Citrus Extracts as Inhibitors of Quorum Sensing, Biofilm Formation and Motility of Campylobacter jejuni

Quorum Sensing (QS), a signaling system present in bacteria, influences the expression of a variety of virulence factors. This study investigated the ability of citrus extracts to inhibit the activity of AI-2 molecules that mediate QS in Campylobacter jejuni and the effects of these extracts on motility, biofilm formation and expression of flaA-B. Cultures of C. jejuni were exposed to extracts of Citrus limon, Citrus medica and Citrus aurantium peels at various concentrations. Swarm motility tests were performed in Muller Hinton agar; biofilm formation was determined colorimetrically in microtiter plates; AI-2 activity was measured with a bioluminescence assay using V. harveyi; and flaA-B expression was determined by qRT-PCR. Treatment with C. limon or C. medica peel extract reduced swarm motility 44-59%, whereas treatment with C. aurantium extract reduced swarm motility 35-40%. Biofilm formation was reduced 60-75 % by these extracts, depending on extract concentration and /or strain tested. All three citrus extracts decreased AI-2 activity by about 90 %, and at 75 % of MBC, significantly (P <= 0.05) reduced expression of flaA-B. These findings provide preliminary metabolic and molecular insights into the effects of edible antimicrobials on QS and virulence factors of C. jejuni.