Temperature-Dependent Galleria mellonella Mortality as a Result of Yersinia entomophaga Infection
ABSTRACTThe bacteriumYersinia entomophagais pathogenic to a range of insect species, with death typically occurring within 2 to 5 days of ingestion.Per oschallenge of larvae of the greater wax moth (Galleria mellonella) confirmed thatY. entomophagawas virulent when fed to larvae held at 25°C but was avirulent when fed to larvae maintained at 37°C. At 25°C, a dose of ∼4 × 107CFU per larva of aY. entomophagatoxin complex (Yen-TC) deletion derivative, theY. entomophagaΔTC variant, resulted in 27% mortality. This low level of activity was restored to near-wild-type levels by augmentation of the diet with a sublethal dose of purified Yen-TC. Intrahemocoelic injection of ∼3Y. entomophagaorY. entomophagaΔTC cells per larva gave a 4-day median lethal dose, with similar levels of mortality observed at both 25 and 37°C. Following intrahemocoelic injection of a Yen-TC YenA1 green fluorescent protein fusion strain into larvae maintained at 25°C, the bacteria did not fluoresce until the population density reached 2 × 107CFU ml−1of hemolymph. The observed cells also took an irregular form. When the larvae were maintained at 37°C, the cells were small and the observed fluorescence was sporadic and weak, being more consistent at a population density of ∼3 × 109CFU ml−1of hemolymph. These findings provide further understanding of the pathobiology ofY. entomophagain insects, showing that the bacterium gains direct access to the hemocoelic cavity, from where it rapidly multiplies to cause disease.