Biosynthesis of silver nanoparticles (AgNPs) by marine bacteria especially luminescent Vibrio species is least investigated. In this study, AgNPs were first synthesized by the culture supernatant of a luminescent bacterium (Vibrio sp. B4L) and then, the prepared samples were characterized employing several techniques. The antibacterial activity of the AgNPs was investigated against Escherichia coli and Staphylococcus aureus using disk diffusion agar and broth microdilution methods. The growth curve, Reactive Oxygen Species (ROS) formation, and Lactate Dehydrogenase (LDH) activity of the samples were measured along with Field Emission Scanning Electron Microscopy (FESEM) observation and inhibition of biofilm formation. Dynamic light scattering (DLS) analysis showed that the average particle size of the synthesized AgNPs was in the range of about 32.67-107.18 nm and the polydispersity index (PDI) of 0.1120 indicated the formation of monodispersed particles. The average zeta potential of AgNPs obtained -36.15 mV, showing the high stability of biosynthetic nanoparticles. Antibacterial studies indicated that not only the AgNPs had antibacterial activity but also increased the antibacterial properties of tetracycline when used in combination. ROS production was enhanced in a dose-dependent manner. A high difference in LDH activities was found between AgNPs treated cells and the control group. FESEM images revealed membrane disruption and lysis in AgNPs treated cells. The formation of E.coli biofilm was 100% inhibited at 62.5 µg/ml showing that our bacteriogenic AgNPs can be a potential alternative remedies for controlling antibiotic-resistant pathogens.

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