Pseudomonas aeruginosa tolerance to tobramycin, hydrogen peroxide and
polymorphonuclear leukocytes is quorum-sensing dependent.

http://www.ncbi.nlm.nih.gov/pubmed/15699188?ordinalpos=1&itool=EntrezSystem2.PEn
trez.Pubmed.Pubmed_ResultsPanel.Pubmed_DiscoveryPanel.Pubmed_Discovery_RA&linkpo
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Garlic blocks quorum sensing and promotes rapid clearing of pulmonary
Pseudomonas aeruginosa infections.
Bjarnsholt T, Jensen PØ, Rasmussen TB, Christophersen L, Calum H,
Hentzer M, Hougen HP, Rygaard J, Moser C, Eberl L, Høiby N, Givskov M.

Centre for Biomedical Microbiology, BioCentrum, Technical University
of Denmark, DK-2800 Lyngby, Denmark.

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.