The Nematode Caenorhabditis elegans as an Alternative Model for Bacterial Infection

Abstract

The usefulness of the nematode Caenorhabditis elegans as a model of bacterial infection has been assessed. Initially a plate-based mortality assay was established using Pseudomonas aeruginosa. A novel method for assessing bacterial virulence towards C. elegans in liquid media was also developed. These assays were used to investigate the virulence of strains from the Burkholderia cepacia complex, Burkholderia pseudomallei and Burkholderia thailandensis. The results from the plate-based mortality assay mirrored the virulence of B. pseudomallei and B. thailandensis in mammals. However the results also showed that this method was not suitable for the investigation of the B. cepacia complex. Assays carried out in liquid media were not a robust measure of bacterial virulence for any of the Burkholderia strains tested. The C. elegans model was also used to investigate virulence mechanisms of B. pseudomallei. B. pseudomallei can adhere to and invade a variety of mammalian cell types. Transmission electron microscopy was used to investigate the interactions of B. pseudomallei with the cells of the C. elegans gut. No evidence of adherent bacterial cells or invasion of the tissues surrounding the gut was seen. A panel of B. pseudomallei transposon mutants was screened in C. elegans. A single transposon mutant was identified that was attenuated in nematodes and was subsequently also shown to be attenuated in BALB/c mice. The interrupted gene encoded a putative aldehyde dehydrogenase. This protein has not been previously shown to play a role in the virulence of B. pseudomallei. The nematode model was also used to screen a B. pseudomallei genomic cosmid library in E. coli for clones with increased virulence. However the data indicated that this method could not be utilised for the identification of B. pseudomallei virulence genes without further development.