<i>Drosophila melanogaster</i> bacterial pre-exposure.

(A) Experimental scheme. Oregon-R wild-type flies (P, Parental generation) were reared and allowed to oviposit on normal untreated diet. After parent removal, the progeny (F1 generation) completed their development on diet supplemented with Luria-Bertani media (LB), a mix of live Escherichia coli and Micrococcus luteus (Ec+Ml), or a mix of heat-killed bacteria (HK Ec+Ml) (Pre-exposure). (B) Effect of pre-exposure to live (Ec+Ml) or dead (HK Ec+Ml) bacteria on the transcript levels of the antimicrobial peptide genes Diptericin-A (B) and Drosomycin (C) in larvae, pupae and young adult flies (1–3 day-old) of D. melanogaster. All values were normalized to LB-containing media controls and analyzed using unpaired t-test. Error bars represent standard error of the mean. (D) Longevity of D. melanogaster following pre-exposure to live (Ec+Ml) or dead (HK Ec+Ml) bacteria. Fly mortality for each treatment is shown over a 70-day period. A log-rank (Mantel Cox) test performed using GraphPad Prism software did not detect significant differences between the survival curves (P = 0.3873), indicating that any effect on longevity produced by pre-exposure is relatively slight and inconsequential.