Antibacterial activity of Xenorhabdus and Photorhabdus isolated from entomopathogenic nematodes against antibiotic-resistant bacteria

XenorhabdusandPhotorhabdus, symbiotically associated with entomopathogenic nematodes (EPNs), produce a range of antimicrobial compounds. The objective of this study is to identifyXenorhabdusandPhotorhabdusand their EPNs hosts, which were isolated from soil samples from Saraburi province, and study their antibacterial activity against 15 strains of drug-resistant bacteria. Fourteen isolates (6.1%), consisting of sixXenorhabdusisolates and eightPhotorhabdusisolates, were obtained from 230 soil samples. Based on the BLASTN search incorporating the phylogenetic analysis of a partialrecAgene, all six isolates ofXenorhabduswere found to be identical and closely related toX.stockiae. Five isolates ofPhotorhabduswere found to be identical and closely related toP.luminescenssubsp.akhurstii. Two isolates ofPhotorhabduswere found to be identical and closely related toP.luminescenssubsp.hainanensis. The remaining isolate ofPhotorhabduswas found to be identical toP.asymbioticasubsp.australis. The bacterial extracts fromP.luminescenssubsp.akhurstiishowed strong inhibition the growth ofS.aureusstrain PB36 (MSRA) by disk diffusion, minimal inhibitory concentration, and minimal bactericidal concentration assay. The combination between each extract fromXenorhabdus/Photorhabdusand oxacillin or vancomycin againstS.aureusstrain PB36 (MRSA) exhibited no interaction on checkerboard assay. Moreover, killing curve assay ofP.luminescenssubsp.akhurstiiextracts againstS.aureusstrain PB36 exhibited a steady reduction of 10(5)CFU/ml to 10(3)CFU/ml within 30 min. This study demonstrates thatXenorhabdusandPhotorhabdus, showed antibacterial activity. This finding may be useful for further research on antibiotic production.