Multiple strains representing four species of bacteria belonging to the genus Providencia have been isolated from wild caught Drosophila melanogaster: Providencia sneebia, Providencia burhodogranariea strain B, Providencia burhodogranariea strain D, Providencia rettgeri, and Providencia alcalifaciens. Using this laboratory-friendly and natural host, D. melanogaster, I determined how these bacteria differ in their ability to cause host mortality, replicate within the fly and trigger the fly's immune response as measured by transcription of antimicrobial peptides. Although each bacterium has a unique profile of these phenotypes, in general the greater amount of mortality a given bacterium causes, the more proliferative it is and the greater antimicrobial peptide transcription they evoke in the host. An exception to this was P. sneebia which killed about 90% of infected flies and reached greater numbers within the fly than any of the other bacteria, but induced less antimicrobial peptide transcription than the less virulent Providencia. Coinfections in D. melanogaster with P. sneebia and P. rettgeri, which induces greater antimicrobial peptide expression and is less virulent than P. sneebia, allowed me to conclude that P. sneebia is actively avoiding recognition by the immune response. I sequenced and annotated draft genomes of these four species then compared them to each other. I found that about 50% of each genome belongs to the Providencia core genome and about 15% of each genome consists of genes unique to that species. Four Providencia genomes of isolates originating from the human gut have also been sequenced, which include additional isolates of P. rettgeri and P. alcalifaciens as well as isolates of the species Providencia stuartii and Providencia rustigianii. When I compared orthologs of all eight sequenced Providencia genomes, I found that the percent of each genome that consists of the core genome and the unique genes stays largely the same. I found that each bacterium has type 3 secretion system, a known virulence factor. This means that presence of a type 3 secretion system does not correlate to those found to be virulent toward D. melanogaster. This work establishes D. melanogaster-Providencia as a model system for the study of host-pathogen interactions.