title: An improved method for generating axenic entomopathogenic nematodes.
abstract: BACKGROUND
  Steinernema carpocapsae are parasitic nematodes that invade and kill insects. The nematodes are mutualistically associated with the bacteria Xenorhabdus nematophila and together form an excellent model to study pathogen infection processes and host anti-nematode/antibacterial immune responses. To determine the contribution of S. carpocapsae and their associated X. nematophila to the successful infection of insects as well as to investigate the interaction of each mutualistic partner with the insect immune system, it is important to develop and establish robust methods for generating nematodes devoid of their bacteria.
  
  
  RESULTS
  To produce S. carpocapsae nematodes without their associated X. nematophila bacteria, we have modified a previous method, which involves the use of a X. nematophila rpoS mutant strain that fails to colonize the intestine of the worms. We confirmed the absence of bacteria in the nematodes using a molecular diagnostic and two rounds of an axenicity assay involving appropriate antibiotics and nematode surface sterilization. We used axenic and symbiotic S. carpocapsae to infect Drosophila melanogaster larvae and found that both types of nematodes were able to cause insect death at similar rates.
  
  
  CONCLUSIONS
  Generation of entomopathogenic nematodes lacking their mutualistic bacteria provides an excellent tool to dissect the molecular and genetic basis of nematode parasitism and to identify the insect host immune factors that participate in the immune response against nematode infections.
authors.affiliation: Insect Infection and Immunity Lab, Department of Biological Sciences, Institute for Biomedical Sciences, The George Washington University, Washington DC, USA. shrutiyadav@gwmail.gwu.edu.
authors.forename: Shruti
authors.initials: S
authors.lastname: Yadav
authors.affiliation: Insect Infection and Immunity Lab, Department of Biological Sciences, Institute for Biomedical Sciences, The George Washington University, Washington DC, USA. upasana@gwmail.gwu.edu.
authors.forename: Upasana
authors.initials: U
authors.lastname: Shokal
authors.affiliation: Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, WI, USA. sforst@uwm.edu.
authors.forename: Steven
authors.initials: S
authors.lastname: Forst
authors.affiliation: Insect Infection and Immunity Lab, Department of Biological Sciences, Institute for Biomedical Sciences, The George Washington University, Washington DC, USA. ioannise@gwu.edu.
authors.forename: Ioannis
authors.initials: I
authors.lastname: Eleftherianos
mesh_terms: D000818:Animals; D035843:Biomedical Research / Q000379:methods*; D004331:Drosophila melanogaster; D006790:Host-Parasite Interactions; D009348:Nematoda; D013559:Symbiosis; D020593:Xenorhabdus