Comparative pathology of bacteria in the genus Providencia to a natural host, Drosophila melanogaster.

Bacteria in the genus Providencia are pathogens of many organisms, including humans and insects. We and colleagues have isolated five different strains belonging to four distinct Providencia species as natural infections of Drosophila melanogaster captured in the wild. We found that these isolates vary considerably in pathology to infected D. melanogaster, differing in the level of mortality they cause, their ability to replicate within the host and the level that the fly's immune response is elicited. One interesting bacterium was Providencia sneebia, which causes nearly complete mortality and reaches large numbers in the fly but does not elicit a comparably strong immune response. Through coinfection experiments, we determined that P. sneebia avoids recognition by the immune system. We tested for biofilm formation and replication within D. melanogaster cells as possible mechanisms for P. sneebia escape from host immunity, but did not find evidence for either. D. melanogaster and Providencia provide a powerful system for studying general host-pathogen interactions, and for understanding how the well-studied immune model host D. melanogaster interacts with its natural bacterial pathogens.