Effect of sphingosine and inoculum concentrations on Staphylococcus aureus and Staphylococcus epidermidis biofilms

Atopic dermatitis (AD) is a chronic inflammatory skin disease where patients are more susceptible to infection and inflammation. The most salient symptoms of atopic dermatitis (AD) are skin dysbiosis and ceramide deficiency. Here, the effect of AD conditions on S. aureus resilience was investigated. S. aureus and S. epidermidis biofilms were co-inoculated at healthy and AD bacterial ratios and exposed to various sphingosine dosing regimens. In both healthy (S. epidermidis dominant) and AD (S. aureus dominant) conditions the viability of the non-dominant bacterial species was affected. Quorum sensing (QS)-impaired S. aureus was overall more susceptible to sphingosine. Despite the general resilience of QS-intact S. aureus against sphingosine, modulation of S. epidermidis (healthy ratio) and sphingosine (healthy Sph) led to a lack of recovery from its initial killing. Overall, it was found that when in biofilms, S. epidermidis increases S. aureus resilience to sphingosine, possibly enhancing the pathogen's recalcitrance in AD skin.