Abstract
Xenorhabdus and Photorhabdus, symbiotically associated with entomopathogenic nematodes (EPNs), produce a range of antimicrobial compounds. The objective of this study is to identify Xenorhabdus and Photorhabdus and 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 six Xenorhabdus isolates and eight Photorhabdus isolates, were obtained from 230 soil samples. Based on the BLASTN search incorporating the phylogenetic analysis of a partial recA gene, all six isolates of Xenorhabdus were found to be identical and closely related to X. stockiae. Five isolates of Photorhabdus were found to be identical and closely related to P. luminescens subsp. akhurstii. Two isolates of Photorhabdus were found to be identical and closely related to P. luminescens subsp. hainanensis. The remaining isolate of Photorhabdus was found to be identical to P. asymbiotica subsp. australis. The bacterial extracts from P. luminescens subsp. akhurstii showed strong inhibition the growth of S. aureus strain PB36 (MSRA) by disk diffusion, minimal inhibitory concentration, and minimal bactericidal concentration assay. The combination between each extract from Xenorhabdus/Photorhabdus and oxacillin or vancomycin against S. aureus strain PB36 (MRSA) exhibited no interaction on checkerboard assay. Moreover, killing curve assay of P. luminescens subsp. akhurstii extracts against S. aureus strain PB36 exhibited a steady reduction of 105 CFU/ml to 103 CFU/ml within 30 min. This study demonstrates that Xenorhabdus and Photorhabdus, showed antibacterial activity. This finding may be useful for further research on antibiotic production.
Highlights
Antibiotic-resistant bacteria have become an emerging public health problem
A total of 46 sample sites with 230 soil samples yielded 14 isolates of entomopathogenic nematodes (EPNs) belonging to the genus Steinernema and Heterorhabditis
After the BLASTN search, six isolates of Steinernema were identified as S. surkhetense (99% identity) while two isolates of Heterorhabditis were identified as H. indica (99% identity)
Summary
Pseudomonas aeruginosa, Klebsiella pneumoniae, Escherichia coli, Staphylococcus aureus, Acinetobacter baumannii, and Enterococcus faecalis are the major sources of antibiotic-resistant bacteria [1] These bacteria develop new resistance mechanisms with the emergence and the spread of the disease. Xenorhabdus and Photorhabdus, the symbiotic bacteria associated with entomopathogenic nematodes (EPNs), have been reported to be bacterial resources for the production of antimicrobial compounds Their cell suspension and metabolite compound activities effectively inhibit the growth of Staphylococcus pyogenes and S. aureus [7,8], Bacillus subtilis, Botrytis cinerea [9], Escherichia coli, Klebsiella pneumoniae, Enterobacter coloacae [10], Fusicladium effusum [11], Bacillus anthracis, Phytophthora capsici, and Rhizoctonia solani [12]
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