Quorum Sensing Inhibition in Chromobacterium violaceum by Amikacin Combination with Activated Charcoal or Small Plant-Derived Molecules (Pyrogallol and Coumarin)

The study was aimed at effective inhibition of quorum sensing (QS) in the model bacterium Chromobacterium violaceum ATCC 31532 by combinations of compounds with different anti-QS activity mechanisms. These mechanisms were: (1) suppression of autoinducer (C-6-AHL) biosynthesis by subinhibitory concentrations of an aminoglycoside antibiotic amikacin; (2) sorption of synthesized C-6-AHL on activated charcoal particles; and (3) decreasing the bacterial cells sensitivity to the autoinducer by low-molecular weight compounds of plant origin: pyrogallol or coumarin. Simultaneous presence of amikacin and activated charcoal in the cultivation medium paradoxically decreased their combined anti-QS activity due to partial binding of the antibiotic to the sorbent particles, while two-step use of first the antibiotic and then the sorbent led to an additive effect due to sequential decrease the of C-6-AHL extracellular concentration. Amikacin combinations with pyrogallol or coumarin resulted in a expressed anti-QS effect, with evidence of superadditivity showed by isobolographic analysis. Probable formation of the tested compositions in the natural environment is discussed, as well as their possible application against the bacterial infections, which use the QS system for induction of their pathogenic potential.