Biological vector borne transmission of Salmonella by cockroaches - PROJECT SUMMARY The German cockroach, Blattella germanica, is the most common pestiferous cockroach species in human environments. B. germanica contributes to the transmission of bacteria that cause enteric (diarrheal) disease, including Salmonella enterica serovar Typhimurium, but the mechanisms of transmission are not well understood. Enteric bacterial pathogen transmission by cockroaches has previously been described as mechanical in nature. Mechanical transmission is a passive, non-replicative transfer of bacteria from one location or host to another. This mechanism is limited in impact relative to active biological transmission. However, recent data from our laboratory indicate that transmission of S. Typhimurium by German cockroaches is markedly more complex than simple mechanical transmission and instead resembles biological transmission by other insects that intake bacteria from infected hosts and are subsequently colonized, enabling active and prolonged shedding and transmission. In particular, we have observed that following ingestion, S. Typhimurium undergoes a lifestyle change and multiple replication events in the digestive tract of the German cockroach. Furthermore, we have identified several S. Typhimurium genes that are necessary for bacterial colonization and shedding from the gut of B. germanica, evidencing an active role of the bacteria. The central objective of the proposed research project is to gain a detailed understanding of the mechanisms of biological vector-borne transmission of S. Typhimurium by the German cockroach. Three independent specific aims are proposed. First, we will elucidate the fine spatiotemporal details of wild-type S. Typhimurium colonization and shedding in nymph and adult cockroaches. Second, leveraging an unparalleled array of mutant S. Typhimurium strains, we will identify specific bacterial genes and functions that are necessary for colonization of cockroaches and subsequent transmission. Third, we will determine the effects of two key host factors, namely antimicrobial effectors and the gut microbiota, on S. Typhimurium colonization and shedding. Together, the proposed studies will establish a picture of how bacterial and host factors interact to shape biological transmission of S. Typhimurium by the German cockroach, providing fundamental insight into the dynamics of a unique, poorly studied vector-pathogen system with a global distribution and public health impact.
