C. elegans: model host and tool for antimicrobial drug discovery

Abstract

For almost four decades, the nematode Caenorhabditis elegans has been of great value in many fields of biological research. It is now used extensively in studies of microbial pathogenesis and innate immunity. The worm lacks an adaptive immune system and relies solely on its innate immune defences to cope with pathogen attack. Infectious microbes, many of which are of clinical interest, trigger specific mechanisms of innate immunity, and provoke the expression of antifungal or antibacterial polypeptides. In this review, we highlight some of these families of antimicrobial peptides (AMPs) and proteins that are candidates for the development of novel antibiotics. In addition, we describe how systems of C. elegans infection provide an increasing number of possibilities for large-scale in vivo screens for the discovery of new antimicrobial drugs. These systems open promising perspectives for innovative human therapies.

Fig. 1.

C. elegans antimicrobial defences. (A) Basic anatomy of C. elegans. The worm is composed essentially of two concentric tubes – the epidermis (also called hypodermis) and the intestine – separated by a fluid cavity, the pseudocoelom. The physical barriers of the worm include a grinder, which mechanically disrupts the bacteria that form the worm’s normal diet, and the cuticle, which envelops the animal. (B) Selected AMPs and proteins in C. elegans. Invading microbes induce cell damage and are also believed to be detected via specific pathogen receptors. These two events trigger specific signalling pathways that lead to the production and release of a variety of specific antimicrobial proteins and AMPs (yellow boxes). Depending on the pathogen, these antimicrobial effectors are expressed specifically in a particular tissue, such as the pharynx, the intestine or the epidermis. Figure adapted with permission (Millet and Ewbank, 2004).

Fig. 2.

A simplified protocol to screen in vivo for new antimicrobial compounds using an established C. elegans infection system and an automated high-throughput assay. After culture and amplification of nematodes on growth plates (seeded with a non-pathogenic E. coli strain), synchronized populations of worms are transferred to infection plates that have been seeded with pathogenic E. faecalis. After half a day, worms are washed off the plates and 15–25 individuals are added to each well of 96-well (shown here) or 384-well microtiter plates that have been pre-loaded with different compounds. After 5 days, the worms in each well are assayed for their survival, using the vital dye SYTOX. Because it is only taken up by dead worms, measuring worm survival can be automated using image analysis software. Wells in which worms live substantially longer contain candidate antibiotics. The figure summarizes the approach taken by Moy et al. (Moy et al., 2009).