Complement resistance is essential for colonization of the digestive tract of Hirudo medicinalis by Aeromonas strains

The symbiotic association between Hirudo medicinalis and Aeromonas veronii bv. sorbia and colonization by the latter require the presence of serum complement system. A. veronii mutants lacking the complement system cannot colonize H. medicinalis but aquires the ability to colonize if the complement system is restored.