Our group is interested in virulence factors involved in this evasive strategy of S. aureus and their regulation. By means of a fluorescence microscopy, we determine the number of bacteria that are internalized by host cells, or how many of the internalized bacteria escape from their phagosome. Within the cytoplasm the bacteria divide and host cell death commences shortly thereafter. We screen for bacteria that are rendered unable to kill their respective host cells after internalization. We also employ whole libraries of transposon mutants, which can be screened in bulk by making use of massively parallel sequencing in a procedure termed TnSeq. Thereby, in a single experiment our group can assess many virulence genes simultaneously that are important in the investigated infection setting.
Using these techniques, we previously identified the involvement of a virulence regulator, Rsp, in S. aureus pathogenicity and dissemination (https://doi.org/10.1073/pnas.1520255113 ). Interestingly, the Rsp regulon involves various virulence factors, and drives transcription of a long non-coding RNA (lncRNA) SSR42 (https://doi.org/10.1128/jb.00252-18 ).
Another regulator, a LysR-Type transcription factor was found to be crucial for establishing infections at secondary infections sites such as bones or kidneys during bloodstream infection. This suggested that the regulator is required for adaptation to the infections sites during dissemination through the host (https://doi.org/10.1128/mBio.01646-20 ).
Further, we identified amphiphilic peptides (https://doi.org/10.1111/cmi.12233 ) as well as a non-ribosomal peptide synthetase (https://doi.org/10.1371/journal.ppat.1005857 ) as phagosomal escape factors. Host cell death involves calcium overload within the host cells (https://doi.org/10.1128/mBio.02250-2 ) as well as activity of a bacterial cysteine protease, staphopain (https://doi.org/10.1101/2020.02.10.936575 ). Thus, our group is interested in all aspects of S. aureus that reside within host cells.
Our current focus is the interaction of the bacteria with sphingolipids such as sphingomyelin and ceramide (https://doi.org/10.1101/2021.03.29.437456 ). We investigate the contribution of host and pathogen sphingomyelinases to S. aureus virulence.