Natural mutations in a Staphylococcus aureus virulence regulator attenuate cytotoxicity but permit bacteremia and abscess formation.
Das, S., Lindemann, C., Young, B. C., Muller, J., Österreich, B., Ternette, N., Winkler, A.-C., Paprotka, K., Reinhardt, R., Förstner, K. U., Allen, E., Flaxman, A., Yamaguchi, Y., Rollier, C. S., Van Diemen, P., Blättner, S., Remmele, C. W., Selle, M., Dittrich, M., Müller, T., Vogel, J., Ohlsen, K., Crook, D., Massey, R., Wilson, D. J., Rudel, T., Wyllie, D. H., and M. J. Fraunholz (2016)
Proceedings of the National Academy of Sciences USA 113: E3101-E3110. (pdf)
Staphylococcus aureus is a major bacterial pathogen, which causes severe blood and tissue infections that frequently emerge by autoinfection with asymptomatically carried nose and skin populations. However, recent studies report that bloodstream isolates differ systematically from those found in the nose and skin, exhibiting reduced toxicity towards leukocytes. In two patients, an attenuated toxicity bloodstream infection evolved from an asymptomatically carried high-toxicity nasal strain by loss-of-function mutations in the rsp transcription factor. Here, we report that rsp knockout mutants lead to global transcriptional and proteomic reprofiling, and exhibit the greatest signal in a genome-wide screen for genes influencing S. aureus survival in human cells. This effect is likely to be mediated in part via SSR42, a long non-coding RNA. We show that rsp controls SSR42 expression, is induced by hydrogen peroxide, and is required for normal cytotoxicity and hemolytic activity. Rsp inactivation in laboratory- and bacteremia-derived mutants attenuates toxin production, but upregulates other immune subversion proteins and reduces lethality during experimental infection. Crucially, inactivation of rsp preserves bacterial dissemination, as it affects neither formation of deep abscesses in mice, nor survival in human blood. Thus, we have identified a spontaneously evolving attenuated-cytotoxicity, non-hemolytic S. aureus phenotype, controlled by a pleiotropic transcriptional regulator/non-coding RNA virulence regulatory system, capable of causing S. aureus bloodstream infections. Such a phenotype could promote deep infection with limited early clinical manifestations, raising concerns that bacterial evolution within the human body may contribute to severe infection.