The phytopathogenic bacteria Erwinia carotovora infects Drosophila and activates an immune response

Although Drosophila possesses potent immune responses, little is known abou t the microbial pathogens that infect Drosophila, We have identified member s of the bacterial genus Erwinia that induce the systemic expression of gen es encoding antimicrobial peptides in Drosophila larvae after ingestion, Th ese Erwinia strains are phytopathogens and use flies as vectors; our data s uggest that these strains have also evolved mechanisms for exploiting their insect vectors as hosts. Erwinia infections induce an antimicrobial respon se in Drosophila larvae with a preferential expression of antibacterial ver sus antifungal peptide-encoding genes. Antibacterial peptide gene expressio n after Erwinia infection is reduced in two Drosophila mutants that have re duced numbers of hemocytes, suggesting that blood cells play a role in regu lating Drosophila antimicrobial responses and also illustrating that this D rosophila-Erwinia interaction provides a powerful model for dissecting host -pathogen relationships.