Isolation, Identification and Antimicrobial Activities of Four Bacteria Associated with Entomopathogenic Nematodes, Steinernema spp.

Abstract

Recently, the search for novel products derived from natural sources has become necessary due to the decreasing effectiveness of current antibiotics in treating bacteria that are antibiotic-resistant. In this context, it is well known that entomopathogenic bacteria (EPBs) produce a broad range of secondary metabolites with antibacterial activities. Therefore, an in-vitro trial was conducted to isolate and identify non-symbiotic bacteria associated with entomopathogenic nematodes, Steinernema spp. and evaluate the antibacterial activity against four antibiotic-resistant bacteria. Four bacterial isolates, i.e. Pseudomonas alcaligenes ST-1, Paenibacillus barcinonensis ST-2, Bacillus mojavensis ST-3, and Bacillus megaterium ST-4 were non-symbiotically isolated from the heamolymph of dead Steinernema-infected Galleria mellonella larvae and molecularly characterized. The bacterial cells and filtrates from P. alcaligenes ST-1 strongly inhibited the growth of Staphylococcus aureus through disk diffusion (43 mm), minimum inhibitory concentration (2.5 µL/mL), and minimal bactericidal concentration (5 µL/mL) assay. Conclusively, the direct application of endogenous Steinernema-associated EPB as an antibacterial agent for antibiotic-resistant bacteria looked promising.