Aims:  The goal of this work was to investigate the influence of DMSO, garlic extract and p‐coumaric acid on bacterial quorum sensing (QS). Methods and Results:  The decreases in the QS responses of QS reporter strains Escherichia coli pSB401 and pSB536, Agrobacterium tumefaciens NTL4, Chromobacterium violaceum 5999 and wt 494, Pseudomonas putida IsoF/gfp and environmental Pseudomonas chlororaphis were quantified in relation to growth inhibitory effects. DMSO showed no significant QS‐specific effects on the strains tested even at close‐to‐lethal concentrations. Garlic extracts antagonized the activity of QS receptors LuxR, AhyR and TraR, but were toxic at higher concentrations. P‐coumaric acid fully inhibited QS responses of 5999, NTL4 and P. chlororaphis, with no influence on cell viability. Conclusions:  The quorum sensing inhibition activity of garlic was extended to novel receptors, and p‐coumaric acid was found to possess previously undescribed QS antagonist properties. Significance and Impact of the Study:  The results suggest that p‐coumaric acid might act as QS inhibitor. Further studies are required to understand its role in the regulation of QS and investigate structurally related compounds.