Larvae As an Infection Model to Investigate SRNA-Mediated Pathogenesis in

Small regulatory RNAs (sRNAs) are key players in bacterial regulatory networks. Monitoring their expression inside living colonized or infected organisms is essential for identifying sRNA functions, but few studies have looked at sRNA expression during host infection with bacterial pathogens. Insufficient studies monitoring sRNA expression attest to the difficulties in collecting such data, we therefore developed a non-mammalian infection model using larval to analyze the roles of sRNAs during larval infection and to quickly determine possible sRNA involvement in staphylococcal virulence before proceeding to more complicated animal testing. We began by using the model to test infected larvae for immunohistochemical evidence of infection as well as host inflammatory responses over time. To monitor sRNA expression during infection, total RNAs were extracted from the larvae and invading bacteria at different time points. The expression profiles of the tested sRNAs were distinct and they fluctuated over time, with expression of both and increased during infection and associated with mortality, while expression remained barely detectable over time. A strong correlation was observed between expression and the mortality. To confirm these results, we used sRNA-knockout mutants to investigate sRNA involvement in   pathogenesis, finding that the decrease in death rates is delayed when either or was lacking. These results demonstrate the relevance of this model for investigating the role of sRNAs as transcriptional regulators involved in staphylococcal virulence. This insect model provides a fast and easy method for monitoring sRNA (and mRNA) participation in pathogenesis, and can also be used for other human bacterial pathogens.