Staphylococcus aureus adaptive response to antibiotic stress under physiological conditions: Effects on persistence and phenotype

Staphylococcus aureus is an important human pathobiont, colonising about a third of the population and potentially causing difficult-to-treat infections due to antimicrobial resistance and persistence. Persistence is a bacterial response to a stressor, allowing a small subpopulation of bacteria to transiently survive otherwise lethal antibiotic concentrations despite being fully susceptible. The capability of S. aureus to persist within its human host is closely connected with its ability to interact with a changing environment and to rapidly adapt. To further elucidate the time window required to trigger such persistence under a precise time exposure in S. aureus, we sequentially exposed S. aureus to different classes of antibiotics as well as primary immune cells. In this study, we showed that pre-exposure to antibiotics at 40x minimum inhibitory concentration during a time window of 4h is sufficient for a reduction in viable bacterial cells and a change in colony size. Furthermore, we exposed those surviving bacteria to a secondary stressor: either another set of antibiotics or primary immune cells. For the sequential exposure to different classes of antibiotics, we showed high dependencies of survival and phenotypic heterogeneity on treatment combination and strain. We observed that preexposure to antibiotics for a period of 4h prior to infection of human monocyte-derived cells increased intracellular survival after 14h and led to a change in phenotypic heterogeneity. We show that S. aureus adapts to environmental challenges such as exposure to antibiotics or innate immune cells, evidencing the influence of sequential treatment combinations and strain-specific response on the development of persistence