Pneumococcal infections have increasingly high mortality rates despite the availability of vaccines and antibiotics.Therefore, the identification of new virulence determinants and the T-shirt understanding of the molecular mechanisms behind pathogenesis have become of paramount importance in the search of new targets for drug development.The exoribonuclease RNase R has been involved in virulence in a growing number of pathogens.In this work, we used Galleria mellonella as an infection model to demonstrate that the presence of RNase R increases the pneumococcus virulence.
Larvae infected with the RNase R mutant show an increased expression level of antimicrobial peptides.Furthermore, they have a lower bacterial load in the hemolymph in the later stages of infection, leading to a higher survival rate of the larvae.Interestingly, pneumococci expressing RNase R show a sudden drop in bacterial numbers immediately after infection, resembling the eclipse phase observed after intravenous inoculation in mice.Concomitantly, we observed a lower number of mutant bacteria inside larval hemocytes and a higher susceptibility to oxidative stress when compared to the wild type.
Together, our results indicate that RNase R is involved in the ability of pneumococci to evade the host immune response, probably by switch assembly interfering with internalization and/or replication inside the larval hemocytes.