired changes are equivalent to almost 50 bulbs of crushed garlic, which is not advisable for human consumption. Hence it is up to the pharmaceutical companies to utilize these gifts of Nature and make chemically modified compounds which can bring about the desired effects in very low concentrations. This would pave way for a healthier lifestyle and a longer lifespan.