A facile microwave assisted synthesis of thymohydroquinone with antibiofilm properties against Salmonella typhi and Listeria monocytogenes

Abstract

Thymoquinone (TQ), a monoterpene isolated from the Nigella sativa L. seeds using the oil expeller method, gave about 40% of the total oil. Clevenger hydrodistillation of the obtained oil yielded volatile oil (0.55%) with 30% of TQ. Subsequent purification through silica gel column chromatography resulted in the isolation of pure TQ. The microwave assisted reduction of TQ with zinc and acetic acid resulted in the formation of thymohydroquinone within 5 min (THQ, yield 85%). The conventional reduction method gives 42% - 60% yield and is found to be time-consuming (4–12 h). The prepared THQ was tested at various concentrations for the inhibition of planktonic as well as biofilm of Listeria monocytogenes Scott A and Salmonella typhi FB231 bacterial cultures. Minimum inhibitory concentration (MIC) using MTT assay showed 50 μg/mL and 100 μg/mL for L. monocytogenes and S. typhi, respectively. Further, the biofilm growth inhibition and development were assessed using a crystal violet (CV) assay, which confirmed that THQ and TQ significantly eradicated biofilm formed after 6 h and 24 h, as evidenced by bright field microscopy. Thus, the results provide scope on the quicker microwave assisted synthesis, which is considered a greener method and the THQ showed potential antimicrobial and antibiofilm activities against common food borne pathogens.