Interspecies Biofilm Dynamics Among Staphylococci: Inflammatory Contributions to Chronic Rhinosinusitis

Staphylococcus species are frequently isolated from the sinonasal niche of chronic rhinosinusitis (CRS) patients. While Staphylococcus aureus is often associated with recalcitrant CRS, Staphylococcus epidermidis and Staphylococcus lugdunensis are largely deemed commensal. The purpose of this study was to investigate interspecies interactions and how those might influence inflammation and susceptibility to antibiotics.

Twelve staphylococcal isolates were harvested from six CRS patients, each infected with S. aureus and S. epidermidis, or with S. aureus and S. lugdunensis. Bacteria were cultured to allow biofilm formation in direct and indirect interspecies interactions, followed by measuring their biofilm biomass, antibiotic sensitivity, and toxicity and inflammatory potential when applied to human nasal epithelial cells (HNECs).

S. epidermidis produced up to 7.4-fold higher biomass than S. aureus in monocultures, with a reduction in S. epidermidis biomass under indirect coculture conditions with S. aureus biofilm (p < 0.05). In contrast, the biofilm biomass values of both S. lugdunensis and S. aureus were higher under indirect coculture conditions compared to monocultures for 2/3 paired isolates (p < 0.05). S. epidermidis monocultures and S. aureus/S. epidermidis cocultures were less toxic to HNECs than S. aureus monocultures. S. aureus and S. lugdunensis monocultures and S. aureus/S. lugdunensis cocultures induced interleukin-6 (IL-6) and toxicity to a similar extent versus controls. An increased tolerance to amoxicillin was observed for 2/3 S. epidermidis biofilm and for 3/3 S. lugdunensis biofilm when in indirect contact with S. aureus biofilm (p < 0.05).

Overall, staphylococcal interactions were highly strain specific, with S. aureus influencing the biofilm-forming capacity and increasing the tolerance to amoxicillin of both S. epidermidis and S. lugdunensis. S. epidermidis but not S. lugdunensis could mitigate S. aureus induced epithelial cytotoxicity. These findings support the complex nature of interactions among staphylococci with S. aureus and potentially S. lugdunensis having a pathogenic role and S. epidermidis a protective role within polymicrobial biofilms. Our findings have implications for the inflammatory potential and response to therapy of mixed biofilms.