Caenorhabditis elegans as a simple model host for studying foodborne pathogens

Food matrices represent a potential reservoir of infectious bacteria and foodborne pathogens constitute a risk to consumer health. Despite this realization and efforts in monitoring undesirable microorganisms in food matrices, there is limited information available on the presence and function of virulence factors in foodborne bacteria nor their mechanisms of pathogenesis are fully understood. In order to investigate infectious microbes the nematode Caenorhabditis elegans can be used as a simple and well-established model host. Comprehensive studies have reported the worm as a versatile model metazoan in which to assess the virulence of many human pathogens. Despite the progress made using this model only few studies employed the nematode to investigate foodborne pathogenesis. In this study we used the C. elegans model to analyse the role of two potential foodborne emerging pathogens: Enterococcus italicus and Lactococcus garvieae. E. italicus, a novel Enterococcus species isolated from dairy products, needs to be better studied for defining its biotechnology potential and pathogenic activity. L. garvieae causes septicaemia in fish leading to serious damage to fish aquaculture worldwide and has also been isolated from dairy and meat products. In this study we successfully applied nematode killing assay to assess the pathogenic activity of the two lactic acid bacteria. Strains were grown in both aerobic and anaerobic conditions and tested against C. elegans. When grown in anaerobic conditions, both strains showed a stronger nematode killing phenotype compared to aerobic ones. Genome-wide analysis of the E. italicus and L. garvieae genomes revealed the presence of genes encoding for NADH oxidase (nox) and superoxide dismutase (sod) supporting the hypothesis that under anaerobic conditions this strain may produce hydrogen peroxide, a known toxic compound for the worm. Using RT-PCR experiments we are testing the expression and regulation process of nox and sod in different cultural conditions. The aim of the study was to correlate the nematocidal activity of the two foodborne emerging pathogens E. italicus and L. garvieae to the involvement of hydrogen peroxide as putative virulence factor.