Phylogeny And Antibiotic Activity Of Xenorhabdus Spp. Isolated From Nematode Symbionts In Kenya

Xenorhabdus is a bacteria genus of the family Enterobacteriaceae. Bacteria of this genus form a mutualistic relationship with Steinernema entomopathogenic nematodes. More so, their antimicrobial production serves as a potential source of novel antibiotics in the wake of growing antimicrobial resistance. This study aimed to establish the phylogenetic relationship of three Xenorhabdus isolates to the 24 described species of the genus based on the 16s rRNA gene. Secondly, it aimed to determine the antibiotic activity of the three Xenorhabdus isolates from Kenya. Six 16s rRNA sequences were isolated in this study while 184 sequences were obtained from public databases compiling a data-set of 190 sequences. Phylogenetic reconstruction was done using maximum likelihood method with a bootstrap test of phylogeny of 500 replicates. The phylogenetic reconstruction identified the isolates as Xenorhabdus griffiniae L67, Xenorhabdus griffiniae XN45 and a novel Xenorhabdus species. This is the first record of Xenorhabdus griffiniae in Kenya. The antibiotic activities of the isolates were assessed by analysis of the inhibitory effect of the whole broth extracts, organic fractions and aqueous fractions. Xenorhabdus griffiniae L67, Xenorhabdus griffiniae XN45 and Xenorhabdus sp. P48 produced antibiotics effective against gram-positive bacteria. Xenorhabdus griffiniae L67 produced water-soluble antibiotics active against gram-positive bacteria. Xenorhabdus griffiniae XN45 produced antibiotics that readily dissolved in dimethyl sulfoxide. These were inhibitory to Methicillin resistant Staphylococcus aureus. The organic solvent fraction of Xenorhabdus griffiniae L67 had a peak uv absorption at 218nm.This indicated the presence of peptide antimicrobials from Xenorhabdus griffiniae that were active against Methicillin resistant Staphylococcus aureus.