Garlic blocks quorum sensing and promotes rapid clearing of pulmonary Pseudomonas aeruginosa infections

Abstract

The opportunistic human pathogen Pseudomonas aeruginosa is the predominant micro-organism of chronic lung infections in cystic fibrosis patients. P. aeruginosa colonizes the lungs by forming biofilm microcolonies throughout the lung. Quorum sensing (QS) renders the biofilm bacteria highly tolerant to otherwise lethal doses of antibiotics, and protects against the bactericidal activity of polymorphonuclear leukocytes (PMNs). It has been previously demonstrated that QS is inhibited by garlic extract. In this study, the synergistic effects of garlic and tobramycin, and PMNs activities have been evaluated. P. aeruginosa was grown in vitro in continuous-culture once-through flow chambers with and without garlic extract. The garlic-treated biofilms were susceptible to both tobramycin and PMN grazing. Furthermore, the PMNs showed an increase in respiratory burst activation, when incubated with the garlic-treated biofilm. Garlic extract was administered as treatment for a mouse pulmonary infection model. Mice were treated with garlic extract or placebo for 7 days, with the initial 2 days being prophylactic before P. aeruginosa was instilled in the left lung of the mice. Bacteriology, mortality, histopathology and cytokine production were used as indicators. The garlic treatment initially provoked a higher degree of inflammation, and significantly improved clearing of the infecting bacteria. The results indicate that a QS-inhibitory extract of garlic renders P. aeruginosa sensitive to tobramycin, respiratory burst and phagocytosis by PMNs, as well as leading to an improved outcome of pulmonary infections.

In vivo Safety of Dichloromethane-Methanolic Extract of Allium sativum in Normal Mice

“…This is in line with the findings reported by Sumiyoshi and Bjarnsholt et al [26,27] that A. sativum is a stimulator of the immune functions in rats.…”

Inhibition of quorum sensing in Chromobacterium violaceum by Syzygium cumini L. and Pimenta dioica L.

“…Fresh garlic extract having strong anti-QS activity, injected subcutaneously for 7 d [1.5% of the mass of the mouse (20 g)] promoted rapid clearing of pulmonary P. aeruginosa infections [8] . Oral treatment with a fresh garlic extract for 14 d significantly lowered renal tissue destruction by anti-QS activity against P. aeruginosa infections in the mouse urinary tract infection model [22] .…”

“…However, the mode of action of many phytocompounds against the target organism is not clearly understood. Recent research has revealed that a few natural products including plant extracts have properties for modulating bacterial QS system, thereby reducing the virulence [8,9] . Syzygium cumini (S. cumini) and Pimenta dioica (P. dioica) are widely used medicinal plants having ability to alleviate bacterial infections and are used in traditional healing in different parts of the world.…”

Exploiting Quorum Sensing To Confuse Bacterial Pathogens

“…Extracts of fruits (e.g., blackberries, cranberries, vanilla, and citrus) and herbs (e.g., rosemary and turmeric) and extracts and oils of other plant materials (garlic, clove, and cinnamon) and medicinal plants (e.g., betel nut and notoginsing) have all displayed QSI activity to some degree, typically found via inhibition of violacein production in the C. violaceum bioassay (137,138,(264)(265)(266)(267)(268)(269)(270)(271)(272)(273)(274)(275). In very few cases, however, have individual compounds been isolated or identified from these kinds of complex sources.…”