The Carnobacterium genus contains nine ubiquitous species of lactic acid bacteria isolated from cold to temperate environments (Leisner et al., 2007). The species Carnobacterium inhibens is a motile gram-positive bacterium first isolated from the intestine of the Atlantic Salmon (Salmo salar). C. inhibens inhibits bacterial growth of pathogenic Vibrio anguillarum and Aeromonas salmonicida by producing bacteriocins and antimicrobial peptides. Our group isolated a C. inhibens strain from a sample of fresh water of the Mapocho River in the city of Santiago de Chile with capacity to inhibit various clinically relevant bacterial pathogens in vitro. Nonetheless, safety of this strain has not been assessed. In this work we studied the effect of feeding the Chilean isolate C. inhibens to C. elegans. We evaluated the worm behavior and development while feeding on C. inhibens. Within the first hours animals develop major body paralysis with largely reduced pharynx pumping. 100% of L4 worms died 24 hours after exposure to C. inhibens. Strikingly, avoidance behavior in this C. inhibens strain develops much faster than in any other pathogenic bacteria reported, showing 25% of avoidance during the first 10 minutes and complete avoidance after 24 hours. The molecule that affects C. elegans is not volatile, because when constructing a plate with C. inhibens containing a smaller plate in its interior with worms fed with Escherichia coli OP50 and sharing the same environment that the toxic bacteria, these worms did not suffer any damage. This suggested that the toxic molecule needs to be ingested. To test this hypothesis, we exposed 1% SDS resistant daf-2 dauers at 25 deg C to C. inhibens. All dauers survived, indicating that the bacteria need to be eaten to cause its effect. All animals died after recovering from dauer. This suggests that this C. inhibits strain may not be innocuous for animal hosts and offers a platform for studying the molecules involved in the early response of the worm to pathogenic bacteria and prompts the identification of the bacterial molecules involved in the killing and their mechanism.

Affiliations:
- Instituto de Ciencias Biomedicas, Facultad de Medicina, Universidad de Chile.
- Centro de Genomica y Bioinformatica, Facultad de Ciencias, Universidad Mayor, Chile.
- Centro Interdiciplinario de Neurociencia de Valparaiso (CINV).