A Septic Pinprick Technique to Introduce Systemic Bacterial Infection in Flies

To investigate the immune response of Drosophila against pathogenic microbes, take a suspension of viable bacterial pathogens. Dip a sterile needle into the suspension, collecting a small amount.

Place an anesthetized fly under a dissection microscope. With the infected needle, prick the fly at the sternopleural plate of the thorax. The prick introduces bacteria into the hemolymph — circulatory fluid in the body cavity.

Place the infected flies inside a vial containing fly food, and maintain them for an adequate period.

The bacteria utilize the hemolymph as a rich source of nutrients and multiply — resulting in a systemic infection. Hemolymph contains hemocytes, circulating immune effector cells.

The hemolymph is also associated with the fat body, a specialized tissue for energy storage. The pattern recognition receptors on the fat body cells interact with the bacteria. This interaction induces the cells to secrete antimicrobial peptides, mediating bacterial killing.

The circulating hemocytes interact with the bacteria via phagocytic receptors, causing their engulfment into phagosomes and resulting in bacterial degradation.

A subset of the pathogens evades the host's immune response, leading to the death of the flies.

Monitor the fly mortality and perform downstream assays to assess the immune response against the pathogen.