Staphylococcus pseudintermedius biofilms secrete factors that induce inflammatory reactions in vitro.

Biofilms, composed of bacterial cells embedded in a secreted polysaccharide and protein matrix, often cause problems such as chronic and refractory infections. Staphylococcus pseudintermedius, which is an important pathogen in veterinary medicine, has a high rate of biofilm production. Although it is considered that S. pseudintermedius biofilms are associated with prolonged inflammatory disorders, there are no reports that S. pseudintermedius biofilm directly regulates inflammatory reactions. In this study, we focused on the metabolites derived from biofilm cultures of S. pseudintermedius and evaluated their inflammatory effects in vitro. Expression levels of interleukin-1 beta and interleukin-6 mRNA significantly increased in RAW264.7 cells that were cultured with biofilm-conditioned medium (BCM). The secreted proteins in BCM were heat resistance and activated a Toll-like receptor (TLR) signalling pathway. Moreover, based on SDS-PAGE analysis, isolates with stronger biofilm-forming capabilities induced more inflammatory reactions and had specific banding patterns compared with those of weak biofilm producers. Collectively, our results suggest that the proteins derived from S. pseudintermedius biofilm induce a host inflammatory response via a TLR pathway. Furthermore, the severity of inflammation depends on the biofilm formation capacity of the S. pseudintermedius strain. SIGNIFICANCE AND IMPACT OF THE STUDY: Staphylococcus pseudintermedius is a biofilm-forming bacterium. We identified some biofilm secreted heat-resistant proteins that induce inflammatory reactions through Toll-like receptor signalling. The expression of the secreted protein varied depending on the potency of biofilm production. Our data suggest that these proteins may be the factors causing biofilm-related inflammation during S. pseudintermedius infections. Identification of these proteins may lead to the development of novel medications to prevent the exacerbation of infections caused by S. pseudintermedius.