Elf18 is a peptide derived from the N-terminal of elongation factor thermo unstable (EF-Tu), a highly conserved protein in bacteria which is essential for the synthesis of new proteins, and also a pathogen-associated molecular pattern (PAMP) protein - elicitors of plant defences, recognised by pattern recognition receptors. Arabidopsis plants specifically recognise the N terminus of EF-Tu, and elf18 is fully active as a mimetic and inducer of defence responses. In leaves of Arabidopsis plants, elf18 induces an oxidative burst and biosynthesis of ethylene, and triggers resistance to subsequent infection with pathogenic bacteria.