Staphylococcus aureus modulates the cell cycle of eukaryotic cells

Staphylococcus aureus is a Gram-positive bacterium responsible for a wide range of infections in humans and animals. Epithelial cells are able to sense microbes, creating an early line of defense against pathogens. Host cell cycle alteration is one of the highly sophisticated mechanisms pathogens use to hijack the main (defense) functions of the host cells, thus promoting their invasion and colonization. We investigated S. aureus-host epithelial cells interaction using multidisciplinary approaches. Bacteria slowed down cell proliferation and induced a cytopathic effect. We observed an enlargement of host cells at MOI 20:1, which started being visible from 72h post-infection. Increasing MOI to 100:1 resulted in the induction of apoptosis. Using flow cytometry analysis, we demonstrated that S. aureus induces a G2/M phase delay in synchronized HeLa cells, which was associated with accumulation of the cyclin-dependent kinase Cdk1/cdc2, a key inducer of mitosis entry, and with the accumulation of unphosphorylated histone H3, which was correlated with a dramatic reduction of the mitotic cell number. This delay required the presence of live S. aureus since the addition of the heat-killed bacteria did not alter the cell cycle. Analysis of S. aureus proliferation in asynchronous, G1- and G2-phase-enriched HeLa cells showed that the G2 phase was preferential for bacterial infective efficiency, suggesting that the G2 phase delay may be used by S. aureus for propagation within the host. To shed light on the nature of the active substance(s), S. aureus cells and culture supernatants were tested for their capacity to modify HeLa cell cycle. Concentrated S. aureus culture supernatants exerted an effect comparable to that of bacteria, suggesting that the molecule(s) that are involved in the alteration of the cell cycle are secreted by S. aureus strains into the environment. To understand whether this phenomenon is a common feature of all S. aureus strains, four S. aureus strains obtained from patients with diagnosed staphylococcal enterocolitis were investigated on their capacity to alter host’s cell cycle. Using flow cytometry, we demonstrated that the supernatant of one out of the four S. aureus strains analyzed clearly induced a delayed G2/M phase transition of HeLa cells, suggesting a strain-dependency of this phenotype. To characterize the active molecule, MW2 S. aureus supernatant as well as DMEM medium were fractionated using size-exclusion chromatography. The activity of each fraction was evaluated on synchronous HeLa cells. Subsequent characterization of active fractions was performed by mass spectrometry. A number of molecules were detected in the active fractions when compared to the negative control. Our results show the potential of S. aureus to subvert key cellular processes such as cell cycle progression, and open the new perspectives for the investigation of the mechanisms of the S. aureus infection