Exploring Common Culinary Herbs and Spices as Potential Anti-Quorum Sensing Agents

Quorum sensing controls bacterial pathogenesis and virulence; hence, interrupting this system renders pathogenic bacteria non-virulent, and presents a novel treatment for various bacterial infections. In the search for novel anti-quorum sensing (AQS) compounds, 14 common culinary herbs and spices were screened for potential antipathogenicity activity against Chromobacterium violaceum ATCC 12472. Extracts of Glycyrrhiza glabra (liquorice), Apium graveolens (celery), Capsicum annuum (cayenne pepper) and Syzygium anisatum (aniseed) demonstrated good AQS potential, yielding opaque halo zones ranging from 12–19 mm diameter at sub-minimum inhibitory concentrations (0.350–4.00 mg/mL). For the same species, the percentage reduction in violacein production ranged from 56.4 to 97.3%. Zones with violacein inhibitory effects were evident in a celery extract analysed using high performance thin layer chromatography-bio-autography. The major active compound was isolated from celery using preparative-high performance liquid chromatography-mass spectrometry and identified using gas chromatography-mass spectrometry (GC-MS) as 3-n-butyl-4,5-dihydrophthalide (sedanenolide). Potent opaque zones of inhibition observed on the HPTLC-bio-autography plate seeded with C. violaceum confirmed that sedanenolide was probably largely responsible for the AQS activity of celery. The bacteriocidal properties of many herbs and spices are reported. This study, however, was focussed on AQS activity, and may serve as initial scientific validation for the anti-infective properties ascribed to several culinary herbs and spices.