Table 1.

Overview of microbial effectors

Microbial effector	Definition	Structure	Producer	Target	Resistance
Virulence factor	Molecules or structures that enable pathogens to infect hosts, evade immune defenses, or cause disease	Enzymes, toxins, adhesins	Bacteria, Archaea, Fungi, Viruses	Hosts including animals and plants	Usually slow, but fast adaptation by immune system
Toxins	Substances produced by organisms to damage host cells, disrupt biological functions, or cause toxicity	Complex metabolites (may contain amino acids)	Bacteria, Archaea, Fungi, Viruses	Hosts including animals and plants	Usually slow, but fast adaptation by immune system
Antimicrobial peptide	Short peptides produced to defend against bacteria, viruses fungi and tumor cells	Canonical amino acids	All species	broad range against bacteria, virus, fungi or parasites	Rare
Non-ribosomal peptide	Peptides synthesized by non-ribosomal peptide synthetase (NRPS) enzymes, not ribosomes	Peptide secondary metabolites	Bacteria, Archaea, Fungi	broad range against bacteria, virus, fungi or parasites	Rare
Antibiotics	Chemical compounds that specifically inhibit bacterial growth or kill bacteria	Diverse small molecules (may contain amino acids)	Bacteria, Archaea, Fungi	Target microbial structures	Frequent
Viruses	Infectious agents consisting of nucleic acids	Nucleic acids (DNA/RNA) and proteins; sometimes lipids	Self-reproducing in hosts	All domains	Usually slow, but fast adaptation by immune system