Effect of Capsicum Frutescens Extract, Capsaicin, and Luteolin on Quorum Sensing Regulated Phenotypes

Abstract

Capsicum peppers have not been investigated as sources of quorum sensing (QS) inhibitors. This study aimed to identify compounds in pimenta‐malagueta (Capsicum frutescens) and red pepper (Capsicum annuum) extracts and to evaluate their effect on violacein production in Chromobacterium violaceum ATCC 12472 and C. violaceum CV026, as well as biofilm formation (BF) in Pseudomonas aeruginosa PAO1 and Serratia marcescens MG1. Among the extracts, pimenta‐malagueta methanolic extract (PMME) was chosen because it contained capsaicin, dihydrocapsaicin, and luteolin in greater amount than the other extracts. In general, PMME partially inhibited bacterial growth at 2.5 and 5.0 mg/mL, as well as capsaicin at 100 µg/mL and luteolin at 62.5, 125, and 250 µg/mL. At lower concentrations, PMME and luteolin reduced violacein production in C. violaceum ATCC 12472 without affecting growth, a result that was not observed with capsaicin. We show that violacein inhibition by PMME is likely due to luteolin. In silico docking evaluation showed that luteolin binds to the CviR QS regulator. Crystal violet staining and confocal microscopy revealed that BF was increased by PMME and capsaicin, being remarkably superior for P. aeruginosa PAO1 at 30 °C. Capsaicin is not an effective QS inhibitor, while luteolin should be further investigated for its potential effects in QS regulated phenotypes. Practical Application Quorum sensing (QS) is a form of bacterial communication targeted for studies aiming to inhibit bacterial virulence. QS regulates phenotypes that influence microbial activities across many areas, including Food Science. Capsicum frutescens is a type of chili pepper consumed in Brazil, rich in bioactive compounds such as capsaicin (which gives its pungency) and luteolin (a phenolic compound). We show that C. frutescens extract and luteolin inhibit QS in a model bacterium, along with the possible molecular mechanism of inhibition. Capsaicin did not inhibit QS neither biofilm formation. Luteolin should be further investigated for its QS inhibition properties and biotechnological applications.

Single components of botanicals and nature-identical compounds as a non-antibiotic strategy to ameliorate health status and improve performance in poultry and pigs

“…Capsaicin (trans-8-methyl-N-vanillyl-6-nonenamide) is a monoterpene alkaloid, considered the major pungent component in the genus Capsicum. It is characterised by antioxidant, hypotensive and antimicrobial effects (149)(150)(151) . The antimicrobial targets of capsaicin have not been identified yet (149) but it can reduce cell-invasiveness of Streptococcus (cell-invasive group A) in vitro (152) .…”

Phenotypic and genotypic analysis of biofilm production by Pseudomonas aeruginosa isolates from infection and colonization samples

“…Biofilm formation is a complex virulence mechanism, which requires gene regulation by different components of the QS system. Changes in the expression of the genes related to the QS network or the presence of mutations can reduce the production of this important bacterial virulence factor 1,12,17 . The detection of the presence of the QS genes associated with the phenotypic analysis of biofilm production can help in the evaluation of their regulation.…”

“…Additionally, reports from studies in the literature indicate that similar results were obtained using isolates from patients with chronic infections as these individuals are in an environment favorable for the appearance of random mutations. Further, antibiotic therapy promotes the artificial selection of bacteria for greater drug resistance, primarily in cases where P. aeruginosa infection is present, as the mucopolysaccharide constituting the biofilm hinders drug diffusion through cell layers 1,14,17,26 .…”

“…At high concentrations, these molecules stimulate biofilm production due to the transcription of specific genes. This complex communication mechanism is called quorum sensing (QS) 13,16,17 . QS enables P. aeruginosa to respond to the self-inducting molecules called acyl-homoserine lactones (AHLs) that target the Las and Rhl genes.…”

“…Further, the lasI, rhlI, and pqsA genes are responsible for the biosynthesis of the signaling molecules N-(3-oxododecanoyl)-L-homoserine lactone (OdDHL), N-Butyrylhomoserine lactone (BHL), and the Pseudomonas quinolone signal (PQS), respectively. The corresponding receptors for the signaling molecules are LasR, RhlR, and PqsR, respectively, which are involved in the regulation of bacterial virulence and biofilm formation 17,18,19,20 .…”