Fig 2. Experimental set up for Drosophila melanogaster bacterial pre-exposure, subsequent infection, and incubation.

Oregon-R wild-type flies (P, Parental generation) were raised and allowed to lay eggs on normal untreated food. Parent flies were then removed from the vials and the progeny (F1 generation) were fed on food containing a mix of live Escherichia coli and Micrococcus luteus (Ec+Ml), a mix of heat-killed bacteria (HK Ec+Ml) or on control media supplemented with Luria-Bertani (LB) (Pre-exposure). Pre-exposed flies were then injected intrathoracically with phosphate-buffered saline (PBS), a non-pathogenic strain of E. coli, or the insect pathogenic bacteria Photorhabdus luminescens and P. asymbiotica. After injection, adult flies were incubated in vials containing normal untreated media.