Nowadays, infectious microorganisms show a significant tolerance and become more and more resistant to currently used antibiotics. The present study aims to evaluate the effect of Thymoquinone (TQ) (The main gradient of Nigella sativa seeds) either free or encapsulated in (1,2-dipalmitoyl-Sn-glycero-3- phosphocholine) DPPC liposomes on the antimicrobial activity of several microorganisms (Escherichia coli, Staphylococcus aureus, Candida albicans, Aspergillus brasiliensis). DPPC liposomes and TQ-encapsulated DPPC liposomes were characterized by the measurement of the liposomal size, zeta potential, differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy, UVvisible spectrum, transmission electron microscope in addition to the measurement of the refractive index. The encapsulation efficiency of the TQ-encapsulated liposome was found to be more than 90%. The liposomal size of TQ-encapsulated DPPC liposomes showed an increase relative to DPPC liposomes. Moreover, the results obtained for the zeta potential (-17.7 mV for DPPC liposomes versus -7.06 mv for TQ-encapsulated DPPC liposomes) indicated that the DPPC had become less stable due to the TQ-DPPC encapsulation, meaning a loss of repulsive forces between particles and a higher tendency of aggregation. DSC results demonstrated a higher phase transition of TQ-encapsulated DPPC liposomes when compared to free DPPC lisposomes indicating that the hydrocarbon chains of lipid molecules arranged more closer due to TQ encapsulation. We also examined the antimicrobial activity of both free DPPC and TQ-encapsulated DPPC liposomes by the zone Inhibition method against several types of microorganisms. The antimicrobial action of both Escherichia coli, Staphylococcus aureus species were not changed by any of the tested formulation. Free thymoquinone showed a moderate antimicrobial activity on Candida albicans, however, neither DPPC nor TQ-encapsulated DPPC liposomes showed any effect on the same yeast species. Regarding the Aspergillus brasiliensis, it demonstrated a mild antimicrobial effect by both the DPPC and TQ-encapsulated DPPC Liposomes. In conclusion, encapsulation of DPPC liposomes with TQ greatly alter the physical and chemical properties of DPPC liposomes. TQ-encapsulated DPPC liposomes can be utilized as an antimicrobial agent against the Aspergillusbrasiliensis fungi.
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