Galleria mellonella as a complementary model organism to study the enteropathogenic E. coli Type 3 Secretion System
Isabel Forlastro1, Rebecca McQuade2, V. K. Viswanathan1 and S. Patricia Stock1,2,3
1Department of Microbiology, School of Animal and Comparative Biomedical Sciences, 2Center for Insect Science, 3Department of Entomology, The University of Arizona
Enteropathogenic Escherichia coli (EPEC) is a common diarrheal pathogen that affects approximately 0.8 million children per year in developing countries. EPEC uses a complex bacterial structure called the Type III Secretion System (T3SS) to inject bacterial effector proteins directly into intestinal epithelial cells, manipulating the cells’ behavior and causing disease. Rabbits are a commonly used model to study EPEC. However, rabbits have several limitations as hosts including expense, specialized handling, ethical concerns and federal regulations regarding the use of laboratory vertebrates. Insects are potential complementary models for studying bacterial pathogenesis in vivo. Benefits of using insect hosts include low-cost, ability for mass infections, and analogous immune strategies to vertebrates. We hypothesize that larvae of the greater wax moth Galleria mellonella (GM) can serve as an effective model in studying the EPEC T3SS. In order to determine if EPEC can infect GM we injected EPEC into the body cavity (hemocoel) of the insects. We observed that live wild-type EPEC kills GM and that heat-killed EPEC does not kill, indicating that EPEC actively infects GM. To explore the mechanism of killing, we also considered EPEC mutant strains that lack different components of the T3SS. These mutants were defective in killing GM,indicating that EPEC kills these insects in a T3SS-dependent manner. To identify tissue localization of EPEC, we injected YFP-labeled EPEC into GM and observed fluorescence along the insect gut. We are currently adapting this model to test potential T3SS inhibitors and to study individual T3SS effectors. We are also attempting to model oral infections in insects to more closely represent human infection.