Plague bacteria (Yersinia pestis) are transmitted to susceptible mammals by fleas. At least 25 flea species found in North America have been identified as plague vectors. The most efficient flea vector is the Oriental rat flea Xenopsylla cheopis, while the cat flea Ctenocephalides felis is a poor vector. The factors that determine vector competence of different fleas are not known. The main obstacles that the bacteria must overcome in the flea gut are also unknown. Fleas' molecular responses to Y. pestis invading could be a determining factor to control the bacterial survival and growth. Good and poor vectors might have different gene expression patterns when they are infected with Y. pestis. To investigate this hypothesis, we constructed cDNA libraries of infected fleas (X. cheopis and C. felis) using Suppression Subtractive Hybridization at 1 and 2 days post-infection. The infection approaches were either hemocoel injection or oral infection. We measured expression of several of the genes using quantitative real-time PCR. The results indicated that changes in gene expression were modest. We observed that the route of infection (oral vs. hemocoel injection) had a strong effect on the genes that were upregulated, with hemocoel injection inducing more obvious immune-related genes than oral infection. We also saw that infected X. cheopis has different gene expression patterns than infected C. felis. Several of the genes from both species are predicted to be involved in production and removal of reactive oxygen species (ROS). Consistent with this observation, the levels of peroxide in X. cheopis midguts was higher following oral infection with Y. pestis, than in uninfected fleas, and Y. pestis grew differently in antioxidant-fed fleas, demonstrating that ROS production could be an important defense in fleas early after infection



College and Department

Life Sciences; Microbiology and Molecular Biology



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Yersinia pestis, fleas, vectors, gene expression, ROS



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Microbiology Commons