Investigation of antimicrobial and anti-quorum sensing activities of some synthetic chemicals and natural extracts

Antibiotics play an important role for the human health. Therefore, discovery of new antibiotics and development of new therapeutic strategies to combat infectious diseases is of paramount importance. One of these approaches involves the inhibition of the quorum sensing system of bacteria, which is responsible for growth, adherence, biofilm and spore formation, and synthesis of virulence factors using various compounds. A number of natural and synthetic molecules that inhibited bacterial quorum sensing have been reported in the literature. In this study, derivatives of some synthetic Norfloxacin, Ciprofloxacin, Piperazine, Penicillanic acid, Cephallosporinic acid, Morpholine, Triazole, Nitro-Benzoyl Chlorid, Thiomorpholine, Imidazole, Pyridine, Nitro-pyridin, Cinnamaldehyde, and Dihydropyridine, and some natural substances such as green tea, vanilla, grape seed extract, and propolis are tested for their antimicrobial and anti-quorum sensing activities. Antimicrobial activity is determined using the agar-well diffusion method against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Enterococcus faecalis, Bacillus subtilis, Acinetobacter haemolyticus, Enterobacter aerogenes, Klebsiella pneumoniae, Listeria monocytogenes, Proteus mirabilis, Salmonella Typhimurium, Candida albicans ve Candida parapsilosis and anti-qorum sensing activity is investigated using agar-well diffusion and spectrophotometric methods against the Chromobacterium violaceum indicator strains. Among all the tested derivatives, three thiomorpholine, and two ciprofloxacin derivatives showed inhibitory activity against all bacteria tested with the concentrations ranging from 0.09-3.12 µg/ml, and 0.04-3.12 µg/ml, respectively. Two piperazine and eight norfloxacin derivatives showed inhibitory activity against most bacteria tested at concentrations ranging from 0.02-3.12 µg/ml and 0.09-6.25 µg/ml, respectively, and one cephalosporinic acid derivative showed inhibitory activity against only Proteus mirabilis at 3.12 µg/ml concentration. None of these derivatives exhibited anti-yeast activity. Three semi-synthetic cumin, two cephallosporinic acid, two thiomorpholine, and one penicillanic acid derivative showed anti-quorum sensing activity. Among the synthetic and natural molecules that have been used in this study, 16 and 8 were found to have antimicrobial and anti-QS activity, respectively. These results showed that the activity observed agents might have the potential to be used in the development of new antibacterial and anti-QS molecules.